Re: RCU stall

[Bart Van Assche <bart.vanassche@sandisk.com>]

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On 03/22/2016 07:29 PM, Paul E. McKenney wrote:
> Note that a soft lockup triggered at 10509.568010, well before the RCU
> CPU stall warning..  And you have a second soft lockup at 10537.567212,
> with the same funtion scsi_request_fn() at the top of the stack in both
> stack traces.  That function has a nice big "for (;;)" loop that does
> not appear to have any iteration-limiting mechanism.

Hello Paul,

Your feedback is really appreciated. I have started with testing the 
four attached patches. With the tests I ran so far these patches were 
sufficient to avoid any soft lockup or RCU stall complaints. I will 
submit these patches to the appropriate maintainers once I have finished 
testing these patches.

Bart.

[-- Attachment #2: 0001-IB-cm-Fix-a-recently-introduced-locking-bug.patch --]
[-- Type: text/x-patch, Size: 3020 bytes --]

>From 0f72b28329342346980ae99c69d19b7adb0123bc Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bart.vanassche@sandisk.com>
Date: Thu, 24 Mar 2016 11:01:14 -0700
Subject: [PATCH 1/4] IB/cm: Fix a recently introduced locking bug

ib_cm_notify() can be called from interrupt context. Hence do not
reenable interrupts unconditionally in cm_establish().

This patch avoids that lockdep reports the following warning:

WARNING: CPU: 0 PID: 23317 at kernel/locking/lockdep.c:2624 trace _hardirqs_on_caller+0x112/0x1b0
DEBUG_LOCKS_WARN_ON(current->hardirq_context)
Call Trace:
 <IRQ>  [<ffffffff812bd0e5>] dump_stack+0x67/0x92
 [<ffffffff81056f21>] __warn+0xc1/0xe0
 [<ffffffff81056f8a>] warn_slowpath_fmt+0x4a/0x50
 [<ffffffff810a5932>] trace_hardirqs_on_caller+0x112/0x1b0
 [<ffffffff810a59dd>] trace_hardirqs_on+0xd/0x10
 [<ffffffff815992c7>] _raw_spin_unlock_irq+0x27/0x40
 [<ffffffffa0382e9c>] ib_cm_notify+0x25c/0x290 [ib_cm]
 [<ffffffffa068fbc1>] srpt_qp_event+0xa1/0xf0 [ib_srpt]
 [<ffffffffa04efb97>] mlx4_ib_qp_event+0x67/0xd0 [mlx4_ib]
 [<ffffffffa034ec0a>] mlx4_qp_event+0x5a/0xc0 [mlx4_core]
 [<ffffffffa03365f8>] mlx4_eq_int+0x3d8/0xcf0 [mlx4_core]
 [<ffffffffa0336f9c>] mlx4_msi_x_interrupt+0xc/0x20 [mlx4_core]
 [<ffffffff810b0914>] handle_irq_event_percpu+0x64/0x100
 [<ffffffff810b09e4>] handle_irq_event+0x34/0x60
 [<ffffffff810b3a6a>] handle_edge_irq+0x6a/0x150
 [<ffffffff8101ad05>] handle_irq+0x15/0x20
 [<ffffffff8101a66c>] do_IRQ+0x5c/0x110
 [<ffffffff8159a2c9>] common_interrupt+0x89/0x89
 [<ffffffff81297a17>] blk_run_queue_async+0x37/0x40
 [<ffffffffa0163e53>] rq_completed+0x43/0x70 [dm_mod]
 [<ffffffffa0164896>] dm_softirq_done+0x176/0x280 [dm_mod]
 [<ffffffff812a26c2>] blk_done_softirq+0x52/0x90
 [<ffffffff8105bc1f>] __do_softirq+0x10f/0x230
 [<ffffffff8105bec8>] irq_exit+0xa8/0xb0
 [<ffffffff8103653e>] smp_trace_call_function_single_interrupt+0x2e/0x30
 [<ffffffff81036549>] smp_call_function_single_interrupt+0x9/0x10
 [<ffffffff8159a959>] call_function_single_interrupt+0x89/0x90
 <EOI>

Fixes: commit be4b499323bf ("IB/cm: Do not queue work to a device that's going away")
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Erez Shitrit <erezsh@mellanox.com>
Cc: Doug Ledford <dledford@redhat.com>
Cc: stable <stable@vger.kernel.org> # v4.2+
---
 drivers/infiniband/core/cm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index 1d92e09..c995255 100644
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -3452,14 +3452,14 @@ static int cm_establish(struct ib_cm_id *cm_id)
 	work->cm_event.event = IB_CM_USER_ESTABLISHED;
 
