[PATCH 00/21] kthread: Introduce preferred affinity v5

[PATCH 00/21] kthread: Introduce preferred affinity v5

[Frederic Weisbecker]

Affining kthreads follow either of 4 existing different patterns:

1) Per-CPU kthreads must stay affine to a single CPU and never execute
   relevant code on any other CPU. This is currently handled by smpboot
   code which takes care of CPU-hotplug operations.

2) Kthreads that _have_ to be affine to a specific set of CPUs and can't
   run anywhere else. The affinity is set through kthread_bind_mask()
   and the subsystem takes care by itself to handle CPU-hotplug operations.

3) Kthreads that _prefer_ to be affine to a specific NUMA node.

4) Similar to the previous point but kthreads have a _preferred_ affinity
   different than a node. It is set manually like any other task and
   CPU-hotplug is supposed to be handled by the relevant subsystem so
   that the task is properly reaffined whenever a given CPU from the
   preferred affinity comes up or down. Also care must be taken so that
   the preferred affinity doesn't cross housekeeping cpumask boundaries.

Currently the preferred affinity patterns (3 and 4) have at least 4
identified users, with more or less success when it comes to handle
CPU-hotplug operations and CPU isolation.

This is an infrastructure proposal to handle this (after cleanups from 01
to 10).

Changes since v4:

* Collect more tags
* Fix a title (Vishal Chourasia)
* Handle mismatched 32bits el0 support on arm64, see patches 11 and 12
  (Will Deacon)

Frederic Weisbecker (21):
  arm/bL_switcher: Use kthread_run_on_cpu()
  x86/resctrl: Use kthread_run_on_cpu()
  firmware: stratix10-svc: Use kthread_run_on_cpu()
  scsi: bnx2fc: Use kthread_create_on_cpu()
  scsi: bnx2i: Use kthread_create_on_cpu()
  scsi: qedi: Use kthread_create_on_cpu()
  soc/qman: test: Use kthread_run_on_cpu()
  kallsyms: Use kthread_run_on_cpu()
  lib: test_objpool: Use kthread_run_on_cpu()
  net: pktgen: Use kthread_create_on_cpu()
  arm64: Keep first mismatched 32bits el0 capable CPU online through its
    callbacks
  sched,arm64: Handle CPU isolation on last resort fallback rq selection
  kthread: Make sure kthread hasn't started while binding it
  kthread: Default affine kthread to its preferred NUMA node
  mm: Create/affine kcompactd to its preferred node
  mm: Create/affine kswapd to its preferred node
  kthread: Implement preferred affinity
  rcu: Use kthread preferred affinity for RCU boost
  kthread: Unify kthread_create_on_cpu() and
    kthread_create_worker_on_cpu() automatic format
  treewide: Introduce kthread_run_worker[_on_cpu]()
  rcu: Use kthread preferred affinity for RCU exp kworkers

 arch/arm/common/bL_switcher.c                 |  10 +-
 arch/arm64/include/asm/cpufeature.h           |   1 +
 arch/arm64/include/asm/mmu_context.h          |   2 +
 arch/arm64/kernel/cpufeature.c                |  75 +++++--
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c     |  28 +--
 arch/x86/kvm/i8254.c                          |   2 +-
 crypto/crypto_engine.c                        |   2 +-
 drivers/cpufreq/cppc_cpufreq.c                |   2 +-
 drivers/firmware/stratix10-svc.c              |   9 +-
 drivers/gpu/drm/drm_vblank_work.c             |   2 +-
 .../drm/i915/gem/selftests/i915_gem_context.c |   2 +-
 drivers/gpu/drm/i915/gt/selftest_execlists.c  |   2 +-
 drivers/gpu/drm/i915/gt/selftest_hangcheck.c  |   2 +-
 drivers/gpu/drm/i915/gt/selftest_slpc.c       |   2 +-
 drivers/gpu/drm/i915/selftests/i915_request.c |   8 +-
 drivers/gpu/drm/msm/disp/msm_disp_snapshot.c  |   2 +-
 drivers/gpu/drm/msm/msm_atomic.c              |   2 +-
 drivers/gpu/drm/msm/msm_gpu.c                 |   2 +-
 drivers/gpu/drm/msm/msm_kms.c                 |   2 +-
 .../platform/chips-media/wave5/wave5-vpu.c    |   2 +-
 drivers/net/dsa/mv88e6xxx/chip.c              |   2 +-
 drivers/net/ethernet/intel/ice/ice_dpll.c     |   2 +-
 drivers/net/ethernet/intel/ice/ice_gnss.c     |   2 +-
 drivers/net/ethernet/intel/ice/ice_ptp.c      |   2 +-
 drivers/platform/chrome/cros_ec_spi.c         |   2 +-
 drivers/ptp/ptp_clock.c                       |   2 +-
 drivers/scsi/bnx2fc/bnx2fc_fcoe.c             |   7 +-
 drivers/scsi/bnx2i/bnx2i_init.c               |   7 +-
 drivers/scsi/qedi/qedi_main.c                 |   6 +-
 drivers/soc/fsl/qbman/qman_test_stash.c       |   6 +-
 drivers/spi/spi.c                             |   2 +-
 drivers/usb/typec/tcpm/tcpm.c                 |   2 +-
 drivers/vdpa/vdpa_sim/vdpa_sim.c              |   2 +-
 drivers/watchdog/watchdog_dev.c               |   2 +-
 fs/erofs/zdata.c                              |   2 +-
 include/linux/cpuhotplug.h                    |   1 +
 include/linux/kthread.h                       |  56 ++++-
 include/linux/mmu_context.h                   |   1 +
 kernel/kallsyms_selftest.c                    |   4 +-
 kernel/kthread.c                              | 201 ++++++++++++++++--
 kernel/rcu/tree.c                             |  94 ++------
 kernel/rcu/tree_plugin.h                      |  11 +-
 kernel/sched/core.c                           |   2 +-
 kernel/sched/ext.c                            |   2 +-
 kernel/workqueue.c                            |   2 +-
 lib/test_objpool.c                            |  19 +-
 mm/compaction.c                               |  43 +---
 mm/vmscan.c                                   |   8 +-
 net/core/pktgen.c                             |   7 +-
 net/dsa/tag_ksz.c                             |   2 +-
 net/dsa/tag_ocelot_8021q.c                    |   2 +-
 net/dsa/tag_sja1105.c                         |   2 +-
 52 files changed, 384 insertions(+), 280 deletions(-)

-- 
2.46.0

[PATCH 01/21] arm/bL_switcher: Use kthread_run_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 arch/arm/common/bL_switcher.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/arm/common/bL_switcher.c b/arch/arm/common/bL_switcher.c
index 9a9aa53547a6..d1e82a318e3b 100644
--- a/arch/arm/common/bL_switcher.c
+++ b/arch/arm/common/bL_switcher.c
@@ -307,13 +307,11 @@ static struct task_struct *bL_switcher_thread_create(int cpu, void *arg)
 {
 	struct task_struct *task;
 
-	task = kthread_create_on_node(bL_switcher_thread, arg,
-				      cpu_to_node(cpu), "kswitcher_%d", cpu);
-	if (!IS_ERR(task)) {
-		kthread_bind(task, cpu);
-		wake_up_process(task);
-	} else
+	task = kthread_run_on_cpu(bL_switcher_thread, arg,
+				  cpu, "kswitcher_%d");
+	if (IS_ERR(task))
 		pr_err("%s failed for CPU %d\n", __func__, cpu);
+
 	return task;
 }
 
-- 
2.46.0

[PATCH 02/21] x86/resctrl: Use kthread_run_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

Acked-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 28 +++++++----------------
 1 file changed, 8 insertions(+), 20 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
index 972e6b6b0481..6c60c16a9dd0 100644
--- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
+++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
@@ -1205,20 +1205,14 @@ static int pseudo_lock_measure_cycles(struct rdtgroup *rdtgrp, int sel)
 	plr->cpu = cpu;
 
 	if (sel == 1)
-		thread = kthread_create_on_node(measure_cycles_lat_fn, plr,
-						cpu_to_node(cpu),
-						"pseudo_lock_measure/%u",
-						cpu);
+		thread = kthread_run_on_cpu(measure_cycles_lat_fn, plr,
+					    cpu, "pseudo_lock_measure/%u");
 	else if (sel == 2)
-		thread = kthread_create_on_node(measure_l2_residency, plr,
-						cpu_to_node(cpu),
-						"pseudo_lock_measure/%u",
-						cpu);
+		thread = kthread_run_on_cpu(measure_l2_residency, plr,
+					    cpu, "pseudo_lock_measure/%u");
 	else if (sel == 3)
-		thread = kthread_create_on_node(measure_l3_residency, plr,
-						cpu_to_node(cpu),
-						"pseudo_lock_measure/%u",
-						cpu);
+		thread = kthread_run_on_cpu(measure_l3_residency, plr,
+					    cpu, "pseudo_lock_measure/%u");
 	else
 		goto out;
 
@@ -1226,8 +1220,6 @@ static int pseudo_lock_measure_cycles(struct rdtgroup *rdtgrp, int sel)
 		ret = PTR_ERR(thread);
 		goto out;
 	}
-	kthread_bind(thread, cpu);
-	wake_up_process(thread);
 
 	ret = wait_event_interruptible(plr->lock_thread_wq,
 				       plr->thread_done == 1);
@@ -1315,18 +1307,14 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
 
 	plr->thread_done = 0;
 
-	thread = kthread_create_on_node(pseudo_lock_fn, rdtgrp,
-					cpu_to_node(plr->cpu),
-					"pseudo_lock/%u", plr->cpu);
+	thread = kthread_run_on_cpu(pseudo_lock_fn, rdtgrp,
+				    plr->cpu, "pseudo_lock/%u");
 	if (IS_ERR(thread)) {
 		ret = PTR_ERR(thread);
 		rdt_last_cmd_printf("Locking thread returned error %d\n", ret);
 		goto out_cstates;
 	}
 
-	kthread_bind(thread, plr->cpu);
-	wake_up_process(thread);
-
 	ret = wait_event_interruptible(plr->lock_thread_wq,
 				       plr->thread_done == 1);
 	if (ret < 0) {
-- 
2.46.0

[PATCH 03/21] firmware: stratix10-svc: Use kthread_run_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 drivers/firmware/stratix10-svc.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/firmware/stratix10-svc.c b/drivers/firmware/stratix10-svc.c
index 528f37417aea..4cf5bd5647a4 100644
--- a/drivers/firmware/stratix10-svc.c
+++ b/drivers/firmware/stratix10-svc.c
@@ -967,18 +967,15 @@ int stratix10_svc_send(struct stratix10_svc_chan *chan, void *msg)
 	/* first client will create kernel thread */
 	if (!chan->ctrl->task) {
 		chan->ctrl->task =
-			kthread_create_on_node(svc_normal_to_secure_thread,
-					      (void *)chan->ctrl,
-					      cpu_to_node(cpu),
-					      "svc_smc_hvc_thread");
+			kthread_run_on_cpu(svc_normal_to_secure_thread,
+					   (void *)chan->ctrl,
+					   cpu, "svc_smc_hvc_thread");
 			if (IS_ERR(chan->ctrl->task)) {
 				dev_err(chan->ctrl->dev,
 					"failed to create svc_smc_hvc_thread\n");
 				kfree(p_data);
 				return -EINVAL;
 			}
-		kthread_bind(chan->ctrl->task, cpu);
-		wake_up_process(chan->ctrl->task);
 	}
 
 	pr_debug("%s: sent P-va=%p, P-com=%x, P-size=%u\n", __func__,
-- 
2.46.0

[PATCH 04/21] scsi: bnx2fc: Use kthread_create_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

However it looks like bnx2fc_percpu_io_thread() kthread could be
replaced by the use of a high prio workqueue instead.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 drivers/scsi/bnx2fc/bnx2fc_fcoe.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/bnx2fc/bnx2fc_fcoe.c b/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
index f49783b89d04..36126030e76d 100644
--- a/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
+++ b/drivers/scsi/bnx2fc/bnx2fc_fcoe.c
@@ -2610,14 +2610,11 @@ static int bnx2fc_cpu_online(unsigned int cpu)
 
 	p = &per_cpu(bnx2fc_percpu, cpu);
 
-	thread = kthread_create_on_node(bnx2fc_percpu_io_thread,
-					(void *)p, cpu_to_node(cpu),
-					"bnx2fc_thread/%d", cpu);
+	thread = kthread_create_on_cpu(bnx2fc_percpu_io_thread,
+				       (void *)p, cpu, "bnx2fc_thread/%d");
 	if (IS_ERR(thread))
 		return PTR_ERR(thread);
 
-	/* bind thread to the cpu */
-	kthread_bind(thread, cpu);
 	p->iothread = thread;
 	wake_up_process(thread);
 	return 0;
-- 
2.46.0

[PATCH 05/21] scsi: bnx2i: Use kthread_create_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

However it looks like bnx2i_percpu_io_thread() kthread could be
replaced by the use of a high prio workqueue instead.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 drivers/scsi/bnx2i/bnx2i_init.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/bnx2i/bnx2i_init.c b/drivers/scsi/bnx2i/bnx2i_init.c
index 872ad37e2a6e..cecc3a026762 100644
--- a/drivers/scsi/bnx2i/bnx2i_init.c
+++ b/drivers/scsi/bnx2i/bnx2i_init.c
@@ -415,14 +415,11 @@ static int bnx2i_cpu_online(unsigned int cpu)
 
 	p = &per_cpu(bnx2i_percpu, cpu);
 
-	thread = kthread_create_on_node(bnx2i_percpu_io_thread, (void *)p,
-					cpu_to_node(cpu),
-					"bnx2i_thread/%d", cpu);
+	thread = kthread_create_on_cpu(bnx2i_percpu_io_thread, (void *)p,
+				       cpu, "bnx2i_thread/%d");
 	if (IS_ERR(thread))
 		return PTR_ERR(thread);
 
-	/* bind thread to the cpu */
-	kthread_bind(thread, cpu);
 	p->iothread = thread;
 	wake_up_process(thread);
 	return 0;
-- 
2.46.0

[PATCH 06/21] scsi: qedi: Use kthread_create_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

However it looks like qedi_percpu_io_thread() kthread could be
replaced by the use of a high prio workqueue instead.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 drivers/scsi/qedi/qedi_main.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/scsi/qedi/qedi_main.c b/drivers/scsi/qedi/qedi_main.c
index c5aec26019d6..4b2a9cd811c4 100644
--- a/drivers/scsi/qedi/qedi_main.c
+++ b/drivers/scsi/qedi/qedi_main.c
@@ -1960,13 +1960,11 @@ static int qedi_cpu_online(unsigned int cpu)
 	struct qedi_percpu_s *p = this_cpu_ptr(&qedi_percpu);
 	struct task_struct *thread;
 
