[PATCH v7 0/7] x86,fs/resctrl: Fix long-standing issues

[PATCH v7 0/7] x86,fs/resctrl: Fix long-standing issues

[Reinette Chatre]

v6: https://lore.kernel.org/lkml/cover.1783377598.git.reinette.chatre@intel.com/
v5: https://lore.kernel.org/lkml/cover.1781029125.git.reinette.chatre@intel.com/
v4: https://lore.kernel.org/lkml/cover.1780456704.git.reinette.chatre@intel.com/
v3: https://lore.kernel.org/lkml/cover.1779476724.git.reinette.chatre@intel.com/
v2: https://lore.kernel.org/lkml/20260515193944.15114-1-tony.luck@intel.com/
v1: https://lore.kernel.org/all/20260508182143.14592-1-tony.luck@intel.com/

While reviewing the AET series [1] Sashiko reported a deadlock during mount,
and a use-after-free when an L3 domain is removed during CPU offline. More issues
were uncovered as fixes were developed and reviewed. While the goal is to
fix all issues the races surrounding pseudo-locked regions are not yet
solved and have been removed from this series (last appearance was in V3 of
this series).

Applies against v7.2-rc3.

Changes since V6:
- Drop first three patches that are in v7.2-rc3.
- Remove extra blank lines. (Tony)
- No functional changes.

Changes since V5:
- Drop patch #1 (x86,fs/resctrl: Prevent out-of-bounds access while offlining
  CPU when SNC enabled) that can be found in v7.2-rc2.
- Re-order remaining patches so that stable candidate patches are at
  beginning of series. The stable candidates are:
  Patch 1: fs/resctrl: Free mon_data structures on rdt_get_tree() failure
  Patch 2: fs/resctrl: Fix use-after-free during unmount
  Patch 3: fs/resctrl: Fix double-add of pseudo-locked region's RMID to free list
- To support the backporting to stable patch #1 adds a forward declaration
  that is removed in patch #5 that moves the actual functions to avoid too many
  forward declarations.
- The end result of changes since v5: v6 net changes are identical to V5
  changes.

Changes since V4:
- Add new fix to prevent out-of-bouds read when SNC is enabled and domain
  with busy RMID goes offline.
- Add substitute for "is domain going offline" check to workers to avoid
  reading any event counters on soon-to-be-offline domain since its
  cpu_mask is empty and reading an event counter on an SNC enabled system
  depends on knowing a CPU associated with the domain.

Changes since V3:
- Drop majority of pseudo-locking fixes, only keep the double free/double
  list add fix.
- Add patch to help document safe RCU list traversal.
- See individual patches for detailed changes.

[1] https://sashiko.dev/#/patchset/20260429184858.36423-1-tony.luck%40intel.com

Reinette Chatre (6):
  x86,fs/resctrl: Document safe RCU list traversal
  fs/resctrl: Fix deadlock on errors during mount
  fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()
  fs/resctrl: Prevent deadlock and use-after-free in info file handlers
  x86/resctrl: Ensure domain fully initialized before placed on RCU list
  fs/resctrl: Fix UAF from worker threads when domains are removed

Tony Luck (1):
  fs/resctrl: Move functions to avoid forward references in subsequent
    fixes

 arch/x86/kernel/cpu/resctrl/core.c        |  18 +-
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c |   4 +-
 arch/x86/kernel/cpu/resctrl/intel_aet.c   |   5 +-
 arch/x86/kernel/cpu/resctrl/monitor.c     |   2 +-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    |   4 +-
 fs/resctrl/ctrlmondata.c                  |  50 +-
 fs/resctrl/internal.h                     |   3 +-
 fs/resctrl/monitor.c                      | 131 ++--
 fs/resctrl/pseudo_lock.c                  |   2 +-
 fs/resctrl/rdtgroup.c                     | 858 +++++++++++++---------
 10 files changed, 660 insertions(+), 417 deletions(-)


base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
-- 
2.54.0

[PATCH v7 1/7] x86,fs/resctrl: Document safe RCU list traversal

[Reinette Chatre]

rdt_resource::ctrl_domains and rdt_resource::mon_domains are RCU lists with
entries added and removed by architecture from CPU hotplug callbacks that
are run with cpus_write_lock() held. These lists can be traversed safely
from resctrl fs by either holding cpus_read_lock() or relying on an RCU
read-side critical section.

resctrl fs traversals of rdt_resource::ctrl_domains and
rdt_resource::mon_domains are done using list_for_each_entry() with
cpus_read_lock() held. Similarly, x86 architecture callbacks use
list_for_each_entry() expecting that resctrl fs makes the call with
cpus_read_lock() held. Inconsistently, a lockdep_assert_cpus_held() precedes
the list_for_each_entry() call with varying distance to document this safe
RCU list traversal.