 	/* Check if the device started its remove_one */
-	spin_lock_irq(&cm.lock);
+	spin_lock_irqsave(&cm.lock, flags);
 	if (!cm_dev->going_down) {
 		queue_delayed_work(cm.wq, &work->work, 0);
 	} else {
 		kfree(work);
 		ret = -ENODEV;
 	}
-	spin_unlock_irq(&cm.lock);
+	spin_unlock_irqrestore(&cm.lock, flags);
 
 out:
 	return ret;
-- 
2.7.3


[-- Attachment #3: 0002-kernel-kthread.c-Avoid-CPU-lockups.patch --]
[-- Type: text/x-patch, Size: 1765 bytes --]

>From 5fd6aedadc04d102cd261507ff61071071455fb6 Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bart.vanassche@sandisk.com>
Date: Thu, 24 Mar 2016 12:04:01 -0700
Subject: [PATCH 2/4] kernel/kthread.c: Avoid CPU lockups

Avoid that complaints similar to the one below are reported against
a debug kernel:

NMI watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [kdmwork-25 4:2:23313]
irq event stamp: 16320042
hardirqs last  enabled at (16320041): [<ffffffff815992c7>] _raw_spin_unlock_irq+0x27/0x40
hardirqs last disabled at (16320042): [<ffff8803ffbe3cd8>] 0xffff8803ffbe3cd8
softirqs last  enabled at (16319960): [<ffffffff8105bcdb>] __do_softirq+0x1cb/0x230
softirqs last disabled at (16319715): [<ffffffff8105bec8>] irq_exit+0xa8/0xb0
CPU: 1 PID: 23313 Comm: kdmwork-254:2
RIP: 0010:[<ffffffff815992cf>]  [<ffffffff815992cf>] _raw_spin_unlock_irq+0x2f/0x40
Call Trace:
 [<ffffffff813f702f>] scsi_request_fn+0x11f/0x630
 [<ffffffff812977fe>] __blk_run_queue+0x2e/0x40
 [<ffffffff81297065>] __elv_add_request+0x75/0x1f0
 [<ffffffff8129ba91>] blk_insert_cloned_request+0x101/0x190
 [<ffffffffa0189f1a>] map_request+0x16a/0x1b0 [dm_mod]
 [<ffffffffa0189f7d>] map_tio_request+0x1d/0x40 [dm_mod]
 [<ffffffff81077812>] kthread_worker_fn+0x82/0x1a0
 [<ffffffff8107771a>] kthread+0xea/0x100
 [<ffffffff81599b72>] ret_from_fork+0x22/0x40

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
---
 kernel/kthread.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 9ff173d..516ca6b 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -593,6 +593,7 @@ repeat:
 	if (work) {
 		__set_current_state(TASK_RUNNING);
 		work->func(work);
+		cond_resched_rcu_qs();
 	} else if (!freezing(current))
 		schedule();
 
-- 
2.7.3


[-- Attachment #4: 0003-block-Limit-work-processed-in-softirq-context.patch --]
[-- Type: text/x-patch, Size: 2854 bytes --]

>From 44985e4b2f3124bf87e84a4c7572efa00ac28d3b Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bart.vanassche@sandisk.com>
Date: Wed, 23 Mar 2016 17:14:57 -0700
Subject: [PATCH 3/4] block: Limit work processed in softirq context

Avoid that complaints like the one below are reported against a
debug kernel:

NMI watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [disk11_0:2708]
irq event stamp: 17120809
hardirqs last  enabled at (17120808): [<ffffffff81599191>] _raw_spin_unlock_irqrestore+0x31/0x50
hardirqs last disabled at (17120809): [<ffff88046f223bd0>] 0xffff88046f223bd0
softirqs last  enabled at (17120794): [<ffffffffa060aa67>] scst_check_blocked_dev+0x77/0x1c0 [scst]
softirqs last disabled at (17120795): [<ffffffff8159acbc>] do_softirq_own_stack+0x1c/0x30
RIP: 0010:[<ffffffff81599193>]  [<ffffffff81599193>] _raw_spin_unlock_irqrestore+0x33/0x50
Call Trace:
 <IRQ>
 [<ffffffff81171450>] free_debug_processing+0x270/0x3a0
 [<ffffffff8117277a>] __slab_free+0x17a/0x2c0
 [<ffffffff81172a74>] kmem_cache_free+0x1b4/0x1d0
 [<ffffffff8111a6c2>] mempool_free_slab+0x12/0x20
 [<ffffffff8111a846>] mempool_free+0x26/0x80
 [<ffffffff81294cb9>] bio_free+0x49/0x60
 [<ffffffff81294cee>] bio_put+0x1e/0x30
 [<ffffffffa0199d31>] end_clone_bio+0x21/0x70 [dm_mod]
 [<ffffffff81294d52>] bio_endio+0x52/0x60
 [<ffffffff8129aaec>] blk_update_request+0x7c/0x2a0
 [<ffffffff813f4a8e>] scsi_end_request+0x2e/0x1d0
 [<ffffffff813f7674>] scsi_io_completion+0xb4/0x610
 [<ffffffff813ee79a>] scsi_finish_command+0xca/0x120
 [<ffffffff813f6ef0>] scsi_softirq_done+0x120/0x140
 [<ffffffff812a26e6>] blk_done_softirq+0x76/0x90
 [<ffffffff8105bc1f>] __do_softirq+0x10f/0x230
 [<ffffffff8159acbc>] do_softirq_own_stack+0x1c/0x30
 <EOI>
---
 block/blk-softirq.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index 53b1737..d739949 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -20,20 +20,26 @@ static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
  */
 static void blk_done_softirq(struct softirq_action *h)
 {
-	struct list_head *cpu_list, local_list;
+	struct list_head *cpu_list = this_cpu_ptr(&blk_cpu_done);
+	struct request *rq;
+	int i;
 
 	local_irq_disable();
-	cpu_list = this_cpu_ptr(&blk_cpu_done);
-	list_replace_init(cpu_list, &local_list);
-	local_irq_enable();
-
-	while (!list_empty(&local_list)) {
-		struct request *rq;
-
-		rq = list_entry(local_list.next, struct request, ipi_list);
+	for (i = 64; i > 0; i--) {
+		if (list_empty(cpu_list))
+			goto done;
+		rq = list_first_entry(cpu_list, struct request, ipi_list);
 		list_del_init(&rq->ipi_list);
+		local_irq_enable();
+
 		rq->q->softirq_done_fn(rq);
+
+		local_irq_disable();
 	}
+	raise_softirq_irqoff(BLOCK_SOFTIRQ);
+
+done:
+	local_irq_enable();
 }
 
 #ifdef CONFIG_SMP
-- 
2.7.3


[-- Attachment #5: 0004-Avoid-that-I-O-completion-processing-triggers-lockup.patch --]
[-- Type: text/x-patch, Size: 4862 bytes --]

>From a73fdf710b98922fa02d464af96b499ea2740832 Mon Sep 17 00:00:00 2001
From: Bart Van Assche <bart.vanassche@sandisk.com>
Date: Wed, 23 Mar 2016 14:38:13 -0700
Subject: [PATCH 4/4] Avoid that I/O completion processing triggers lockup
 complaints

Avoid that I/O completion processing triggers the following complaints
if kernel debug options that slow down the kernel significantly are
enabled:

NMI watchdog: BUG: soft lockup - CPU#3 stuck for 22s! [kdmwork-254:2:358]
irq event stamp: 15233868
hardirqs last  enabled at (15233867): [<ffffffff81578167>] _raw_spin_unlock_irq+0x27/0x40
hardirqs last disabled at (15233868): [<ffffffff81579664>] apic_timer_interrupt+0x84/0x90
softirqs last  enabled at (15233850): [<ffffffff8105a55b>] __do_softirq+0x1cb/0x230
softirqs last disabled at (15233743): [<ffffffff8105a748>] irq_exit+0xa8/0xb0
CPU: 3 PID: 358 Comm: kdmwork-254:2
RIP: 0010:[<ffffffff8157816f>]  [<ffffffff8157816f>] _raw_spin_unlock_irq+0x2f/0x40
Call Trace:
 [<ffffffff813dbe28>] scsi_request_fn+0x118/0x600
 [<ffffffff8128190e>] __blk_run_queue+0x2e/0x40
 [<ffffffff81281175>] __elv_add_request+0x75/0x1f0
 [<ffffffff81285b11>] blk_insert_cloned_request+0x101/0x190
 [<ffffffffa0170eee>] map_request+0x18e/0x210 [dm_mod]
 [<ffffffffa0170f8d>] map_tio_request+0x1d/0x40 [dm_mod]
 [<ffffffff81075a0d>] kthread_worker_fn+0x7d/0x1a0
 [<ffffffff8107591a>] kthread+0xea/0x100
 [<ffffffff81578c7f>] ret_from_fork+0x3f/0x70