-	thread = kthread_create_on_node(qedi_percpu_io_thread, (void *)p,
-					cpu_to_node(cpu),
-					"qedi_thread/%d", cpu);
+	thread = kthread_create_on_cpu(qedi_percpu_io_thread, (void *)p,
+				       cpu, "qedi_thread/%d");
 	if (IS_ERR(thread))
 		return PTR_ERR(thread);
 
-	kthread_bind(thread, cpu);
 	p->iothread = thread;
 	wake_up_process(thread);
 	return 0;
-- 
2.46.0

[PATCH 07/21] soc/qman: test: Use kthread_run_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

However it looks like kthreads here could be replaced by the use of a
per-cpu workqueue instead.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 drivers/soc/fsl/qbman/qman_test_stash.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/soc/fsl/qbman/qman_test_stash.c b/drivers/soc/fsl/qbman/qman_test_stash.c
index b7e8e5ec884c..f4d3c2146f4f 100644
--- a/drivers/soc/fsl/qbman/qman_test_stash.c
+++ b/drivers/soc/fsl/qbman/qman_test_stash.c
@@ -108,14 +108,12 @@ static int on_all_cpus(int (*fn)(void))
 			.fn = fn,
 			.started = ATOMIC_INIT(0)
 		};
-		struct task_struct *k = kthread_create(bstrap_fn, &bstrap,
-			"hotpotato%d", cpu);
+		struct task_struct *k = kthread_run_on_cpu(bstrap_fn, &bstrap,
+							   cpu, "hotpotato%d");
 		int ret;
 
 		if (IS_ERR(k))
 			return -ENOMEM;
-		kthread_bind(k, cpu);
-		wake_up_process(k);
 		/*
 		 * If we call kthread_stop() before the "wake up" has had an
 		 * effect, then the thread may exit with -EINTR without ever
-- 
2.46.0

[PATCH 08/21] kallsyms: Use kthread_run_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/kallsyms_selftest.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/kallsyms_selftest.c b/kernel/kallsyms_selftest.c
index 873f7c445488..cf4af5728307 100644
--- a/kernel/kallsyms_selftest.c
+++ b/kernel/kallsyms_selftest.c
@@ -435,13 +435,11 @@ static int __init kallsyms_test_init(void)
 {
 	struct task_struct *t;
 
-	t = kthread_create(test_entry, NULL, "kallsyms_test");
+	t = kthread_run_on_cpu(test_entry, NULL, 0, "kallsyms_test");
 	if (IS_ERR(t)) {
 		pr_info("Create kallsyms selftest task failed\n");
 		return PTR_ERR(t);
 	}
-	kthread_bind(t, 0);
-	wake_up_process(t);
 
 	return 0;
 }
-- 
2.46.0

[PATCH 09/21] lib: test_objpool: Use kthread_run_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

Reviewed-by: Matt Wu <wuqiang.matt@bytedance.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 lib/test_objpool.c | 19 +++++--------------
 1 file changed, 5 insertions(+), 14 deletions(-)

diff --git a/lib/test_objpool.c b/lib/test_objpool.c
index 5a3f6961a70f..896c0131c9a8 100644
--- a/lib/test_objpool.c
+++ b/lib/test_objpool.c
@@ -371,14 +371,10 @@ static int ot_start_sync(struct ot_test *test)
 		if (!cpu_online(cpu))
 			continue;
 
-		work = kthread_create_on_node(ot_thread_worker, item,
-				cpu_to_node(cpu), "ot_worker_%d", cpu);
-		if (IS_ERR(work)) {
+		work = kthread_run_on_cpu(ot_thread_worker, item,
+					  cpu, "ot_worker_%d");
+		if (IS_ERR(work))
 			pr_err("failed to create thread for cpu %d\n", cpu);
-		} else {
-			kthread_bind(work, cpu);
-			wake_up_process(work);
-		}
 	}
 
 	/* wait a while to make sure all threads waiting at start line */
@@ -562,14 +558,9 @@ static int ot_start_async(struct ot_test *test)
 		if (!cpu_online(cpu))
 			continue;
 
-		work = kthread_create_on_node(ot_thread_worker, item,
-				cpu_to_node(cpu), "ot_worker_%d", cpu);
-		if (IS_ERR(work)) {
+		work = kthread_run_on_cpu(ot_thread_worker, item, cpu, "ot_worker_%d");
+		if (IS_ERR(work))
 			pr_err("failed to create thread for cpu %d\n", cpu);
-		} else {
-			kthread_bind(work, cpu);
-			wake_up_process(work);
-		}
 	}
 
 	/* wait a while to make sure all threads waiting at start line */
-- 
2.46.0

[PATCH 10/21] net: pktgen: Use kthread_create_on_cpu()

[Frederic Weisbecker]

Use the proper API instead of open coding it.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
---
 net/core/pktgen.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 34f68ef74b8f..7fcb4fc7a5d6 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -3883,17 +3883,14 @@ static int __net_init pktgen_create_thread(int cpu, struct pktgen_net *pn)
 	list_add_tail(&t->th_list, &pn->pktgen_threads);
 	init_completion(&t->start_done);
 
-	p = kthread_create_on_node(pktgen_thread_worker,
-				   t,
-				   cpu_to_node(cpu),
-				   "kpktgend_%d", cpu);
+	p = kthread_create_on_cpu(pktgen_thread_worker, t, cpu, "kpktgend_%d");
 	if (IS_ERR(p)) {
 		pr_err("kthread_create_on_node() failed for cpu %d\n", t->cpu);
 		list_del(&t->th_list);
 		kfree(t);
 		return PTR_ERR(p);
 	}
-	kthread_bind(p, cpu);
+
 	t->tsk = p;
 
 	pe = proc_create_data(t->tsk->comm, 0600, pn->proc_dir,
-- 
2.46.0

[PATCH 11/21] arm64: Keep first mismatched 32bits el0 capable CPU online through its callbacks

[Frederic Weisbecker]

The first mismatched 32bits el0 capable CPU is designated as the last
resort CPU for compat 32 bits tasks. As such this CPU is forbidden to
go offline.

However this restriction is applied to the device object of the CPU,
which is not easy to revert later if needed because other components may
have forbidden the target to be offline and they are not tracked.

But the task cpu possible mask is going to be made aware of housekeeping
CPUs. In that context, a better 32 bits el0 last resort CPU may be found
later on boot. When that happens, the old fallback can be made
offlineable again.

To make this possible and more flexible, drive the offlineable decision
from the cpuhotplug callbacks themselves.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 arch/arm64/kernel/cpufeature.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 718728a85430..53ee8ce38d5b 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -3591,15 +3591,15 @@ void __init setup_user_features(void)
 	minsigstksz_setup();
 }
 
-static int enable_mismatched_32bit_el0(unsigned int cpu)
-{
-	/*
-	 * The first 32-bit-capable CPU we detected and so can no longer
-	 * be offlined by userspace. -1 indicates we haven't yet onlined
-	 * a 32-bit-capable CPU.
-	 */
-	static int lucky_winner = -1;
+/*
+ * The first 32-bit-capable CPU we detected and so can no longer
+ * be offlined by userspace. -1 indicates we haven't yet onlined
+ * a 32-bit-capable CPU.
+ */
+static int cpu_32bit_unofflineable = -1;
 
+static int mismatched_32bit_el0_online(unsigned int cpu)
+{
 	struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu);
 	bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0);
 
@@ -3611,7 +3611,7 @@ static int enable_mismatched_32bit_el0(unsigned int cpu)
 	if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit)
 		return 0;
 
-	if (lucky_winner >= 0)
+	if (cpu_32bit_unofflineable < 0)
 		return 0;
 
 	/*
@@ -3619,16 +3619,20 @@ static int enable_mismatched_32bit_el0(unsigned int cpu)
 	 * 32-bit EL0 online so that is_cpu_allowed() doesn't end up rejecting
 	 * every CPU in the system for a 32-bit task.
 	 */
-	lucky_winner = cpu_32bit ? cpu : cpumask_any_and(cpu_32bit_el0_mask,
-							 cpu_active_mask);
-	get_cpu_device(lucky_winner)->offline_disabled = true;
+	cpu_32bit_unofflineable = cpu_32bit ? cpu : cpumask_any_and(cpu_32bit_el0_mask,
+								    cpu_active_mask);
 	setup_elf_hwcaps(compat_elf_hwcaps);
 	elf_hwcap_fixup();
 	pr_info("Asymmetric 32-bit EL0 support detected on CPU %u; CPU hot-unplug disabled on CPU %u\n",
-		cpu, lucky_winner);
+		cpu, cpu_32bit_unofflineable);
 	return 0;
 }
 
+static int mismatched_32bit_el0_offline(unsigned int cpu)
+{
+	return cpu == cpu_32bit_unofflineable ? -EBUSY : 0;
+}
+
 static int __init init_32bit_el0_mask(void)
 {
 	if (!allow_mismatched_32bit_el0)
@@ -3639,7 +3643,7 @@ static int __init init_32bit_el0_mask(void)
 
 	return cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 				 "arm64/mismatched_32bit_el0:online",
-				 enable_mismatched_32bit_el0, NULL);
+				 mismatched_32bit_el0_online, mismatched_32bit_el0_offline);
 }
 subsys_initcall_sync(init_32bit_el0_mask);
 
-- 
2.46.0

[PATCH 12/21] sched,arm64: Handle CPU isolation on last resort fallback rq selection

[Frederic Weisbecker]

When a kthread or any other task has an affinity mask that is fully
offline or unallowed, the scheduler reaffines the task to all possible
CPUs as a last resort.

This default decision doesn't mix up very well with nohz_full CPUs that
are part of the possible cpumask but don't want to be disturbed by
unbound kthreads or even detached pinned user tasks.

Make the fallback affinity setting aware of nohz_full. ARM64 is a
special case and its last resort EL0 32bits capable CPU can be updated
as housekeeping CPUs appear on boot.

Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 arch/arm64/include/asm/cpufeature.h  |  1 +
 arch/arm64/include/asm/mmu_context.h |  2 ++
 arch/arm64/kernel/cpufeature.c       | 49 +++++++++++++++++++++++-----
 include/linux/mmu_context.h          |  1 +
 kernel/sched/core.c                  |  2 +-
 5 files changed, 46 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 3d261cc123c1..992d782f2899 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -663,6 +663,7 @@ static inline bool supports_clearbhb(int scope)
 }
 
 const struct cpumask *system_32bit_el0_cpumask(void);
+const struct cpumask *fallback_32bit_el0_cpumask(void);
 DECLARE_STATIC_KEY_FALSE(arm64_mismatched_32bit_el0);
 
 static inline bool system_supports_32bit_el0(void)
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index 7c09d47e09cb..8d481e16271b 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -282,6 +282,8 @@ task_cpu_possible_mask(struct task_struct *p)
 }
 #define task_cpu_possible_mask	task_cpu_possible_mask
 
+const struct cpumask *task_cpu_fallback_mask(struct task_struct *p);
+
 void verify_cpu_asid_bits(void);
 void post_ttbr_update_workaround(void);
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 53ee8ce38d5b..4eabe0f02cc8 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -75,6 +75,7 @@
 #include <linux/cpu.h>
 #include <linux/kasan.h>
 #include <linux/percpu.h>
+#include <linux/sched/isolation.h>
 
 #include <asm/cpu.h>
 #include <asm/cpufeature.h>
@@ -133,6 +134,7 @@ DEFINE_STATIC_KEY_FALSE(arm64_mismatched_32bit_el0);
  * Only valid if arm64_mismatched_32bit_el0 is enabled.
  */
 static cpumask_var_t cpu_32bit_el0_mask __cpumask_var_read_mostly;
+static cpumask_var_t fallback_32bit_el0_mask __cpumask_var_read_mostly;
 
 void dump_cpu_features(void)
 {
@@ -1618,6 +1620,23 @@ const struct cpumask *system_32bit_el0_cpumask(void)
 	return cpu_possible_mask;
 }
 
+const struct cpumask *task_cpu_fallback_mask(struct task_struct *p)
+{
+	if (!static_branch_unlikely(&arm64_mismatched_32bit_el0))
+		return housekeeping_cpumask(HK_TYPE_TICK);
+
+	if (!is_compat_thread(task_thread_info(p)))
+		return housekeeping_cpumask(HK_TYPE_TICK);
+
+	if (!system_supports_32bit_el0())
+		return cpu_none_mask;
+
+	if (!cpumask_empty(fallback_32bit_el0_mask))
+		return fallback_32bit_el0_mask;
+	else
+		return cpu_32bit_el0_mask;
+}
+
 static int __init parse_32bit_el0_param(char *str)
 {
 	allow_mismatched_32bit_el0 = true;
@@ -3605,22 +3624,33 @@ static int mismatched_32bit_el0_online(unsigned int cpu)
 
 	if (cpu_32bit) {
 		cpumask_set_cpu(cpu, cpu_32bit_el0_mask);
+		if (housekeeping_cpu(cpu, HK_TYPE_TICK))
+			cpumask_set_cpu(cpu, fallback_32bit_el0_mask);
 		static_branch_enable_cpuslocked(&arm64_mismatched_32bit_el0);
 	}
 
+	if (cpu_32bit_unofflineable >= 0) {
+		if (!housekeeping_cpu(cpu_32bit_unofflineable, HK_TYPE_TICK) &&
+		    cpu_32bit && housekeeping_cpu(cpu, HK_TYPE_TICK)) {
+			cpu_32bit_unofflineable = cpu;
+			pr_info("Asymmetric 32-bit EL0 support detected on housekeeping CPU %u;"
+				"CPU hot-unplug disabled on CPU %u\n", cpu, cpu);
+		}
+		return 0;
+	}
+
 	if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit)
 		return 0;
 
-	if (cpu_32bit_unofflineable < 0)
-		return 0;
-
 	/*
-	 * We've detected a mismatch. We need to keep one of our CPUs with
-	 * 32-bit EL0 online so that is_cpu_allowed() doesn't end up rejecting
-	 * every CPU in the system for a 32-bit task.
+	 * We've detected a mismatch. We need to keep one of our CPUs, preferrably
+	 * housekeeping, with 32-bit EL0 online so that is_cpu_allowed() doesn't end up
+	 * rejecting every CPU in the system for a 32-bit task.
 	 */
-	cpu_32bit_unofflineable = cpu_32bit ? cpu : cpumask_any_and(cpu_32bit_el0_mask,
-								    cpu_active_mask);
+	cpu_32bit_unofflineable = cpumask_any_and(fallback_32bit_el0_mask, cpu_active_mask);
+	if (cpu_32bit_unofflineable >= nr_cpu_ids)
+		cpu_32bit_unofflineable = cpumask_any_and(cpu_32bit_el0_mask, cpu_active_mask);
+
 	setup_elf_hwcaps(compat_elf_hwcaps);
 	elf_hwcap_fixup();
 	pr_info("Asymmetric 32-bit EL0 support detected on CPU %u; CPU hot-unplug disabled on CPU %u\n",
@@ -3641,6 +3671,9 @@ static int __init init_32bit_el0_mask(void)
 	if (!zalloc_cpumask_var(&cpu_32bit_el0_mask, GFP_KERNEL))
 		return -ENOMEM;
 