In preparation for an upcoming traversal of rdt_resource::ctrl_domains that
needs to be done from RCU read-side critical section there is a requirement
for developers to always know exactly in which context the list is being
traversed.

Replace the list_for_each_entry() traversals of RCU list with
list_for_each_entry_rcu() to document that an RCU list is being traversed
while making use of the built-in lockdep expression that additionally
documents that it is cpus_read_lock() that enables the list to be
traversed from non-RCU protection. Only revert to documenting the
safety of traversal using a comment when lockdep does not have needed
visibility in functions called via smp_call*().

The lockdep expression within list_for_each_entry_rcu() depends on
RCU_EXPERT that is not set in a typical debug kernel so keep the existing
lockdep_assert_cpus_held() that is active with CONFIG_LOCKDEP=y found in
typical debug kernel.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changes since v3:
- New patch.
---
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c |  4 ++--
 arch/x86/kernel/cpu/resctrl/monitor.c     |  2 +-
 arch/x86/kernel/cpu/resctrl/rdtgroup.c    |  4 ++--
 fs/resctrl/ctrlmondata.c                  | 12 +++++++-----
 fs/resctrl/monitor.c                      | 23 +++++++++++++---------
 fs/resctrl/pseudo_lock.c                  |  2 +-
 fs/resctrl/rdtgroup.c                     | 24 +++++++++++------------
 7 files changed, 39 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index b20e705606b8..e74f1ed54b86 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -53,7 +53,7 @@ int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid)
 	/* Walking r->domains, ensure it can't race with cpuhp */
 	lockdep_assert_cpus_held();
 
-	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		hw_dom = resctrl_to_arch_ctrl_dom(d);
 		msr_param.res = NULL;
 		for (t = 0; t < CDP_NUM_TYPES; t++) {
@@ -115,7 +115,7 @@ static void _resctrl_sdciae_enable(struct rdt_resource *r, bool enable)
 	lockdep_assert_cpus_held();
 
 	/* Update MSR_IA32_L3_QOS_EXT_CFG MSR on all the CPUs in all domains */
-	list_for_each_entry(d, &r->ctrl_domains, hdr.list)
+	list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held())
 		on_each_cpu_mask(&d->hdr.cpu_mask, resctrl_sdciae_set_one_amd, &enable, 1);
 }
 
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index 569894d6e5c8..430b8fae0b77 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -510,7 +510,7 @@ static void _resctrl_abmc_enable(struct rdt_resource *r, bool enable)
 
 	lockdep_assert_cpus_held();
 
-	list_for_each_entry(d, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		on_each_cpu_mask(&d->hdr.cpu_mask, resctrl_abmc_set_one_amd,
 				 &enable, 1);
 		resctrl_arch_reset_rmid_all(r, d);
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index 885026468440..5ffa39fa86fa 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -151,7 +151,7 @@ static int set_cache_qos_cfg(int level, bool enable)
 		return -ENOMEM;
 
 	r_l = &rdt_resources_all[level].r_resctrl;
-	list_for_each_entry(d, &r_l->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r_l->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (r_l->cache.arch_has_per_cpu_cfg)
 			/* Pick all the CPUs in the domain instance */
 			for_each_cpu(cpu, &d->hdr.cpu_mask)
@@ -249,7 +249,7 @@ void resctrl_arch_reset_all_ctrls(struct rdt_resource *r)
 	 * CBMs in all ctrl_domains to the maximum mask value. Pick one CPU
 	 * from each domain to update the MSRs below.
 	 */
-	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		hw_dom = resctrl_to_arch_ctrl_dom(d);
 
 		for (i = 0; i < hw_res->num_closid; i++)
diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
index 9a7dfc48cb2e..f33712c17d38 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -261,7 +261,7 @@ static int parse_line(char *line, struct resctrl_schema *s,
 		return -EINVAL;
 	}
 	dom = strim(dom);
-	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (d->hdr.id == dom_id) {
 			data.buf = dom;
 			data.closid = rdtgrp->closid;
@@ -397,7 +397,7 @@ static void show_doms(struct seq_file *s, struct resctrl_schema *schema,
 
 	if (resource_name)
 		seq_printf(s, "%*s:", max_name_width, resource_name);
-	list_for_each_entry(dom, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(dom, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (sep)
 			seq_puts(s, ";");
 
@@ -535,6 +535,8 @@ struct rdt_domain_hdr *resctrl_find_domain(struct list_head *h, int id,
 	struct rdt_domain_hdr *d;
 	struct list_head *l;
 