INFO: rcu_sched self-detected stall on CPU
 3-...: (6497 ticks this GP) idle=fb9/140000000000002/0 softirq=2044956/2045037 fqs=5414
  (t=6500 jiffies g=219289 c=219288 q=7233211)
Task dump for CPU 3:
kdmwork-254:2   R  running task        0   358      2 0x00000008
Call Trace:
 <IRQ>  [<ffffffff8108195f>] sched_show_task+0xbf/0x150
 [<ffffffff81084742>] dump_cpu_task+0x32/0x40
 [<ffffffff810b5e79>] rcu_dump_cpu_stacks+0x89/0xe0
 [<ffffffff810b9999>] rcu_check_callbacks+0x439/0x730
 [<ffffffff810bc1c4>] update_process_times+0x34/0x60
 [<ffffffff810caaa0>] tick_sched_handle.isra.18+0x20/0x50
 [<ffffffff810cb148>] tick_sched_timer+0x38/0x70
 [<ffffffff810bc865>] __hrtimer_run_queues+0xa5/0x1c0
 [<ffffffff810bcef6>] hrtimer_interrupt+0xa6/0x1b0
 [<ffffffff81038ba3>] smp_trace_apic_timer_interrupt+0x63/0x90
 [<ffffffff81038bd9>] smp_apic_timer_interrupt+0x9/0x10
 [<ffffffff81579669>] apic_timer_interrupt+0x89/0x90
 [<ffffffff811640d6>] __slab_free+0xc6/0x270
 [<ffffffff811643d9>] kmem_cache_free+0x159/0x160
 [<ffffffff811d0a12>] kiocb_free+0x32/0x40
 [<ffffffff811d1b75>] aio_complete+0x1e5/0x3c0
 [<ffffffff811bef45>] dio_complete+0x75/0x1d0
 [<ffffffff811bf11a>] dio_bio_end_aio+0x7a/0x130
 [<ffffffff812800da>] bio_endio+0x3a/0x60
 [<ffffffff81284b7c>] blk_update_request+0x7c/0x2a0
 [<ffffffffa016fcc1>] end_clone_bio+0x41/0x70 [dm_mod]
 [<ffffffff812800da>] bio_endio+0x3a/0x60
 [<ffffffff81284b7c>] blk_update_request+0x7c/0x2a0
 [<ffffffff813da01e>] scsi_end_request+0x2e/0x1d0
 [<ffffffff813dc444>] scsi_io_completion+0xb4/0x610
 [<ffffffff813d3e0a>] scsi_finish_command+0xca/0x120
 [<ffffffff813dbcf0>] scsi_softirq_done+0x120/0x140
 [<ffffffff8128c742>] blk_done_softirq+0x72/0x90
 [<ffffffff8105a49f>] __do_softirq+0x10f/0x230
 [<ffffffff8105a748>] irq_exit+0xa8/0xb0
 [<ffffffff810065a5>] do_IRQ+0x65/0x110
 [<ffffffff815793c9>] common_interrupt+0x89/0x89
 <EOI>
 [<ffffffffa010f815>] __multipath_map.isra.16+0x145/0x260 [dm_multipath]
 [<ffffffffa010f962>] multipath_map+0x12/0x20 [dm_multipath]
 [<ffffffffa0170da3>] map_request+0x43/0x210 [dm_mod]
 [<ffffffffa0170f8d>] map_tio_request+0x1d/0x40 [dm_mod]
 [<ffffffff81075a0d>] kthread_worker_fn+0x7d/0x1a0
 [<ffffffff8107591a>] kthread+0xea/0x100
 [<ffffffff81578c7f>] ret_from_fork+0x3f/0x70

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 drivers/scsi/scsi_lib.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 8106515..8f264a0 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1770,13 +1770,14 @@ static void scsi_request_fn(struct request_queue *q)
 	struct Scsi_Host *shost;
 	struct scsi_cmnd *cmd;
 	struct request *req;
+	int i;
 
 	/*
-	 * To start with, we keep looping until the queue is empty, or until
-	 * the host is no longer able to accept any more requests.
+	 * Loop until the queue is empty, until the host is no longer able to
+	 * accept any more requests or until 64 requests have been processed.
 	 */
 	shost = sdev->host;
-	for (;;) {
+	for (i = 64; i > 0; i--) {
 		int rtn;
 		/*
 		 * get next queueable request.  We do this early to make sure
@@ -1861,6 +1862,9 @@ static void scsi_request_fn(struct request_queue *q)
 		spin_lock_irq(q->queue_lock);
 	}
 
+	if (unlikely(i == 0))
+		blk_delay_queue(q, 0);
+
 	return;
 
  host_not_ready:
-- 
2.7.3