+	if (!zalloc_cpumask_var(&fallback_32bit_el0_mask, GFP_KERNEL))
+		return -ENOMEM;
+
 	return cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 				 "arm64/mismatched_32bit_el0:online",
 				 mismatched_32bit_el0_online, mismatched_32bit_el0_offline);
diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h
index bbaec80c78c5..ac01dc4eb2ce 100644
--- a/include/linux/mmu_context.h
+++ b/include/linux/mmu_context.h
@@ -24,6 +24,7 @@ static inline void leave_mm(void) { }
 #ifndef task_cpu_possible_mask
 # define task_cpu_possible_mask(p)	cpu_possible_mask
 # define task_cpu_possible(cpu, p)	true
+# define task_cpu_fallback_mask(p)	housekeeping_cpumask(HK_TYPE_TICK)
 #else
 # define task_cpu_possible(cpu, p)	cpumask_test_cpu((cpu), task_cpu_possible_mask(p))
 #endif
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 719e0ed1e976..b4b9743d7c9c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3494,7 +3494,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
 			 *
 			 * More yuck to audit.
 			 */
-			do_set_cpus_allowed(p, task_cpu_possible_mask(p));
+			do_set_cpus_allowed(p, task_cpu_fallback_mask(p));
 			state = fail;
 			break;
 		case fail:
-- 
2.46.0

[PATCH 13/21] kthread: Make sure kthread hasn't started while binding it

[Frederic Weisbecker]

Make sure the kthread is sleeping in the schedule_preempt_disabled()
call before calling its handler when kthread_bind[_mask]() is called
on it. This provides a sanity check verifying that the task is not
randomly blocked later at some point within its function handler, in
which case it could be just concurrently awaken, leaving the call to
do_set_cpus_allowed() without any effect until the next voluntary sleep.

Rely on the wake-up ordering to ensure that the newly introduced "started"
field returns the expected value:

    TASK A                                   TASK B
    ------                                   ------
READ kthread->started
wake_up_process(B)
   rq_lock()
   ...
   rq_unlock() // RELEASE
                                           schedule()
                                              rq_lock() // ACQUIRE
                                              // schedule task B
                                              rq_unlock()
                                              WRITE kthread->started

Similarly, writing kthread->started before subsequent voluntary sleeps
will be visible after calling wait_task_inactive() in
__kthread_bind_mask(), reporting potential misuse of the API.

Upcoming patches will make further use of this facility.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/kthread.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 9bb36897b6c6..b9bdb21a0101 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -53,6 +53,7 @@ struct kthread_create_info
 struct kthread {
 	unsigned long flags;
 	unsigned int cpu;
+	int started;
 	int result;
 	int (*threadfn)(void *);
 	void *data;
@@ -382,6 +383,8 @@ static int kthread(void *_create)
 	schedule_preempt_disabled();
 	preempt_enable();
 
+	self->started = 1;
+
 	ret = -EINTR;
 	if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
 		cgroup_kthread_ready();
@@ -540,7 +543,9 @@ static void __kthread_bind(struct task_struct *p, unsigned int cpu, unsigned int
 
 void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
 {
+	struct kthread *kthread = to_kthread(p);
 	__kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
+	WARN_ON_ONCE(kthread->started);
 }
 
 /**
@@ -554,7 +559,9 @@ void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
  */
 void kthread_bind(struct task_struct *p, unsigned int cpu)
 {
+	struct kthread *kthread = to_kthread(p);
 	__kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
+	WARN_ON_ONCE(kthread->started);
 }
 EXPORT_SYMBOL(kthread_bind);
 
-- 
2.46.0

[PATCH 14/21] kthread: Default affine kthread to its preferred NUMA node

[Frederic Weisbecker]

Kthreads attached to a preferred NUMA node for their task structure
allocation can also be assumed to run preferrably within that same node.

A more precise affinity is usually notified by calling
kthread_create_on_cpu() or kthread_bind[_mask]() before the first wakeup.

For the others, a default affinity to the node is desired and sometimes
implemented with more or less success when it comes to deal with hotplug
events and nohz_full / CPU Isolation interactions:

- kcompactd is affine to its node and handles hotplug but not CPU Isolation
- kswapd is affine to its node and ignores hotplug and CPU Isolation
- A bunch of drivers create their kthreads on a specific node and
  don't take care about affining further.

Handle that default node affinity preference at the generic level
instead, provided a kthread is created on an actual node and doesn't
apply any specific affinity such as a given CPU or a custom cpumask to
bind to before its first wake-up.

This generic handling is aware of CPU hotplug events and CPU isolation
such that:

* When a housekeeping CPU goes up that is part of the node of a given
  kthread, the related task is re-affined to that own node if it was
  previously running on the default last resort online housekeeping set
  from other nodes.

* When a housekeeping CPU goes down while it was part of the node of a
  kthread, the running task is migrated (or the sleeping task is woken
  up) automatically by the scheduler to other housekeepers within the
  same node or, as a last resort, to all housekeepers from other nodes.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 include/linux/cpuhotplug.h |   1 +
 kernel/kthread.c           | 106 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 106 insertions(+), 1 deletion(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 2361ed4d2b15..228f27150a93 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -239,6 +239,7 @@ enum cpuhp_state {
 	CPUHP_AP_WORKQUEUE_ONLINE,
 	CPUHP_AP_RANDOM_ONLINE,
 	CPUHP_AP_RCUTREE_ONLINE,
+	CPUHP_AP_KTHREADS_ONLINE,
 	CPUHP_AP_BASE_CACHEINFO_ONLINE,
 	CPUHP_AP_ONLINE_DYN,
 	CPUHP_AP_ONLINE_DYN_END		= CPUHP_AP_ONLINE_DYN + 40,
diff --git a/kernel/kthread.c b/kernel/kthread.c
index b9bdb21a0101..df6a0551e8ba 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -35,6 +35,9 @@ static DEFINE_SPINLOCK(kthread_create_lock);
 static LIST_HEAD(kthread_create_list);
 struct task_struct *kthreadd_task;
 
+static LIST_HEAD(kthreads_hotplug);
+static DEFINE_MUTEX(kthreads_hotplug_lock);
+
 struct kthread_create_info
 {
 	/* Information passed to kthread() from kthreadd. */
@@ -53,6 +56,7 @@ struct kthread_create_info
 struct kthread {
 	unsigned long flags;
 	unsigned int cpu;
+	unsigned int node;
 	int started;
 	int result;
 	int (*threadfn)(void *);
@@ -64,6 +68,8 @@ struct kthread {
 #endif
 	/* To store the full name if task comm is truncated. */
 	char *full_name;
+	struct task_struct *task;
+	struct list_head hotplug_node;
 };
 
 enum KTHREAD_BITS {
@@ -122,8 +128,11 @@ bool set_kthread_struct(struct task_struct *p)
 
 	init_completion(&kthread->exited);
 	init_completion(&kthread->parked);
+	INIT_LIST_HEAD(&kthread->hotplug_node);
 	p->vfork_done = &kthread->exited;
 
+	kthread->task = p;
+	kthread->node = tsk_fork_get_node(current);
 	p->worker_private = kthread;
 	return true;
 }
@@ -314,6 +323,11 @@ void __noreturn kthread_exit(long result)
 {
 	struct kthread *kthread = to_kthread(current);
 	kthread->result = result;
+	if (!list_empty(&kthread->hotplug_node)) {
+		mutex_lock(&kthreads_hotplug_lock);
+		list_del(&kthread->hotplug_node);
+		mutex_unlock(&kthreads_hotplug_lock);
+	}
 	do_exit(0);
 }
 EXPORT_SYMBOL(kthread_exit);
@@ -339,6 +353,48 @@ void __noreturn kthread_complete_and_exit(struct completion *comp, long code)
 }
 EXPORT_SYMBOL(kthread_complete_and_exit);
 
+static void kthread_fetch_affinity(struct kthread *kthread, struct cpumask *cpumask)
+{
+	cpumask_and(cpumask, cpumask_of_node(kthread->node),
+		    housekeeping_cpumask(HK_TYPE_KTHREAD));
+
+	if (cpumask_empty(cpumask))
+		cpumask_copy(cpumask, housekeeping_cpumask(HK_TYPE_KTHREAD));
+}
+
+static void kthread_affine_node(void)
+{
+	struct kthread *kthread = to_kthread(current);
+	cpumask_var_t affinity;
+
+	WARN_ON_ONCE(kthread_is_per_cpu(current));
+
+	if (kthread->node == NUMA_NO_NODE) {
+		housekeeping_affine(current, HK_TYPE_RCU);
+	} else {
+		if (!zalloc_cpumask_var(&affinity, GFP_KERNEL)) {
+			WARN_ON_ONCE(1);
+			return;
+		}
+
+		mutex_lock(&kthreads_hotplug_lock);
+		WARN_ON_ONCE(!list_empty(&kthread->hotplug_node));
+		list_add_tail(&kthread->hotplug_node, &kthreads_hotplug);
+		/*
+		 * The node cpumask is racy when read from kthread() but:
+		 * - a racing CPU going down will either fail on the subsequent
+		 *   call to set_cpus_allowed_ptr() or be migrated to housekeepers
+		 *   afterwards by the scheduler.
+		 * - a racing CPU going up will be handled by kthreads_online_cpu()
+		 */
+		kthread_fetch_affinity(kthread, affinity);
+		set_cpus_allowed_ptr(current, affinity);
+		mutex_unlock(&kthreads_hotplug_lock);
+
+		free_cpumask_var(affinity);
+	}
+}
+
 static int kthread(void *_create)
 {
 	static const struct sched_param param = { .sched_priority = 0 };
@@ -369,7 +425,6 @@ static int kthread(void *_create)
 	 * back to default in case they have been changed.
 	 */
 	sched_setscheduler_nocheck(current, SCHED_NORMAL, &param);
-	set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_TYPE_KTHREAD));
 
 	/* OK, tell user we're spawned, wait for stop or wakeup */
 	__set_current_state(TASK_UNINTERRUPTIBLE);
@@ -385,6 +440,9 @@ static int kthread(void *_create)
 
 	self->started = 1;
 
+	if (!(current->flags & PF_NO_SETAFFINITY))
+		kthread_affine_node();
+
 	ret = -EINTR;
 	if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
 		cgroup_kthread_ready();
@@ -781,6 +839,52 @@ int kthreadd(void *unused)
 	return 0;
 }
 
+/*
+ * Re-affine kthreads according to their preferences
+ * and the newly online CPU. The CPU down part is handled
+ * by select_fallback_rq() which default re-affines to
+ * housekeepers in case the preferred affinity doesn't
+ * apply anymore.
+ */
+static int kthreads_online_cpu(unsigned int cpu)
+{
+	cpumask_var_t affinity;
+	struct kthread *k;
+	int ret;
+
+	guard(mutex)(&kthreads_hotplug_lock);
+
+	if (list_empty(&kthreads_hotplug))
+		return 0;
+
+	if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
+		return -ENOMEM;
+
+	ret = 0;
+
+	list_for_each_entry(k, &kthreads_hotplug, hotplug_node) {
+		if (WARN_ON_ONCE((k->task->flags & PF_NO_SETAFFINITY) ||
+				 kthread_is_per_cpu(k->task) ||
+				 k->node == NUMA_NO_NODE)) {
+			ret = -EINVAL;
+			continue;
+		}
+		kthread_fetch_affinity(k, affinity);
+		set_cpus_allowed_ptr(k->task, affinity);
+	}
+
+	free_cpumask_var(affinity);
+
+	return ret;
+}
+
+static int kthreads_init(void)
+{
+	return cpuhp_setup_state(CPUHP_AP_KTHREADS_ONLINE, "kthreads:online",
+				kthreads_online_cpu, NULL);
+}
+early_initcall(kthreads_init);
+
 void __kthread_init_worker(struct kthread_worker *worker,
 				const char *name,
 				struct lock_class_key *key)
-- 
2.46.0

[PATCH 15/21] mm: Create/affine kcompactd to its preferred node

[Frederic Weisbecker]

Kcompactd is dedicated to a specific node. As such it wants to be
preferrably affine to it, memory and CPUs-wise.

Use the proper kthread API to achieve that. As a bonus it takes care of
CPU-hotplug events and CPU-isolation on its behalf.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 mm/compaction.c | 43 +++----------------------------------------
 1 file changed, 3 insertions(+), 40 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index a2b16b08cbbf..a31c0f5758cf 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -3154,15 +3154,9 @@ void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
 static int kcompactd(void *p)
 {
 	pg_data_t *pgdat = (pg_data_t *)p;
-	struct task_struct *tsk = current;
 	long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC);
 	long timeout = default_timeout;
 
-	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
-
-	if (!cpumask_empty(cpumask))
-		set_cpus_allowed_ptr(tsk, cpumask);
-
 	set_freezable();
 
 	pgdat->kcompactd_max_order = 0;
@@ -3233,10 +3227,12 @@ void __meminit kcompactd_run(int nid)
 	if (pgdat->kcompactd)
 		return;
 
-	pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
+	pgdat->kcompactd = kthread_create_on_node(kcompactd, pgdat, nid, "kcompactd%d", nid);
 	if (IS_ERR(pgdat->kcompactd)) {
 		pr_err("Failed to start kcompactd on node %d\n", nid);
 		pgdat->kcompactd = NULL;
+	} else {
+		wake_up_process(pgdat->kcompactd);
 	}
 }
 
@@ -3254,30 +3250,6 @@ void __meminit kcompactd_stop(int nid)
 	}
 }
 
-/*
- * It's optimal to keep kcompactd on the same CPUs as their memory, but
- * not required for correctness. So if the last cpu in a node goes
- * away, we get changed to run anywhere: as the first one comes back,
- * restore their cpu bindings.
- */
-static int kcompactd_cpu_online(unsigned int cpu)
-{
-	int nid;
-
-	for_each_node_state(nid, N_MEMORY) {
-		pg_data_t *pgdat = NODE_DATA(nid);
-		const struct cpumask *mask;
-
-		mask = cpumask_of_node(pgdat->node_id);
-
-		if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
-			/* One of our CPUs online: restore mask */
-			if (pgdat->kcompactd)
-				set_cpus_allowed_ptr(pgdat->kcompactd, mask);
-	}
-	return 0;
-}
-
 static int proc_dointvec_minmax_warn_RT_change(const struct ctl_table *table,
 		int write, void *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -3337,15 +3309,6 @@ static struct ctl_table vm_compaction[] = {
 static int __init kcompactd_init(void)
 {
 	int nid;
-	int ret;
-
-	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
-					"mm/compaction:online",
-					kcompactd_cpu_online, NULL);
-	if (ret < 0) {
-		pr_err("kcompactd: failed to register hotplug callbacks.\n");
-		return ret;
-	}
 
 	for_each_node_state(nid, N_MEMORY)
 		kcompactd_run(nid);
-- 
2.46.0

[PATCH 16/21] mm: Create/affine kswapd to its preferred node

[Frederic Weisbecker]

kswapd is dedicated to a specific node. As such it wants to be
preferrably affine to it, memory and CPUs-wise.