+	lockdep_assert_cpus_held();
+
 	list_for_each(l, h) {
 		d = list_entry(l, struct rdt_domain_hdr, list);
 		/* When id is found, return its domain. */
@@ -717,7 +719,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 		 * struct mon_data. Search all domains in the resource for
 		 * one that matches this cache id.
 		 */
-		list_for_each_entry(d, &r->mon_domains, hdr.list) {
+		list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 			if (d->ci_id == domid) {
 				cpu = cpumask_any(&d->hdr.cpu_mask);
 				ci = get_cpu_cacheinfo_level(cpu, RESCTRL_L3_CACHE);
@@ -817,7 +819,7 @@ static int resctrl_io_alloc_init_cbm(struct resctrl_schema *s, u32 closid)
 	/* Keep CDP_CODE and CDP_DATA of io_alloc CLOSID's CBM in sync. */
 	if (resctrl_arch_get_cdp_enabled(r->rid)) {
 		peer_type = resctrl_peer_type(s->conf_type);
-		list_for_each_entry(d, &s->res->ctrl_domains, hdr.list)
+		list_for_each_entry_rcu(d, &s->res->ctrl_domains, hdr.list, lockdep_is_cpus_held())
 			memcpy(&d->staged_config[peer_type],
 			       &d->staged_config[s->conf_type],
 			       sizeof(d->staged_config[0]));
@@ -980,7 +982,7 @@ static int resctrl_io_alloc_parse_line(char *line,  struct rdt_resource *r,
 	}
 
 	dom = strim(dom);
-	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (update_all || d->hdr.id == dom_id) {
 			data.buf = dom;
 			data.mode = RDT_MODE_SHAREABLE;
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index a932a1fea818..2dacb589625d 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -309,7 +309,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 	idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
 
 	entry->busy = 0;
-	list_for_each_entry(d, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		/*
 		 * For the first limbo RMID in the domain,
 		 * setup up the limbo worker.
@@ -507,6 +507,11 @@ static int __l3_mon_event_count_sum(struct rdtgroup *rdtgrp, struct rmid_read *r
 	 * all domains fail for any reason.
 	 */
 	ret = -EINVAL;
+	/*
+	 * RCU list being traversed with CPU hotplug lock held. lockdep
+	 * unable to help prove this here since this work is scheduled via
+	 * smp_call*(). Not called from MBM overflow handler.
+	 */
 	list_for_each_entry(d, &rr->r->mon_domains, hdr.list) {
 		if (d->ci_id != rr->ci->id)
 			continue;
@@ -1231,7 +1236,7 @@ static int rdtgroup_assign_cntr_event(struct rdt_l3_mon_domain *d, struct rdtgro
 	int ret = 0;
 
 	if (!d) {
-		list_for_each_entry(d, &r->mon_domains, hdr.list) {
+		list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 			int err;
 
 			err = rdtgroup_alloc_assign_cntr(r, d, rdtgrp, mevt);
@@ -1303,7 +1308,7 @@ static void rdtgroup_unassign_cntr_event(struct rdt_l3_mon_domain *d, struct rdt
 	struct rdt_resource *r = resctrl_arch_get_resource(mevt->rid);
 
 	if (!d) {
-		list_for_each_entry(d, &r->mon_domains, hdr.list)
+		list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held())
 			rdtgroup_free_unassign_cntr(r, d, rdtgrp, mevt);
 	} else {
 		rdtgroup_free_unassign_cntr(r, d, rdtgrp, mevt);
@@ -1375,7 +1380,7 @@ static void rdtgroup_update_cntr_event(struct rdt_resource *r, struct rdtgroup *
 	struct rdt_l3_mon_domain *d;
 	int cntr_id;
 
-	list_for_each_entry(d, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		cntr_id = mbm_cntr_get(r, d, rdtgrp, evtid);
 		if (cntr_id >= 0)
 			rdtgroup_assign_cntr(r, d, evtid, rdtgrp->mon.rmid,
@@ -1545,7 +1550,7 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
 		/*
 		 * Reset all the non-achitectural RMID state and assignable counters.
 		 */
-		list_for_each_entry(d, &r->mon_domains, hdr.list) {
+		list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 			mbm_cntr_free_all(r, d);
 			resctrl_reset_rmid_all(r, d);
 		}
@@ -1568,7 +1573,7 @@ int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
 	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
 
-	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (sep)
 			seq_putc(s, ';');
 
@@ -1602,7 +1607,7 @@ int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of,
 		goto out_unlock;
 	}
 