Use the proper kthread API to achieve that. As a bonus it takes care of
CPU-hotplug events and CPU-isolation on its behalf.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 mm/vmscan.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 28ba2b06fc7d..5d7686bef51c 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -7168,10 +7168,6 @@ static int kswapd(void *p)
 	unsigned int highest_zoneidx = MAX_NR_ZONES - 1;
 	pg_data_t *pgdat = (pg_data_t *)p;
 	struct task_struct *tsk = current;
-	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
-
-	if (!cpumask_empty(cpumask))
-		set_cpus_allowed_ptr(tsk, cpumask);
 
 	/*
 	 * Tell the memory management that we're a "memory allocator",
@@ -7340,13 +7336,15 @@ void __meminit kswapd_run(int nid)
 
 	pgdat_kswapd_lock(pgdat);
 	if (!pgdat->kswapd) {
-		pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
+		pgdat->kswapd = kthread_create_on_node(kswapd, pgdat, nid, "kswapd%d", nid);
 		if (IS_ERR(pgdat->kswapd)) {
 			/* failure at boot is fatal */
 			pr_err("Failed to start kswapd on node %d，ret=%ld\n",
 				   nid, PTR_ERR(pgdat->kswapd));
 			BUG_ON(system_state < SYSTEM_RUNNING);
 			pgdat->kswapd = NULL;
+		} else {
+			wake_up_process(pgdat->kswapd);
 		}
 	}
 	pgdat_kswapd_unlock(pgdat);
-- 
2.46.0

[PATCH 17/21] kthread: Implement preferred affinity

[Frederic Weisbecker]

Affining kthreads follow either of four existing different patterns:

1) Per-CPU kthreads must stay affine to a single CPU and never execute
   relevant code on any other CPU. This is currently handled by smpboot
   code which takes care of CPU-hotplug operations.

2) Kthreads that _have_ to be affine to a specific set of CPUs and can't
   run anywhere else. The affinity is set through kthread_bind_mask()
   and the subsystem takes care by itself to handle CPU-hotplug operations.

3) Kthreads that prefer to be affine to a specific NUMA node. That
   preferred affinity is applied by default when an actual node ID is
   passed on kthread creation, provided the kthread is not per-CPU and
   no call to kthread_bind_mask() has been issued before the first
   wake-up.

4) Similar to the previous point but kthreads have a preferred affinity
   different than a node. It is set manually like any other task and
   CPU-hotplug is supposed to be handled by the relevant subsystem so
   that the task is properly reaffined whenever a given CPU from the
   preferred affinity comes up. Also care must be taken so that the
   preferred affinity doesn't cross housekeeping cpumask boundaries.

Provide a function to handle the last usecase, mostly reusing the
current node default affinity infrastructure. kthread_affine_preferred()
is introduced, to be used just like kthread_bind_mask(), right after
kthread creation and before the first wake up. The kthread is then
affine right away to the cpumask passed through the API if it has online
housekeeping CPUs. Otherwise it will be affine to all online
housekeeping CPUs as a last resort.

As with node affinity, it is aware of CPU hotplug events such that:

* When a housekeeping CPU goes up that is part of the preferred affinity
  of a given kthread, the related task is re-affined to that preferred
  affinity if it was previously running on the default last resort
  online housekeeping set.

* When a housekeeping CPU goes down while it was part of the preferred
  affinity of a kthread, the running task is migrated (or the sleeping
  task is woken up) automatically by the scheduler to other housekeepers
  within the preferred affinity or, as a last resort, to all
  housekeepers from other nodes.

Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 include/linux/kthread.h |  1 +
 kernel/kthread.c        | 68 ++++++++++++++++++++++++++++++++++++-----
 2 files changed, 62 insertions(+), 7 deletions(-)

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index b11f53c1ba2e..30209bdf83a2 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -85,6 +85,7 @@ kthread_run_on_cpu(int (*threadfn)(void *data), void *data,
 void free_kthread_struct(struct task_struct *k);
 void kthread_bind(struct task_struct *k, unsigned int cpu);
 void kthread_bind_mask(struct task_struct *k, const struct cpumask *mask);
+int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask);
 int kthread_stop(struct task_struct *k);
 int kthread_stop_put(struct task_struct *k);
 bool kthread_should_stop(void);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index df6a0551e8ba..43724fc6e021 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -70,6 +70,7 @@ struct kthread {
 	char *full_name;
 	struct task_struct *task;
 	struct list_head hotplug_node;
+	struct cpumask *preferred_affinity;
 };
 
 enum KTHREAD_BITS {
@@ -327,6 +328,11 @@ void __noreturn kthread_exit(long result)
 		mutex_lock(&kthreads_hotplug_lock);
 		list_del(&kthread->hotplug_node);
 		mutex_unlock(&kthreads_hotplug_lock);
+
+		if (kthread->preferred_affinity) {
+			kfree(kthread->preferred_affinity);
+			kthread->preferred_affinity = NULL;
+		}
 	}
 	do_exit(0);
 }
@@ -355,9 +361,17 @@ EXPORT_SYMBOL(kthread_complete_and_exit);
 
 static void kthread_fetch_affinity(struct kthread *kthread, struct cpumask *cpumask)
 {
-	cpumask_and(cpumask, cpumask_of_node(kthread->node),
-		    housekeeping_cpumask(HK_TYPE_KTHREAD));
+	const struct cpumask *pref;
 
+	if (kthread->preferred_affinity) {
+		pref = kthread->preferred_affinity;
+	} else {
+		if (WARN_ON_ONCE(kthread->node == NUMA_NO_NODE))
+			return;
+		pref = cpumask_of_node(kthread->node);
+	}
+
+	cpumask_and(cpumask, pref, housekeeping_cpumask(HK_TYPE_KTHREAD));
 	if (cpumask_empty(cpumask))
 		cpumask_copy(cpumask, housekeeping_cpumask(HK_TYPE_KTHREAD));
 }
@@ -440,7 +454,7 @@ static int kthread(void *_create)
 
 	self->started = 1;
 
-	if (!(current->flags & PF_NO_SETAFFINITY))
+	if (!(current->flags & PF_NO_SETAFFINITY) && !self->preferred_affinity)
 		kthread_affine_node();
 
 	ret = -EINTR;
@@ -839,12 +853,53 @@ int kthreadd(void *unused)
 	return 0;
 }
 
+int kthread_affine_preferred(struct task_struct *p, const struct cpumask *mask)
+{
+	struct kthread *kthread = to_kthread(p);
+	cpumask_var_t affinity;
+	unsigned long flags;
+	int ret;
+
+	if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE) || kthread->started) {
+		WARN_ON(1);
+		return -EINVAL;
+	}
+
+	WARN_ON_ONCE(kthread->preferred_affinity);
+
+	if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
+		return -ENOMEM;
+
+	kthread->preferred_affinity = kzalloc(sizeof(struct cpumask), GFP_KERNEL);
+	if (!kthread->preferred_affinity) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	mutex_lock(&kthreads_hotplug_lock);
+	cpumask_copy(kthread->preferred_affinity, mask);
+	WARN_ON_ONCE(!list_empty(&kthread->hotplug_node));
+	list_add_tail(&kthread->hotplug_node, &kthreads_hotplug);
+	kthread_fetch_affinity(kthread, affinity);
+
+	/* It's safe because the task is inactive. */
+	raw_spin_lock_irqsave(&p->pi_lock, flags);
+	do_set_cpus_allowed(p, affinity);
+	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+
+	mutex_unlock(&kthreads_hotplug_lock);
+out:
+	free_cpumask_var(affinity);
+
+	return 0;
+}
+
 /*
  * Re-affine kthreads according to their preferences
  * and the newly online CPU. The CPU down part is handled
  * by select_fallback_rq() which default re-affines to
- * housekeepers in case the preferred affinity doesn't
- * apply anymore.
+ * housekeepers from other nodes in case the preferred
+ * affinity doesn't apply anymore.
  */
 static int kthreads_online_cpu(unsigned int cpu)
 {
@@ -864,8 +919,7 @@ static int kthreads_online_cpu(unsigned int cpu)
 
 	list_for_each_entry(k, &kthreads_hotplug, hotplug_node) {
 		if (WARN_ON_ONCE((k->task->flags & PF_NO_SETAFFINITY) ||
-				 kthread_is_per_cpu(k->task) ||
-				 k->node == NUMA_NO_NODE)) {
+				 kthread_is_per_cpu(k->task))) {
 			ret = -EINVAL;
 			continue;
 		}
-- 
2.46.0

[PATCH 18/21] rcu: Use kthread preferred affinity for RCU boost

[Frederic Weisbecker]

Now that kthreads have an infrastructure to handle preferred affinity
against CPU hotplug and housekeeping cpumask, convert RCU boost to use
it instead of handling all the constraints by itself.

Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/rcu/tree.c        | 27 +++++++++++++++++++--------
 kernel/rcu/tree_plugin.h | 11 ++---------
 2 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b1f883fcd918..c9fd28f0f068 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -149,7 +149,6 @@ static int rcu_scheduler_fully_active __read_mostly;
 
 static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
 			      unsigned long gps, unsigned long flags);
-static struct task_struct *rcu_boost_task(struct rcu_node *rnp);
 static void invoke_rcu_core(void);
 static void rcu_report_exp_rdp(struct rcu_data *rdp);
 static void sync_sched_exp_online_cleanup(int cpu);
@@ -5008,6 +5007,22 @@ int rcutree_prepare_cpu(unsigned int cpu)
 	return 0;
 }
 
+static void rcu_thread_affine_rnp(struct task_struct *t, struct rcu_node *rnp)
+{
+	cpumask_var_t affinity;
+	int cpu;
+
+	if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
+		return;
+
+	for_each_leaf_node_possible_cpu(rnp, cpu)
+		cpumask_set_cpu(cpu, affinity);
+
+	kthread_affine_preferred(t, affinity);
+
+	free_cpumask_var(affinity);
+}
+
 /*
  * Update kthreads affinity during CPU-hotplug changes.
  *
@@ -5027,19 +5042,18 @@ static void rcutree_affinity_setting(unsigned int cpu, int outgoingcpu)
 	unsigned long mask;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
-	struct task_struct *task_boost, *task_exp;
+	struct task_struct *task_exp;
 
 	rdp = per_cpu_ptr(&rcu_data, cpu);
 	rnp = rdp->mynode;
 
-	task_boost = rcu_boost_task(rnp);
 	task_exp = rcu_exp_par_gp_task(rnp);
 
 	/*
-	 * If CPU is the boot one, those tasks are created later from early
+	 * If CPU is the boot one, this task is created later from early
 	 * initcall since kthreadd must be created first.
 	 */
-	if (!task_boost && !task_exp)
+	if (!task_exp)
 		return;
 
 	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
@@ -5061,9 +5075,6 @@ static void rcutree_affinity_setting(unsigned int cpu, int outgoingcpu)
 	if (task_exp)
 		set_cpus_allowed_ptr(task_exp, cm);
 
-	if (task_boost)
-		set_cpus_allowed_ptr(task_boost, cm);
-
 	mutex_unlock(&rnp->kthread_mutex);
 
 	free_cpumask_var(cm);
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1c7cbd145d5e..223f3a02351e 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1217,16 +1217,13 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 	raw_spin_lock_irqsave_rcu_node(rnp, flags);
 	rnp->boost_kthread_task = t;
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
 	sp.sched_priority = kthread_prio;
 	sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+	rcu_thread_affine_rnp(t, rnp);
 	wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
 }
 
-static struct task_struct *rcu_boost_task(struct rcu_node *rnp)
-{
-	return READ_ONCE(rnp->boost_kthread_task);
-}
-
 #else /* #ifdef CONFIG_RCU_BOOST */
 
 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
@@ -1243,10 +1240,6 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
 {
 }
 
-static struct task_struct *rcu_boost_task(struct rcu_node *rnp)
-{
-	return NULL;
-}
 #endif /* #else #ifdef CONFIG_RCU_BOOST */
 
 /*
-- 
2.46.0

[PATCH 19/21] kthread: Unify kthread_create_on_cpu() and kthread_create_worker_on_cpu() automatic format

[Frederic Weisbecker]

kthread_create_on_cpu() uses the CPU argument as an implicit and unique
printf argument to add to the format whereas
kthread_create_worker_on_cpu() still relies on explicitly passing the
printf arguments. This difference in behaviour is error prone and
doesn't help standardizing per-CPU kthread names.

Unify the behaviours and convert kthread_create_worker_on_cpu() to
use the printf behaviour of kthread_create_on_cpu().

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 fs/erofs/zdata.c        |  2 +-
 include/linux/kthread.h | 21 +++++++++++----
 kernel/kthread.c        | 59 ++++++++++++++++++++++++-----------------
 3 files changed, 52 insertions(+), 30 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index a569ff9dfd04..e4b5c56a7516 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -318,7 +318,7 @@ static void erofs_destroy_percpu_workers(void)
 static struct kthread_worker *erofs_init_percpu_worker(int cpu)
 {
 	struct kthread_worker *worker =
-		kthread_create_worker_on_cpu(cpu, 0, "erofs_worker/%u", cpu);
+		kthread_create_worker_on_cpu(cpu, 0, "erofs_worker/%u");
 
 	if (IS_ERR(worker))
 		return worker;
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 30209bdf83a2..0c66e7c1092a 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -187,13 +187,24 @@ extern void __kthread_init_worker(struct kthread_worker *worker,
 
 int kthread_worker_fn(void *worker_ptr);
 
-__printf(2, 3)
+__printf(3, 4)
+struct kthread_worker *kthread_create_worker_on_node(unsigned int flags,
+						     int node,
+						     const char namefmt[], ...);
+
+#define kthread_create_worker(flags, namefmt, ...) \
+({									   \
+	struct kthread_worker *__kw					   \
+		= kthread_create_worker_on_node(flags, NUMA_NO_NODE,	   \
+						namefmt, ## __VA_ARGS__);  \
+	if (!IS_ERR(__kw))						   \
+		wake_up_process(__kw->task);				   \
+	__kw;								   \
+})
+
 struct kthread_worker *
-kthread_create_worker(unsigned int flags, const char namefmt[], ...);
-
-__printf(3, 4) struct kthread_worker *
 kthread_create_worker_on_cpu(int cpu, unsigned int flags,
-			     const char namefmt[], ...);
+			     const char namefmt[]);
 
 bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 43724fc6e021..409732fba736 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1030,12 +1030,11 @@ int kthread_worker_fn(void *worker_ptr)
 EXPORT_SYMBOL_GPL(kthread_worker_fn);
 
 static __printf(3, 0) struct kthread_worker *
-__kthread_create_worker(int cpu, unsigned int flags,
-			const char namefmt[], va_list args)
+__kthread_create_worker_on_node(unsigned int flags, int node,
+				const char namefmt[], va_list args)
 {
 	struct kthread_worker *worker;
 	struct task_struct *task;
-	int node = NUMA_NO_NODE;
 
 	worker = kzalloc(sizeof(*worker), GFP_KERNEL);
 	if (!worker)
@@ -1043,20 +1042,14 @@ __kthread_create_worker(int cpu, unsigned int flags,
 
 	kthread_init_worker(worker);
 
-	if (cpu >= 0)
-		node = cpu_to_node(cpu);
-
 	task = __kthread_create_on_node(kthread_worker_fn, worker,
-						node, namefmt, args);
+					node, namefmt, args);
 	if (IS_ERR(task))
 		goto fail_task;
 
-	if (cpu >= 0)
-		kthread_bind(task, cpu);
-
 	worker->flags = flags;
 	worker->task = task;
-	wake_up_process(task);
+
 	return worker;
 
 fail_task:
@@ -1067,6 +1060,7 @@ __kthread_create_worker(int cpu, unsigned int flags,
 /**
  * kthread_create_worker - create a kthread worker
  * @flags: flags modifying the default behavior of the worker
+ * @node: task structure for the thread is allocated on this node
  * @namefmt: printf-style name for the kthread worker (task).
  *
  * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
@@ -1074,25 +1068,49 @@ __kthread_create_worker(int cpu, unsigned int flags,
  * when the caller was killed by a fatal signal.
  */
 struct kthread_worker *
-kthread_create_worker(unsigned int flags, const char namefmt[], ...)
+kthread_create_worker_on_node(unsigned int flags, int node, const char namefmt[], ...)
 {
 	struct kthread_worker *worker;
 	va_list args;
 
 	va_start(args, namefmt);
-	worker = __kthread_create_worker(-1, flags, namefmt, args);
+	worker = __kthread_create_worker_on_node(flags, node, namefmt, args);
 	va_end(args);
 
+	if (worker)
+		wake_up_process(worker->task);
+
+	return worker;
+}
+EXPORT_SYMBOL(kthread_create_worker_on_node);
+
+static __printf(3, 4) struct kthread_worker *
+__kthread_create_worker_on_cpu(int cpu, unsigned int flags,
+			       const char namefmt[], ...)
+{
+	struct kthread_worker *worker;
+	va_list args;
+
+	va_start(args, namefmt);
+	worker = __kthread_create_worker_on_node(flags, cpu_to_node(cpu),
+						 namefmt, args);
+	va_end(args);
+
+	if (worker) {
+		kthread_bind(worker->task, cpu);
+		wake_up_process(worker->task);
+	}
+
 	return worker;
 }
-EXPORT_SYMBOL(kthread_create_worker);
 
 /**
  * kthread_create_worker_on_cpu - create a kthread worker and bind it
  *	to a given CPU and the associated NUMA node.
  * @cpu: CPU number
  * @flags: flags modifying the default behavior of the worker
- * @namefmt: printf-style name for the kthread worker (task).
+ * @namefmt: printf-style name for the thread. Format is restricted
+ *	     to "name.*%u". Code fills in cpu number.
  *
  * Use a valid CPU number if you want to bind the kthread worker
  * to the given CPU and the associated NUMA node.
@@ -1124,16 +1142,9 @@ EXPORT_SYMBOL(kthread_create_worker);
  */
 struct kthread_worker *
 kthread_create_worker_on_cpu(int cpu, unsigned int flags,
-			     const char namefmt[], ...)
+			     const char namefmt[])
 {
-	struct kthread_worker *worker;
-	va_list args;
-
-	va_start(args, namefmt);
-	worker = __kthread_create_worker(cpu, flags, namefmt, args);
-	va_end(args);
-
-	return worker;
+	return __kthread_create_worker_on_cpu(cpu, flags, namefmt, cpu);
 }
 EXPORT_SYMBOL(kthread_create_worker_on_cpu);
 
-- 
2.46.0

[PATCH 20/21] treewide: Introduce kthread_run_worker[_on_cpu]()

[Frederic Weisbecker]

kthread_create() creates a kthread without running it yet. kthread_run()
creates a kthread and runs it.

On the other hand, kthread_create_worker() creates a kthread worker and
runs it.

This difference in behaviours is confusing. Also there is no way to
create a kthread worker and affine it using kthread_bind_mask() or
kthread_affine_preferred() before starting it.

Consolidate the behaviours and introduce kthread_run_worker[_on_cpu]()
that behaves just like kthread_run(). kthread_create_worker[_on_cpu]()
will now only create a kthread worker without starting it.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 arch/x86/kvm/i8254.c                          |  2 +-
 crypto/crypto_engine.c                        |  2 +-
 drivers/cpufreq/cppc_cpufreq.c                |  2 +-
 drivers/gpu/drm/drm_vblank_work.c             |  2 +-
 .../drm/i915/gem/selftests/i915_gem_context.c |  2 +-
 drivers/gpu/drm/i915/gt/selftest_execlists.c  |  2 +-
 drivers/gpu/drm/i915/gt/selftest_hangcheck.c  |  2 +-
 drivers/gpu/drm/i915/gt/selftest_slpc.c       |  2 +-
 drivers/gpu/drm/i915/selftests/i915_request.c |  8 ++--
 drivers/gpu/drm/msm/disp/msm_disp_snapshot.c  |  2 +-
 drivers/gpu/drm/msm/msm_atomic.c              |  2 +-
 drivers/gpu/drm/msm/msm_gpu.c                 |  2 +-
 drivers/gpu/drm/msm/msm_kms.c                 |  2 +-
 .../platform/chips-media/wave5/wave5-vpu.c    |  2 +-
 drivers/net/dsa/mv88e6xxx/chip.c              |  2 +-
 drivers/net/ethernet/intel/ice/ice_dpll.c     |  2 +-
 drivers/net/ethernet/intel/ice/ice_gnss.c     |  2 +-
 drivers/net/ethernet/intel/ice/ice_ptp.c      |  2 +-
 drivers/platform/chrome/cros_ec_spi.c         |  2 +-
 drivers/ptp/ptp_clock.c                       |  2 +-
 drivers/spi/spi.c                             |  2 +-
 drivers/usb/typec/tcpm/tcpm.c                 |  2 +-
 drivers/vdpa/vdpa_sim/vdpa_sim.c              |  2 +-
 drivers/watchdog/watchdog_dev.c               |  2 +-
 fs/erofs/zdata.c                              |  2 +-
 include/linux/kthread.h                       | 48 ++++++++++++++++---
 kernel/kthread.c                              | 31 +++---------
 kernel/rcu/tree.c                             |  4 +-
 kernel/sched/ext.c                            |  2 +-
 kernel/workqueue.c                            |  2 +-
 net/dsa/tag_ksz.c                             |  2 +-
 net/dsa/tag_ocelot_8021q.c                    |  2 +-
 net/dsa/tag_sja1105.c                         |  2 +-
 33 files changed, 83 insertions(+), 66 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index cd57a517d04a..d7ab8780ab9e 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -681,7 +681,7 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	pid_nr = pid_vnr(pid);
 	put_pid(pid);
 
-	pit->worker = kthread_create_worker(0, "kvm-pit/%d", pid_nr);
+	pit->worker = kthread_run_worker(0, "kvm-pit/%d", pid_nr);
 	if (IS_ERR(pit->worker))
 		goto fail_kthread;
 
diff --git a/crypto/crypto_engine.c b/crypto/crypto_engine.c
index e60a0eb628e8..c7c16da5e649 100644
--- a/crypto/crypto_engine.c
+++ b/crypto/crypto_engine.c
@@ -517,7 +517,7 @@ struct crypto_engine *crypto_engine_alloc_init_and_set(struct device *dev,
 	crypto_init_queue(&engine->queue, qlen);
 	spin_lock_init(&engine->queue_lock);
 
-	engine->kworker = kthread_create_worker(0, "%s", engine->name);
+	engine->kworker = kthread_run_worker(0, "%s", engine->name);
 	if (IS_ERR(engine->kworker)) {
 		dev_err(dev, "failed to create crypto request pump task\n");
 		return NULL;
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 2b8708475ac7..d265c0e060fd 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -241,7 +241,7 @@ static void __init cppc_freq_invariance_init(void)
 	if (fie_disabled)
 		return;
 
-	kworker_fie = kthread_create_worker(0, "cppc_fie");
+	kworker_fie = kthread_run_worker(0, "cppc_fie");
 	if (IS_ERR(kworker_fie)) {
 		pr_warn("%s: failed to create kworker_fie: %ld\n", __func__,
 			PTR_ERR(kworker_fie));
diff --git a/drivers/gpu/drm/drm_vblank_work.c b/drivers/gpu/drm/drm_vblank_work.c
index 1752ffb44e1d..9cc71120246f 100644
--- a/drivers/gpu/drm/drm_vblank_work.c
+++ b/drivers/gpu/drm/drm_vblank_work.c
@@ -277,7 +277,7 @@ int drm_vblank_worker_init(struct drm_vblank_crtc *vblank)
 
 	INIT_LIST_HEAD(&vblank->pending_work);
 	init_waitqueue_head(&vblank->work_wait_queue);
-	worker = kthread_create_worker(0, "card%d-crtc%d",
+	worker = kthread_run_worker(0, "card%d-crtc%d",
 				       vblank->dev->primary->index,
 				       vblank->pipe);
 	if (IS_ERR(worker))
diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
index 89d4dc8b60c6..eb0158e43417 100644
--- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c
@@ -369,7 +369,7 @@ static int live_parallel_switch(void *arg)
 		if (!data[n].ce[0])
 			continue;
 
-		worker = kthread_create_worker(0, "igt/parallel:%s",
+		worker = kthread_run_worker(0, "igt/parallel:%s",
 					       data[n].ce[0]->engine->name);
 		if (IS_ERR(worker)) {
 			err = PTR_ERR(worker);
diff --git a/drivers/gpu/drm/i915/gt/selftest_execlists.c b/drivers/gpu/drm/i915/gt/selftest_execlists.c
index 222ca7c44951..81c31396eceb 100644
--- a/drivers/gpu/drm/i915/gt/selftest_execlists.c
+++ b/drivers/gpu/drm/i915/gt/selftest_execlists.c
@@ -3574,7 +3574,7 @@ static int smoke_crescendo(struct preempt_smoke *smoke, unsigned int flags)
 			arg[id].batch = NULL;
 		arg[id].count = 0;
 
-		worker[id] = kthread_create_worker(0, "igt/smoke:%d", id);
+		worker[id] = kthread_run_worker(0, "igt/smoke:%d", id);
 		if (IS_ERR(worker[id])) {
 			err = PTR_ERR(worker[id]);
 			break;
diff --git a/drivers/gpu/drm/i915/gt/selftest_hangcheck.c b/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
index 9ce8ff1c04fe..9d3aeb237295 100644
--- a/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
+++ b/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
@@ -1025,7 +1025,7 @@ static int __igt_reset_engines(struct intel_gt *gt,
 			threads[tmp].engine = other;
 			threads[tmp].flags = flags;
 
-			worker = kthread_create_worker(0, "igt/%s",
+			worker = kthread_run_worker(0, "igt/%s",
 						       other->name);
 			if (IS_ERR(worker)) {
 				err = PTR_ERR(worker);
diff --git a/drivers/gpu/drm/i915/gt/selftest_slpc.c b/drivers/gpu/drm/i915/gt/selftest_slpc.c
index 4ecc4ae74a54..e218b229681f 100644
--- a/drivers/gpu/drm/i915/gt/selftest_slpc.c
+++ b/drivers/gpu/drm/i915/gt/selftest_slpc.c
@@ -489,7 +489,7 @@ static int live_slpc_tile_interaction(void *arg)
 		return -ENOMEM;
 
 	for_each_gt(gt, i915, i) {
-		threads[i].worker = kthread_create_worker(0, "igt/slpc_parallel:%d", gt->info.id);
+		threads[i].worker = kthread_run_worker(0, "igt/slpc_parallel:%d", gt->info.id);
 
 		if (IS_ERR(threads[i].worker)) {
 			ret = PTR_ERR(threads[i].worker);
diff --git a/drivers/gpu/drm/i915/selftests/i915_request.c b/drivers/gpu/drm/i915/selftests/i915_request.c
index acae30a04a94..88870844b5bd 100644
--- a/drivers/gpu/drm/i915/selftests/i915_request.c
+++ b/drivers/gpu/drm/i915/selftests/i915_request.c
@@ -492,7 +492,7 @@ static int mock_breadcrumbs_smoketest(void *arg)
 	for (n = 0; n < ncpus; n++) {
 		struct kthread_worker *worker;
 
-		worker = kthread_create_worker(0, "igt/%d", n);
+		worker = kthread_run_worker(0, "igt/%d", n);
 		if (IS_ERR(worker)) {
 			ret = PTR_ERR(worker);
 			ncpus = n;
@@ -1645,7 +1645,7 @@ static int live_parallel_engines(void *arg)
 		for_each_uabi_engine(engine, i915) {
 			struct kthread_worker *worker;
 
-			worker = kthread_create_worker(0, "igt/parallel:%s",
+			worker = kthread_run_worker(0, "igt/parallel:%s",
 						       engine->name);
 			if (IS_ERR(worker)) {
 				err = PTR_ERR(worker);
@@ -1806,7 +1806,7 @@ static int live_breadcrumbs_smoketest(void *arg)
 			unsigned int i = idx * ncpus + n;
 			struct kthread_worker *worker;
 