-	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (sep)
 			seq_putc(s, ';');
 
@@ -1652,7 +1657,7 @@ int mbm_L3_assignments_show(struct kernfs_open_file *of, struct seq_file *s, voi
 
 		sep = false;
 		seq_printf(s, "%s:", mevt->name);
-		list_for_each_entry(d, &r->mon_domains, hdr.list) {
+		list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 			if (sep)
 				seq_putc(s, ';');
 
@@ -1750,7 +1755,7 @@ static int resctrl_parse_mbm_assignment(struct rdt_resource *r, struct rdtgroup
 	}
 
 	/* Verify if the dom_id is valid */
-	list_for_each_entry(d, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (d->hdr.id == dom_id) {
 			ret = rdtgroup_modify_assign_state(dom_str, d, rdtgrp, mevt);
 			if (ret) {
diff --git a/fs/resctrl/pseudo_lock.c b/fs/resctrl/pseudo_lock.c
index d1cb0986006e..dea2b4bf966f 100644
--- a/fs/resctrl/pseudo_lock.c
+++ b/fs/resctrl/pseudo_lock.c
@@ -656,7 +656,7 @@ bool rdtgroup_pseudo_locked_in_hierarchy(struct rdt_ctrl_domain *d)
 	 * associated with them.
 	 */
 	for_each_alloc_capable_rdt_resource(r) {
-		list_for_each_entry(d_i, &r->ctrl_domains, hdr.list) {
+		list_for_each_entry_rcu(d_i, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 			if (d_i->plr)
 				cpumask_or(cpu_with_psl, cpu_with_psl,
 					   &d_i->hdr.cpu_mask);
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index cc9966ff6cdf..5a0d69636d87 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -119,7 +119,7 @@ void rdt_staged_configs_clear(void)
 	lockdep_assert_held(&rdtgroup_mutex);
 
 	for_each_alloc_capable_rdt_resource(r) {
-		list_for_each_entry(dom, &r->ctrl_domains, hdr.list)
+		list_for_each_entry_rcu(dom, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held())
 			memset(dom->staged_config, 0, sizeof(dom->staged_config));
 	}
 }
@@ -1071,7 +1071,7 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
 
 	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
-	list_for_each_entry(dom, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(dom, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (sep)
 			seq_putc(seq, ';');
 		hw_shareable = r->cache.shareable_bits;
@@ -1423,7 +1423,7 @@ static bool rdtgroup_mode_test_exclusive(struct rdtgroup *rdtgrp)
 		if (r->rid == RDT_RESOURCE_MBA || r->rid == RDT_RESOURCE_SMBA)
 			continue;
 		has_cache = true;
-		list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+		list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 			ctrl = resctrl_arch_get_config(r, d, closid,
 						       s->conf_type);
 			if (rdtgroup_cbm_overlaps(s, d, ctrl, closid, false)) {
@@ -1612,7 +1612,7 @@ static int rdtgroup_size_show(struct kernfs_open_file *of,
 		type = schema->conf_type;
 		sep = false;
 		seq_printf(s, "%*s:", max_name_width, schema->name);
-		list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+		list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 			if (sep)
 				seq_putc(s, ';');
 			if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
@@ -1657,7 +1657,7 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
 	cpus_read_lock();
 	mutex_lock(&rdtgroup_mutex);
 
-	list_for_each_entry(dom, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (sep)
 			seq_puts(s, ";");
 
@@ -1771,7 +1771,7 @@ static int mon_config_write(struct rdt_resource *r, char *tok, u32 evtid)
 		return -EINVAL;
 	}
 
-	list_for_each_entry(d, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (d->hdr.id == dom_id) {
 			mbm_config_write_domain(r, d, evtid, val);
 			goto next;
@@ -2562,7 +2562,7 @@ static int set_mba_sc(bool mba_sc)
 
 	rdtgroup_default.mba_mbps_event = mba_mbps_default_event;
 
-	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		for (i = 0; i < num_closid; i++)
 			d->mbps_val[i] = MBA_MAX_MBPS;
 	}
@@ -2893,7 +2893,7 @@ static int rdt_get_tree(struct fs_context *fc)
 
 	if (resctrl_is_mbm_enabled()) {
 		r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
-		list_for_each_entry(dom, &r->mon_domains, hdr.list)
+		list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held())
 			mbm_setup_overflow_handler(dom, MBM_OVERFLOW_INTERVAL,
 						   RESCTRL_PICK_ANY_CPU);
 	}
@@ -3453,7 +3453,7 @@ static int mkdir_mondata_subdir_alldom(struct kernfs_node *parent_kn,
 	/* Walking r->domains, ensure it can't race with cpuhp */
 	lockdep_assert_cpus_held();
 