-			worker = kthread_create_worker(0, "igt/%d.%d", idx, n);
+			worker = kthread_run_worker(0, "igt/%d.%d", idx, n);
 			if (IS_ERR(worker)) {
 				ret = PTR_ERR(worker);
 				goto out_flush;
@@ -3219,7 +3219,7 @@ static int perf_parallel_engines(void *arg)
 
 			memset(&engines[idx].p, 0, sizeof(engines[idx].p));
 
-			worker = kthread_create_worker(0, "igt:%s",
+			worker = kthread_run_worker(0, "igt:%s",
 						       engine->name);
 			if (IS_ERR(worker)) {
 				err = PTR_ERR(worker);
diff --git a/drivers/gpu/drm/msm/disp/msm_disp_snapshot.c b/drivers/gpu/drm/msm/disp/msm_disp_snapshot.c
index e75b97127c0d..2be00b11e557 100644
--- a/drivers/gpu/drm/msm/disp/msm_disp_snapshot.c
+++ b/drivers/gpu/drm/msm/disp/msm_disp_snapshot.c
@@ -109,7 +109,7 @@ int msm_disp_snapshot_init(struct drm_device *drm_dev)
 
 	mutex_init(&kms->dump_mutex);
 
-	kms->dump_worker = kthread_create_worker(0, "%s", "disp_snapshot");
+	kms->dump_worker = kthread_run_worker(0, "%s", "disp_snapshot");
 	if (IS_ERR(kms->dump_worker))
 		DRM_ERROR("failed to create disp state task\n");
 
diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
index 9c45d641b521..a7a2384044ff 100644
--- a/drivers/gpu/drm/msm/msm_atomic.c
+++ b/drivers/gpu/drm/msm/msm_atomic.c
@@ -115,7 +115,7 @@ int msm_atomic_init_pending_timer(struct msm_pending_timer *timer,
 	timer->kms = kms;
 	timer->crtc_idx = crtc_idx;
 
-	timer->worker = kthread_create_worker(0, "atomic-worker-%d", crtc_idx);
+	timer->worker = kthread_run_worker(0, "atomic-worker-%d", crtc_idx);
 	if (IS_ERR(timer->worker)) {
 		int ret = PTR_ERR(timer->worker);
 		timer->worker = NULL;
diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
index a274b8466423..15f74e9dfc9e 100644
--- a/drivers/gpu/drm/msm/msm_gpu.c
+++ b/drivers/gpu/drm/msm/msm_gpu.c
@@ -859,7 +859,7 @@ int msm_gpu_init(struct drm_device *drm, struct platform_device *pdev,
 	gpu->funcs = funcs;
 	gpu->name = name;
 
-	gpu->worker = kthread_create_worker(0, "gpu-worker");
+	gpu->worker = kthread_run_worker(0, "gpu-worker");
 	if (IS_ERR(gpu->worker)) {
 		ret = PTR_ERR(gpu->worker);
 		gpu->worker = NULL;
diff --git a/drivers/gpu/drm/msm/msm_kms.c b/drivers/gpu/drm/msm/msm_kms.c
index af6a6fcb1173..8db9f3afb8ac 100644
--- a/drivers/gpu/drm/msm/msm_kms.c
+++ b/drivers/gpu/drm/msm/msm_kms.c
@@ -269,7 +269,7 @@ int msm_drm_kms_init(struct device *dev, const struct drm_driver *drv)
 		/* initialize event thread */
 		ev_thread = &priv->event_thread[drm_crtc_index(crtc)];
 		ev_thread->dev = ddev;
-		ev_thread->worker = kthread_create_worker(0, "crtc_event:%d", crtc->base.id);
+		ev_thread->worker = kthread_run_worker(0, "crtc_event:%d", crtc->base.id);
 		if (IS_ERR(ev_thread->worker)) {
 			ret = PTR_ERR(ev_thread->worker);
 			DRM_DEV_ERROR(dev, "failed to create crtc_event kthread\n");
diff --git a/drivers/media/platform/chips-media/wave5/wave5-vpu.c b/drivers/media/platform/chips-media/wave5/wave5-vpu.c
index 7273254ecb03..c49f5ed461cf 100644
--- a/drivers/media/platform/chips-media/wave5/wave5-vpu.c
+++ b/drivers/media/platform/chips-media/wave5/wave5-vpu.c
@@ -231,7 +231,7 @@ static int wave5_vpu_probe(struct platform_device *pdev)
 		dev_err(&pdev->dev, "failed to get irq resource, falling back to polling\n");
 		hrtimer_init(&dev->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_PINNED);
 		dev->hrtimer.function = &wave5_vpu_timer_callback;
-		dev->worker = kthread_create_worker(0, "vpu_irq_thread");
+		dev->worker = kthread_run_worker(0, "vpu_irq_thread");
 		if (IS_ERR(dev->worker)) {
 			dev_err(&pdev->dev, "failed to create vpu irq worker\n");
 			ret = PTR_ERR(dev->worker);
diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 284270a4ade1..79311fdf4b5d 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -393,7 +393,7 @@ static int mv88e6xxx_irq_poll_setup(struct mv88e6xxx_chip *chip)
 	kthread_init_delayed_work(&chip->irq_poll_work,
 				  mv88e6xxx_irq_poll);
 
-	chip->kworker = kthread_create_worker(0, "%s", dev_name(chip->dev));
+	chip->kworker = kthread_run_worker(0, "%s", dev_name(chip->dev));
 	if (IS_ERR(chip->kworker))
 		return PTR_ERR(chip->kworker);
 
diff --git a/drivers/net/ethernet/intel/ice/ice_dpll.c b/drivers/net/ethernet/intel/ice/ice_dpll.c
index d5ad6d84007c..75570be61fef 100644
--- a/drivers/net/ethernet/intel/ice/ice_dpll.c
+++ b/drivers/net/ethernet/intel/ice/ice_dpll.c
@@ -2053,7 +2053,7 @@ static int ice_dpll_init_worker(struct ice_pf *pf)
 	struct kthread_worker *kworker;
 
 	kthread_init_delayed_work(&d->work, ice_dpll_periodic_work);
-	kworker = kthread_create_worker(0, "ice-dplls-%s",
+	kworker = kthread_run_worker(0, "ice-dplls-%s",
 					dev_name(ice_pf_to_dev(pf)));
 	if (IS_ERR(kworker))
 		return PTR_ERR(kworker);
diff --git a/drivers/net/ethernet/intel/ice/ice_gnss.c b/drivers/net/ethernet/intel/ice/ice_gnss.c
index c8ea1af51ad3..fcd1f808b696 100644
--- a/drivers/net/ethernet/intel/ice/ice_gnss.c
+++ b/drivers/net/ethernet/intel/ice/ice_gnss.c
@@ -182,7 +182,7 @@ static struct gnss_serial *ice_gnss_struct_init(struct ice_pf *pf)
 	pf->gnss_serial = gnss;
 
 	kthread_init_delayed_work(&gnss->read_work, ice_gnss_read);
-	kworker = kthread_create_worker(0, "ice-gnss-%s", dev_name(dev));
+	kworker = kthread_run_worker(0, "ice-gnss-%s", dev_name(dev));
 	if (IS_ERR(kworker)) {
 		kfree(gnss);
 		return NULL;
diff --git a/drivers/net/ethernet/intel/ice/ice_ptp.c b/drivers/net/ethernet/intel/ice/ice_ptp.c
index ef2e858f49bb..cd7da48bdf91 100644
--- a/drivers/net/ethernet/intel/ice/ice_ptp.c
+++ b/drivers/net/ethernet/intel/ice/ice_ptp.c
@@ -3185,7 +3185,7 @@ static int ice_ptp_init_work(struct ice_pf *pf, struct ice_ptp *ptp)
 	/* Allocate a kworker for handling work required for the ports
 	 * connected to the PTP hardware clock.
 	 */
-	kworker = kthread_create_worker(0, "ice-ptp-%s",
+	kworker = kthread_run_worker(0, "ice-ptp-%s",
 					dev_name(ice_pf_to_dev(pf)));
 	if (IS_ERR(kworker))
 		return PTR_ERR(kworker);
diff --git a/drivers/platform/chrome/cros_ec_spi.c b/drivers/platform/chrome/cros_ec_spi.c
index 86a3d32a7763..08f566cc1480 100644
--- a/drivers/platform/chrome/cros_ec_spi.c
+++ b/drivers/platform/chrome/cros_ec_spi.c
@@ -715,7 +715,7 @@ static int cros_ec_spi_devm_high_pri_alloc(struct device *dev,
 	int err;
 
 	ec_spi->high_pri_worker =
-		kthread_create_worker(0, "cros_ec_spi_high_pri");
+		kthread_run_worker(0, "cros_ec_spi_high_pri");
 
 	if (IS_ERR(ec_spi->high_pri_worker)) {
 		err = PTR_ERR(ec_spi->high_pri_worker);
diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
index c56cd0f63909..89a4420972e7 100644
--- a/drivers/ptp/ptp_clock.c
+++ b/drivers/ptp/ptp_clock.c
@@ -295,7 +295,7 @@ struct ptp_clock *ptp_clock_register(struct ptp_clock_info *info,
 
 	if (ptp->info->do_aux_work) {
 		kthread_init_delayed_work(&ptp->aux_work, ptp_aux_kworker);
-		ptp->kworker = kthread_create_worker(0, "ptp%d", ptp->index);
+		ptp->kworker = kthread_run_worker(0, "ptp%d", ptp->index);
 		if (IS_ERR(ptp->kworker)) {
 			err = PTR_ERR(ptp->kworker);
 			pr_err("failed to create ptp aux_worker %d\n", err);
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index c1dad30a4528..f2f4b6ee25d4 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2053,7 +2053,7 @@ static int spi_init_queue(struct spi_controller *ctlr)
 	ctlr->busy = false;
 	ctlr->queue_empty = true;
 
-	ctlr->kworker = kthread_create_worker(0, dev_name(&ctlr->dev));
+	ctlr->kworker = kthread_run_worker(0, dev_name(&ctlr->dev));
 	if (IS_ERR(ctlr->kworker)) {
 		dev_err(&ctlr->dev, "failed to create message pump kworker\n");
 		return PTR_ERR(ctlr->kworker);
diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
index 7ae341a40342..106756ed0513 100644
--- a/drivers/usb/typec/tcpm/tcpm.c
+++ b/drivers/usb/typec/tcpm/tcpm.c
@@ -7581,7 +7581,7 @@ struct tcpm_port *tcpm_register_port(struct device *dev, struct tcpc_dev *tcpc)
 	mutex_init(&port->lock);
 	mutex_init(&port->swap_lock);
 
-	port->wq = kthread_create_worker(0, dev_name(dev));
+	port->wq = kthread_run_worker(0, dev_name(dev));
 	if (IS_ERR(port->wq))
 		return ERR_CAST(port->wq);
 	sched_set_fifo(port->wq->task);
diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
index 8ffea8430f95..c204fc8e471a 100644
--- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
+++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
@@ -229,7 +229,7 @@ struct vdpasim *vdpasim_create(struct vdpasim_dev_attr *dev_attr,
 	dev = &vdpasim->vdpa.dev;
 
 	kthread_init_work(&vdpasim->work, vdpasim_work_fn);
-	vdpasim->worker = kthread_create_worker(0, "vDPA sim worker: %s",
+	vdpasim->worker = kthread_run_worker(0, "vDPA sim worker: %s",
 						dev_attr->name);
 	if (IS_ERR(vdpasim->worker))
 		goto err_iommu;
diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 4190cb800cc4..19698d87dc57 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -1229,7 +1229,7 @@ int __init watchdog_dev_init(void)
 {
 	int err;
 
-	watchdog_kworker = kthread_create_worker(0, "watchdogd");
+	watchdog_kworker = kthread_run_worker(0, "watchdogd");
 	if (IS_ERR(watchdog_kworker)) {
 		pr_err("Failed to create watchdog kworker\n");
 		return PTR_ERR(watchdog_kworker);
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index e4b5c56a7516..db1f13663cd5 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -318,7 +318,7 @@ static void erofs_destroy_percpu_workers(void)
 static struct kthread_worker *erofs_init_percpu_worker(int cpu)
 {
 	struct kthread_worker *worker =
-		kthread_create_worker_on_cpu(cpu, 0, "erofs_worker/%u");
+		kthread_run_worker_on_cpu(cpu, 0, "erofs_worker/%u");
 
 	if (IS_ERR(worker))
 		return worker;
diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 0c66e7c1092a..8d27403888ce 100644
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -193,19 +193,53 @@ struct kthread_worker *kthread_create_worker_on_node(unsigned int flags,
 						     const char namefmt[], ...);
 
 #define kthread_create_worker(flags, namefmt, ...) \
-({									   \
-	struct kthread_worker *__kw					   \
-		= kthread_create_worker_on_node(flags, NUMA_NO_NODE,	   \
-						namefmt, ## __VA_ARGS__);  \
-	if (!IS_ERR(__kw))						   \
-		wake_up_process(__kw->task);				   \
-	__kw;								   \
+	kthread_create_worker_on_node(flags, NUMA_NO_NODE, namefmt, ## __VA_ARGS__);
+
+/**
+ * kthread_run_worker - create and wake a kthread worker.
+ * @flags: flags modifying the default behavior of the worker
+ * @namefmt: printf-style name for the thread.
+ *
+ * Description: Convenient wrapper for kthread_create_worker() followed by
+ * wake_up_process().  Returns the kthread_worker or ERR_PTR(-ENOMEM).
+ */
+#define kthread_run_worker(flags, namefmt, ...)					\
+({										\
+	struct kthread_worker *__kw						\
+		= kthread_create_worker(flags, namefmt, ## __VA_ARGS__);	\
+	if (!IS_ERR(__kw))							\
+		wake_up_process(__kw->task);					\
+	__kw;									\
 })
 
 struct kthread_worker *
 kthread_create_worker_on_cpu(int cpu, unsigned int flags,
 			     const char namefmt[]);
 
+/**
+ * kthread_run_worker_on_cpu - create and wake a cpu bound kthread worker.
+ * @cpu: CPU number
+ * @flags: flags modifying the default behavior of the worker
+ * @namefmt: printf-style name for the thread. Format is restricted
+ *	     to "name.*%u". Code fills in cpu number.
+ *
+ * Description: Convenient wrapper for kthread_create_worker_on_cpu()
+ * followed by wake_up_process().  Returns the kthread_worker or
+ * ERR_PTR(-ENOMEM).
+ */
+static inline struct kthread_worker *
+kthread_run_worker_on_cpu(int cpu, unsigned int flags,
+			  const char namefmt[])
+{
+	struct kthread_worker *kw;
+
+	kw = kthread_create_worker_on_cpu(cpu, flags, namefmt);
+	if (!IS_ERR(kw))
+		wake_up_process(kw->task);
+
+	return kw;
+}
+
 bool kthread_queue_work(struct kthread_worker *worker,
 			struct kthread_work *work);
 
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 409732fba736..0a1159ffd736 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1077,33 +1077,10 @@ kthread_create_worker_on_node(unsigned int flags, int node, const char namefmt[]
 	worker = __kthread_create_worker_on_node(flags, node, namefmt, args);
 	va_end(args);
 
-	if (worker)
-		wake_up_process(worker->task);
-
 	return worker;
 }
 EXPORT_SYMBOL(kthread_create_worker_on_node);
 
-static __printf(3, 4) struct kthread_worker *
-__kthread_create_worker_on_cpu(int cpu, unsigned int flags,
-			       const char namefmt[], ...)
-{
-	struct kthread_worker *worker;
-	va_list args;
-
-	va_start(args, namefmt);
-	worker = __kthread_create_worker_on_node(flags, cpu_to_node(cpu),
-						 namefmt, args);
-	va_end(args);
-
-	if (worker) {
-		kthread_bind(worker->task, cpu);
-		wake_up_process(worker->task);
-	}
-
-	return worker;
-}
-
 /**
  * kthread_create_worker_on_cpu - create a kthread worker and bind it
  *	to a given CPU and the associated NUMA node.
@@ -1144,7 +1121,13 @@ struct kthread_worker *
 kthread_create_worker_on_cpu(int cpu, unsigned int flags,
 			     const char namefmt[])
 {
-	return __kthread_create_worker_on_cpu(cpu, flags, namefmt, cpu);
+	struct kthread_worker *worker;
+
+	worker = kthread_create_worker_on_node(flags, cpu_to_node(cpu), namefmt, cpu);
+	if (worker)
+		kthread_bind(worker->task, cpu);
+
+	return worker;
 }
 EXPORT_SYMBOL(kthread_create_worker_on_cpu);
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index c9fd28f0f068..65072deb538e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4903,7 +4903,7 @@ static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
 	if (rnp->exp_kworker)
 		return;
 
-	kworker = kthread_create_worker(0, name, rnp_index);
+	kworker = kthread_run_worker(0, name, rnp_index);
 	if (IS_ERR_OR_NULL(kworker)) {
 		pr_err("Failed to create par gp kworker on %d/%d\n",
 		       rnp->grplo, rnp->grphi);
@@ -4930,7 +4930,7 @@ static void __init rcu_start_exp_gp_kworker(void)
 	const char *name = "rcu_exp_gp_kthread_worker";
 	struct sched_param param = { .sched_priority = kthread_prio };
 
-	rcu_exp_gp_kworker = kthread_create_worker(0, name);
+	rcu_exp_gp_kworker = kthread_run_worker(0, name);
 	if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
 		pr_err("Failed to create %s!\n", name);
 		rcu_exp_gp_kworker = NULL;
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index b5f4b1a5ae98..5aef29aaad04 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -4931,7 +4931,7 @@ static struct kthread_worker *scx_create_rt_helper(const char *name)
 {
 	struct kthread_worker *helper;
 
-	helper = kthread_create_worker(0, name);
+	helper = kthread_run_worker(0, name);
 	if (helper)
 		sched_set_fifo(helper->task);
 	return helper;
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9949ffad8df0..f5c7447ae1de 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -7814,7 +7814,7 @@ static void __init wq_cpu_intensive_thresh_init(void)
 	unsigned long thresh;
 	unsigned long bogo;
 
-	pwq_release_worker = kthread_create_worker(0, "pool_workqueue_release");
+	pwq_release_worker = kthread_run_worker(0, "pool_workqueue_release");
 	BUG_ON(IS_ERR(pwq_release_worker));
 
 	/* if the user set it to a specific value, keep it */
diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
index 281bbac5539d..c33d4bf17929 100644
--- a/net/dsa/tag_ksz.c
+++ b/net/dsa/tag_ksz.c
@@ -66,7 +66,7 @@ static int ksz_connect(struct dsa_switch *ds)
 	if (!priv)
 		return -ENOMEM;
 
-	xmit_worker = kthread_create_worker(0, "dsa%d:%d_xmit",
+	xmit_worker = kthread_run_worker(0, "dsa%d:%d_xmit",
 					    ds->dst->index, ds->index);
 	if (IS_ERR(xmit_worker)) {
 		ret = PTR_ERR(xmit_worker);
diff --git a/net/dsa/tag_ocelot_8021q.c b/net/dsa/tag_ocelot_8021q.c
index 8e8b1bef6af6..6ce0bc166792 100644
--- a/net/dsa/tag_ocelot_8021q.c
+++ b/net/dsa/tag_ocelot_8021q.c
@@ -110,7 +110,7 @@ static int ocelot_connect(struct dsa_switch *ds)
 	if (!priv)
 		return -ENOMEM;
 
-	priv->xmit_worker = kthread_create_worker(0, "felix_xmit");
+	priv->xmit_worker = kthread_run_worker(0, "felix_xmit");
 	if (IS_ERR(priv->xmit_worker)) {
 		err = PTR_ERR(priv->xmit_worker);
 		kfree(priv);
diff --git a/net/dsa/tag_sja1105.c b/net/dsa/tag_sja1105.c
index 3e902af7eea6..02adec693811 100644
--- a/net/dsa/tag_sja1105.c
+++ b/net/dsa/tag_sja1105.c
@@ -707,7 +707,7 @@ static int sja1105_connect(struct dsa_switch *ds)
 
 	spin_lock_init(&priv->meta_lock);
 
-	xmit_worker = kthread_create_worker(0, "dsa%d:%d_xmit",
+	xmit_worker = kthread_run_worker(0, "dsa%d:%d_xmit",
 					    ds->dst->index, ds->index);
 	if (IS_ERR(xmit_worker)) {
 		err = PTR_ERR(xmit_worker);
-- 
2.46.0

[PATCH 21/21] rcu: Use kthread preferred affinity for RCU exp kworkers

[Frederic Weisbecker]

Now that kthreads have an infrastructure to handle preferred affinity
against CPU hotplug and housekeeping cpumask, convert RCU exp workers to
use it instead of handling all the constraints by itself.

Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
---
 kernel/rcu/tree.c | 105 +++++++++-------------------------------------
 1 file changed, 19 insertions(+), 86 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 65072deb538e..35949ec1f935 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4891,6 +4891,22 @@ rcu_boot_init_percpu_data(int cpu)
 	rcu_boot_init_nocb_percpu_data(rdp);
 }
 
+static void rcu_thread_affine_rnp(struct task_struct *t, struct rcu_node *rnp)
+{
+	cpumask_var_t affinity;
+	int cpu;
+
+	if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
+		return;
+
+	for_each_leaf_node_possible_cpu(rnp, cpu)
+		cpumask_set_cpu(cpu, affinity);
+
+	kthread_affine_preferred(t, affinity);
+
+	free_cpumask_var(affinity);
+}
+
 struct kthread_worker *rcu_exp_gp_kworker;
 
 static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
@@ -4903,7 +4919,7 @@ static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
 	if (rnp->exp_kworker)
 		return;
 
-	kworker = kthread_run_worker(0, name, rnp_index);
+	kworker = kthread_create_worker(0, name, rnp_index);
 	if (IS_ERR_OR_NULL(kworker)) {
 		pr_err("Failed to create par gp kworker on %d/%d\n",
 		       rnp->grplo, rnp->grphi);
@@ -4913,16 +4929,9 @@ static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
 
 	if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD))
 		sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, &param);
-}
 
-static struct task_struct *rcu_exp_par_gp_task(struct rcu_node *rnp)
-{
-	struct kthread_worker *kworker = READ_ONCE(rnp->exp_kworker);
-
-	if (!kworker)
-		return NULL;
-
-	return kworker->task;
+	rcu_thread_affine_rnp(kworker->task, rnp);
+	wake_up_process(kworker->task);
 }
 
 static void __init rcu_start_exp_gp_kworker(void)
@@ -5007,79 +5016,6 @@ int rcutree_prepare_cpu(unsigned int cpu)
 	return 0;
 }
 
-static void rcu_thread_affine_rnp(struct task_struct *t, struct rcu_node *rnp)
-{
-	cpumask_var_t affinity;
-	int cpu;
-
-	if (!zalloc_cpumask_var(&affinity, GFP_KERNEL))
-		return;
-
-	for_each_leaf_node_possible_cpu(rnp, cpu)
-		cpumask_set_cpu(cpu, affinity);
-
-	kthread_affine_preferred(t, affinity);
-
-	free_cpumask_var(affinity);
-}
-
-/*
- * Update kthreads affinity during CPU-hotplug changes.
- *
- * Set the per-rcu_node kthread's affinity to cover all CPUs that are
- * served by the rcu_node in question.  The CPU hotplug lock is still
- * held, so the value of rnp->qsmaskinit will be stable.
- *
- * We don't include outgoingcpu in the affinity set, use -1 if there is
- * no outgoing CPU.  If there are no CPUs left in the affinity set,
- * this function allows the kthread to execute on any CPU.
- *
- * Any future concurrent calls are serialized via ->kthread_mutex.
- */
-static void rcutree_affinity_setting(unsigned int cpu, int outgoingcpu)
-{
-	cpumask_var_t cm;
-	unsigned long mask;
-	struct rcu_data *rdp;
-	struct rcu_node *rnp;
-	struct task_struct *task_exp;
-
-	rdp = per_cpu_ptr(&rcu_data, cpu);
-	rnp = rdp->mynode;
-
-	task_exp = rcu_exp_par_gp_task(rnp);
-
-	/*
-	 * If CPU is the boot one, this task is created later from early
-	 * initcall since kthreadd must be created first.
-	 */
-	if (!task_exp)
-		return;
-
-	if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
-		return;
-
-	mutex_lock(&rnp->kthread_mutex);
-	mask = rcu_rnp_online_cpus(rnp);
-	for_each_leaf_node_possible_cpu(rnp, cpu)
-		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
-		    cpu != outgoingcpu)
-			cpumask_set_cpu(cpu, cm);
-	cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
-	if (cpumask_empty(cm)) {
-		cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
-		if (outgoingcpu >= 0)
-			cpumask_clear_cpu(outgoingcpu, cm);
-	}
-
-	if (task_exp)
-		set_cpus_allowed_ptr(task_exp, cm);
-
-	mutex_unlock(&rnp->kthread_mutex);
-
-	free_cpumask_var(cm);
-}
-
 /*
  * Has the specified (known valid) CPU ever been fully online?
  */
@@ -5108,7 +5044,6 @@ int rcutree_online_cpu(unsigned int cpu)
 	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
 		return 0; /* Too early in boot for scheduler work. */
 	sync_sched_exp_online_cleanup(cpu);
-	rcutree_affinity_setting(cpu, -1);
 
 	// Stop-machine done, so allow nohz_full to disable tick.
 	tick_dep_clear(TICK_DEP_BIT_RCU);
@@ -5325,8 +5260,6 @@ int rcutree_offline_cpu(unsigned int cpu)
 	rnp->ffmask &= ~rdp->grpmask;
 	raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 
-	rcutree_affinity_setting(cpu, cpu);
-
 	// nohz_full CPUs need the tick for stop-machine to work quickly
 	tick_dep_set(TICK_DEP_BIT_RCU);
 	return 0;
-- 
2.46.0

Re: [PATCH 02/21] x86/resctrl: Use kthread_run_on_cpu()

[Fenghua Yu]

On 11/12/24 06:22, Frederic Weisbecker wrote:
> Use the proper API instead of open coding it.
> 
> Acked-by: Reinette Chatre <reinette.chatre@intel.com>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Acked-by: Fenghua Yu <fenghua.yu@intel.com>

> ---
>   arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 28 +++++++----------------
>   1 file changed, 8 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> index 972e6b6b0481..6c60c16a9dd0 100644
> --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> @@ -1205,20 +1205,14 @@ static int pseudo_lock_measure_cycles(struct rdtgroup *rdtgrp, int sel)
>   	plr->cpu = cpu;
>   
>   	if (sel == 1)
> -		thread = kthread_create_on_node(measure_cycles_lat_fn, plr,
> -						cpu_to_node(cpu),
> -						"pseudo_lock_measure/%u",
> -						cpu);
> +		thread = kthread_run_on_cpu(measure_cycles_lat_fn, plr,
> +					    cpu, "pseudo_lock_measure/%u");
>   	else if (sel == 2)
> -		thread = kthread_create_on_node(measure_l2_residency, plr,
> -						cpu_to_node(cpu),
> -						"pseudo_lock_measure/%u",
> -						cpu);
> +		thread = kthread_run_on_cpu(measure_l2_residency, plr,
> +					    cpu, "pseudo_lock_measure/%u");
>   	else if (sel == 3)
> -		thread = kthread_create_on_node(measure_l3_residency, plr,
> -						cpu_to_node(cpu),
> -						"pseudo_lock_measure/%u",
> -						cpu);
> +		thread = kthread_run_on_cpu(measure_l3_residency, plr,
> +					    cpu, "pseudo_lock_measure/%u");
>   	else
>   		goto out;
>   
> @@ -1226,8 +1220,6 @@ static int pseudo_lock_measure_cycles(struct rdtgroup *rdtgrp, int sel)
>   		ret = PTR_ERR(thread);
>   		goto out;
>   	}
> -	kthread_bind(thread, cpu);
> -	wake_up_process(thread);
>   
>   	ret = wait_event_interruptible(plr->lock_thread_wq,
>   				       plr->thread_done == 1);
> @@ -1315,18 +1307,14 @@ int rdtgroup_pseudo_lock_create(struct rdtgroup *rdtgrp)
>   
>   	plr->thread_done = 0;
>   
> -	thread = kthread_create_on_node(pseudo_lock_fn, rdtgrp,
> -					cpu_to_node(plr->cpu),
> -					"pseudo_lock/%u", plr->cpu);
> +	thread = kthread_run_on_cpu(pseudo_lock_fn, rdtgrp,
> +				    plr->cpu, "pseudo_lock/%u");
>   	if (IS_ERR(thread)) {
>   		ret = PTR_ERR(thread);
>   		rdt_last_cmd_printf("Locking thread returned error %d\n", ret);
>   		goto out_cstates;
>   	}
>   
> -	kthread_bind(thread, plr->cpu);
> -	wake_up_process(thread);
> -
>   	ret = wait_event_interruptible(plr->lock_thread_wq,
>   				       plr->thread_done == 1);
>   	if (ret < 0) {

Thanks.

-Fenghua

Re: [PATCH 11/21] arm64: Keep first mismatched 32bits el0 capable CPU online through its callbacks

[Will Deacon]

Hi Frederic,

On Tue, Nov 12, 2024 at 03:22:35PM +0100, Frederic Weisbecker wrote:
> The first mismatched 32bits el0 capable CPU is designated as the last
> resort CPU for compat 32 bits tasks. As such this CPU is forbidden to
> go offline.
> 
> However this restriction is applied to the device object of the CPU,
> which is not easy to revert later if needed because other components may
> have forbidden the target to be offline and they are not tracked.
> 
> But the task cpu possible mask is going to be made aware of housekeeping
> CPUs. In that context, a better 32 bits el0 last resort CPU may be found
> later on boot. When that happens, the old fallback can be made
> offlineable again.
> 
> To make this possible and more flexible, drive the offlineable decision
> from the cpuhotplug callbacks themselves.

Sadly, I don't think this can work.

> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index 718728a85430..53ee8ce38d5b 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -3591,15 +3591,15 @@ void __init setup_user_features(void)
>  	minsigstksz_setup();
>  }
>  
> -static int enable_mismatched_32bit_el0(unsigned int cpu)
> -{
> -	/*
> -	 * The first 32-bit-capable CPU we detected and so can no longer
> -	 * be offlined by userspace. -1 indicates we haven't yet onlined
> -	 * a 32-bit-capable CPU.
> -	 */
> -	static int lucky_winner = -1;
> +/*
> + * The first 32-bit-capable CPU we detected and so can no longer
> + * be offlined by userspace. -1 indicates we haven't yet onlined
> + * a 32-bit-capable CPU.
> + */
> +static int cpu_32bit_unofflineable = -1;
>  
> +static int mismatched_32bit_el0_online(unsigned int cpu)
> +{
>  	struct cpuinfo_arm64 *info = &per_cpu(cpu_data, cpu);
>  	bool cpu_32bit = id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0);
>  
> @@ -3611,7 +3611,7 @@ static int enable_mismatched_32bit_el0(unsigned int cpu)
>  	if (cpumask_test_cpu(0, cpu_32bit_el0_mask) == cpu_32bit)
>  		return 0;
>  
> -	if (lucky_winner >= 0)
> +	if (cpu_32bit_unofflineable < 0)

nit: I think you meant '>=' here, but it doesn't matter. See below..

> +static int mismatched_32bit_el0_offline(unsigned int cpu)
> +{
> +	return cpu == cpu_32bit_unofflineable ? -EBUSY : 0;
> +}

I think this is far too late. The reason we prevent hot-unplug of the
last 32-bit CPU is because 32-bit tasks need somewhere to run. By the
time our offline notifier runs, those tasks have already been migrated.

On my setup, this explodes because that migration fails (as expected):


[  125.954586] ------------[ cut here ]------------
[  125.955661] kernel BUG at kernel/sched/core.c:3501!
[  125.957585] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
[  125.959371] Modules linked in:
[  125.961850] CPU: 2 UID: 0 PID: 27 Comm: migration/2 Not tainted 6.12.0-00001-ge7689036c862-dirty #10
[  125.963711] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
[  125.964859] Stopper: __balance_push_cpu_stop+0x0/0x134 <- balance_push+0x118/0x1ac
[  125.968507] pstate: 614000c9 (nZCv daIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[  125.969648] pc : select_fallback_rq+0x2f4/0x2f8
[  125.970477] lr : select_fallback_rq+0x198/0x2f8
[  125.971273] sp : ffff800080153d20
[  125.971897] x29: ffff800080153d30 x28: 0000000000000002 x27: ffffddbd31d79d30
[  125.973416] x26: 0000000000000001 x25: ffffddbd31d79c70 x24: 0000000000000008
[  125.974436] x23: ffffddbd31d79000 x22: ffffddbd31a77190 x21: 0000000000000004
[  125.975452] x20: ffff0000c506a280 x19: 0000000000000000 x18: ffffddbd30fb1df0
[  125.976467] x17: 0000000000000000 x16: 0000000000000001 x15: 000000000018132d
[  125.977490] x14: 00000000ffffffe0 x13: 0000040000000000 x12: 00000c0000000000
[  125.978499] x11: 000000002ae00002 x10: 000000000000000c x9 : 0000000000000040
[  125.979507] x8 : 0000000000000000 x7 : 000000000000000c x6 : 000000000000000c
[  125.980501] x5 : ffff0000c506a578 x4 : ffffddbd2fe53eb0 x3 : 0000000000000010
[  125.981508] x2 : 0000000000000004 x1 : 0000000000000004 x0 : 0000000000000004
[  125.982671] Call trace:
[  125.983065]  select_fallback_rq+0x2f4/0x2f8
[  125.983550]  __balance_push_cpu_stop+0x94/0x134
[  125.983983]  cpu_stopper_thread+0xbc/0x174
[  125.984352]  smpboot_thread_fn+0x1e4/0x24c
[  125.984732]  kthread+0xfc/0x184
[  125.985065]  ret_from_fork+0x10/0x20
[  125.985741] Code: 9000d9c0 91306000 9441667a 17ffffef (d4210000) 
[  125.986445] ---[ end trace 0000000000000000 ]---


As I mentioned before, I think we need to turn this the other way around
so that the non-unpluggable 32-bit core is forced to be a housekeeping]
CPU. You said it was hard to revert CPUs from being treated as nohz_full,
but I'm wondering whether we can prevent it from being added in the first
place. The arch code has fingers in all the early boot pies.

Yet another option (which I'm not hugely fond of, but may be ok) would
be to treat 32-bit-capable nohz_full CPUs as being 64-bit-only when
'allow_mismatched_32bit_el0' is enabled (and documenting this as a
limitation).

Will

Re: [PATCH 11/21] arm64: Keep first mismatched 32bits el0 capable CPU online through its callbacks

[Frederic Weisbecker]

Le Thu, Nov 28, 2024 at 04:26:19PM +0000, Will Deacon a écrit :
> Hi Frederic,
> 
> On Tue, Nov 12, 2024 at 03:22:35PM +0100, Frederic Weisbecker wrote:
> > +static int mismatched_32bit_el0_offline(unsigned int cpu)
> > +{
> > +	return cpu == cpu_32bit_unofflineable ? -EBUSY : 0;
> > +}
> 
> I think this is far too late. The reason we prevent hot-unplug of the
> last 32-bit CPU is because 32-bit tasks need somewhere to run. By the
> time our offline notifier runs, those tasks have already been migrated.
> 
> On my setup, this explodes because that migration fails (as expected):

Duh!

> 
> 
> [  125.954586] ------------[ cut here ]------------
> [  125.955661] kernel BUG at kernel/sched/core.c:3501!
> [  125.957585] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
> [  125.959371] Modules linked in:
> [  125.961850] CPU: 2 UID: 0 PID: 27 Comm: migration/2 Not tainted 6.12.0-00001-ge7689036c862-dirty #10
> [  125.963711] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
> [  125.964859] Stopper: __balance_push_cpu_stop+0x0/0x134 <- balance_push+0x118/0x1ac
> [  125.968507] pstate: 614000c9 (nZCv daIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> [  125.969648] pc : select_fallback_rq+0x2f4/0x2f8
> [  125.970477] lr : select_fallback_rq+0x198/0x2f8
> [  125.971273] sp : ffff800080153d20
> [  125.971897] x29: ffff800080153d30 x28: 0000000000000002 x27: ffffddbd31d79d30
> [  125.973416] x26: 0000000000000001 x25: ffffddbd31d79c70 x24: 0000000000000008
> [  125.974436] x23: ffffddbd31d79000 x22: ffffddbd31a77190 x21: 0000000000000004
> [  125.975452] x20: ffff0000c506a280 x19: 0000000000000000 x18: ffffddbd30fb1df0
> [  125.976467] x17: 0000000000000000 x16: 0000000000000001 x15: 000000000018132d
> [  125.977490] x14: 00000000ffffffe0 x13: 0000040000000000 x12: 00000c0000000000
> [  125.978499] x11: 000000002ae00002 x10: 000000000000000c x9 : 0000000000000040
> [  125.979507] x8 : 0000000000000000 x7 : 000000000000000c x6 : 000000000000000c
> [  125.980501] x5 : ffff0000c506a578 x4 : ffffddbd2fe53eb0 x3 : 0000000000000010
> [  125.981508] x2 : 0000000000000004 x1 : 0000000000000004 x0 : 0000000000000004
> [  125.982671] Call trace:
> [  125.983065]  select_fallback_rq+0x2f4/0x2f8
> [  125.983550]  __balance_push_cpu_stop+0x94/0x134
> [  125.983983]  cpu_stopper_thread+0xbc/0x174
> [  125.984352]  smpboot_thread_fn+0x1e4/0x24c
> [  125.984732]  kthread+0xfc/0x184
> [  125.985065]  ret_from_fork+0x10/0x20
> [  125.985741] Code: 9000d9c0 91306000 9441667a 17ffffef (d4210000) 
> [  125.986445] ---[ end trace 0000000000000000 ]---
> 
> 
> As I mentioned before, I think we need to turn this the other way around
> so that the non-unpluggable 32-bit core is forced to be a housekeeping]
> CPU. You said it was hard to revert CPUs from being treated as nohz_full,
> but I'm wondering whether we can prevent it from being added in the first
> place. The arch code has fingers in all the early boot pies.

So the mismatch is detected (and the unpluggableability forced) late on boot,
during secondary boot up. OTOH housekeeping is set up much earlier, on kernel
parameters parsing. Would it be possible to detect at this stage if a
possible yet non-booted CPU doesn't support 32bits el0?


> Yet another option (which I'm not hugely fond of, but may be ok) would
> be to treat 32-bit-capable nohz_full CPUs as being 64-bit-only when
> 'allow_mismatched_32bit_el0' is enabled (and documenting this as a
> limitation).

There is that too indeed.

Thanks.

> 
> Will

Re: [PATCH 11/21] arm64: Keep first mismatched 32bits el0 capable CPU online through its callbacks

[Will Deacon]

On Fri, Nov 29, 2024 at 11:15:48PM +0100, Frederic Weisbecker wrote:
> Le Thu, Nov 28, 2024 at 04:26:19PM +0000, Will Deacon a écrit :
> > Hi Frederic,
> > 
> > On Tue, Nov 12, 2024 at 03:22:35PM +0100, Frederic Weisbecker wrote:
> > > +static int mismatched_32bit_el0_offline(unsigned int cpu)
> > > +{
> > > +	return cpu == cpu_32bit_unofflineable ? -EBUSY : 0;
> > > +}
> > 
> > I think this is far too late. The reason we prevent hot-unplug of the
> > last 32-bit CPU is because 32-bit tasks need somewhere to run. By the
> > time our offline notifier runs, those tasks have already been migrated.
> > 
> > On my setup, this explodes because that migration fails (as expected):
> 
> Duh!
> 
> > 
> > 
> > [  125.954586] ------------[ cut here ]------------
> > [  125.955661] kernel BUG at kernel/sched/core.c:3501!
> > [  125.957585] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
> > [  125.959371] Modules linked in:
> > [  125.961850] CPU: 2 UID: 0 PID: 27 Comm: migration/2 Not tainted 6.12.0-00001-ge7689036c862-dirty #10
> > [  125.963711] Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015
> > [  125.964859] Stopper: __balance_push_cpu_stop+0x0/0x134 <- balance_push+0x118/0x1ac
> > [  125.968507] pstate: 614000c9 (nZCv daIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
> > [  125.969648] pc : select_fallback_rq+0x2f4/0x2f8
> > [  125.970477] lr : select_fallback_rq+0x198/0x2f8
> > [  125.971273] sp : ffff800080153d20
> > [  125.971897] x29: ffff800080153d30 x28: 0000000000000002 x27: ffffddbd31d79d30
> > [  125.973416] x26: 0000000000000001 x25: ffffddbd31d79c70 x24: 0000000000000008
> > [  125.974436] x23: ffffddbd31d79000 x22: ffffddbd31a77190 x21: 0000000000000004
> > [  125.975452] x20: ffff0000c506a280 x19: 0000000000000000 x18: ffffddbd30fb1df0
> > [  125.976467] x17: 0000000000000000 x16: 0000000000000001 x15: 000000000018132d
> > [  125.977490] x14: 00000000ffffffe0 x13: 0000040000000000 x12: 00000c0000000000
> > [  125.978499] x11: 000000002ae00002 x10: 000000000000000c x9 : 0000000000000040
> > [  125.979507] x8 : 0000000000000000 x7 : 000000000000000c x6 : 000000000000000c
> > [  125.980501] x5 : ffff0000c506a578 x4 : ffffddbd2fe53eb0 x3 : 0000000000000010
> > [  125.981508] x2 : 0000000000000004 x1 : 0000000000000004 x0 : 0000000000000004
> > [  125.982671] Call trace:
> > [  125.983065]  select_fallback_rq+0x2f4/0x2f8
> > [  125.983550]  __balance_push_cpu_stop+0x94/0x134
> > [  125.983983]  cpu_stopper_thread+0xbc/0x174
> > [  125.984352]  smpboot_thread_fn+0x1e4/0x24c
> > [  125.984732]  kthread+0xfc/0x184
> > [  125.985065]  ret_from_fork+0x10/0x20
> > [  125.985741] Code: 9000d9c0 91306000 9441667a 17ffffef (d4210000) 
> > [  125.986445] ---[ end trace 0000000000000000 ]---
> > 
> > 
> > As I mentioned before, I think we need to turn this the other way around
> > so that the non-unpluggable 32-bit core is forced to be a housekeeping]
> > CPU. You said it was hard to revert CPUs from being treated as nohz_full,
> > but I'm wondering whether we can prevent it from being added in the first
> > place. The arch code has fingers in all the early boot pies.
> 
> So the mismatch is detected (and the unpluggableability forced) late on boot,
> during secondary boot up. OTOH housekeeping is set up much earlier, on kernel
> parameters parsing. Would it be possible to detect at this stage if a
> possible yet non-booted CPU doesn't support 32bits el0?

Sadly not; we need the CPU to enter the kernel so that we can inspect its
ID registers. We _do_ do this before the CPU is marked as online, but we
can't tell before it's actually up and running.

> > Yet another option (which I'm not hugely fond of, but may be ok) would
> > be to treat 32-bit-capable nohz_full CPUs as being 64-bit-only when
> > 'allow_mismatched_32bit_el0' is enabled (and documenting this as a
> > limitation).
> 
> There is that too indeed.

Maybe that's what we do then (but *please* update 'asymmetric-32bit.rst').

Will