-	list_for_each_entry(hdr, &r->mon_domains, list) {
+	list_for_each_entry_rcu(hdr, &r->mon_domains, list, lockdep_is_cpus_held()) {
 		ret = mkdir_mondata_subdir(parent_kn, hdr, r, prgrp);
 		if (ret)
 			return ret;
@@ -3638,7 +3638,7 @@ int rdtgroup_init_cat(struct resctrl_schema *s, u32 closid)
 	struct rdt_ctrl_domain *d;
 	int ret;
 
-	list_for_each_entry(d, &s->res->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &s->res->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		ret = __init_one_rdt_domain(d, s, closid);
 		if (ret < 0)
 			return ret;
@@ -3653,7 +3653,7 @@ static void rdtgroup_init_mba(struct rdt_resource *r, u32 closid)
 	struct resctrl_staged_config *cfg;
 	struct rdt_ctrl_domain *d;
 
-	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (is_mba_sc(r)) {
 			d->mbps_val[closid] = MBA_MAX_MBPS;
 			continue;
@@ -4525,7 +4525,7 @@ static struct rdt_l3_mon_domain *get_mon_domain_from_cpu(int cpu,
 
 	lockdep_assert_cpus_held();
 
-	list_for_each_entry(d, &r->mon_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		/* Find the domain that contains this CPU */
 		if (cpumask_test_cpu(cpu, &d->hdr.cpu_mask))
 			return d;
-- 
2.54.0

[PATCH v7 2/7] fs/resctrl: Move functions to avoid forward references in subsequent fixes

[Reinette Chatre]

From: Tony Luck <tony.luck@intel.com>

rdt_get_tree() manages resctrl fs mount and rdt_kill_sb() manages resctrl
fs unmount.

There is significant overlap between error cleanup during resctrl mount
failure and cleanup on resctrl unmount yet the cleanup is not done
consistently in these two flows.

Pull some cleanup functions before rdt_get_tree() in preparation for
a new helper that can be shared between mount and unmount.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since V2:
- Rewrite changelog.

Changes since V3:
- Add Ben's Reviewed-by tag.

Changes since V5:
- Remove mon_put_kn_priv() forward declaration added in v6 to support
  backporting of portion of series.
---
 fs/resctrl/rdtgroup.c | 384 +++++++++++++++++++++---------------------
 1 file changed, 191 insertions(+), 193 deletions(-)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 5a0d69636d87..9804e40ad36d 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -74,8 +74,6 @@ static int rdtgroup_setup_root(struct rdt_fs_context *ctx);
 
 static void rdtgroup_destroy_root(void);
 
-static void mon_put_kn_priv(void);
-
 struct dentry *debugfs_resctrl;
 
 /*
@@ -2800,6 +2798,197 @@ static void schemata_list_destroy(void)
 	}
 }
 
+/*
+ * Move tasks from one to the other group. If @from is NULL, then all tasks
+ * in the systems are moved unconditionally (used for teardown).
+ *
+ * If @mask is not NULL the cpus on which moved tasks are running are set
+ * in that mask so the update smp function call is restricted to affected
+ * cpus.
+ */
+static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
+				 struct cpumask *mask)
+{
+	struct task_struct *p, *t;
+
+	read_lock(&tasklist_lock);
+	for_each_process_thread(p, t) {
+		if (!from || is_closid_match(t, from) ||
+		    is_rmid_match(t, from)) {
+			resctrl_arch_set_closid_rmid(t, to->closid,
+						     to->mon.rmid);
+
+			/*
+			 * Order the closid/rmid stores above before the loads
+			 * in task_curr(). This pairs with the full barrier
+			 * between the rq->curr update and
+			 * resctrl_arch_sched_in() during context switch.
+			 */
+			smp_mb();
+
+			/*
+			 * If the task is on a CPU, set the CPU in the mask.
+			 * The detection is inaccurate as tasks might move or
+			 * schedule before the smp function call takes place.
+			 * In such a case the function call is pointless, but
+			 * there is no other side effect.
+			 */
+			if (IS_ENABLED(CONFIG_SMP) && mask && task_curr(t))
+				cpumask_set_cpu(task_cpu(t), mask);
+		}
+	}
+	read_unlock(&tasklist_lock);
+}
+
+static void free_all_child_rdtgrp(struct rdtgroup *rdtgrp)
+{
+	struct rdtgroup *sentry, *stmp;
+	struct list_head *head;
+
+	head = &rdtgrp->mon.crdtgrp_list;
+	list_for_each_entry_safe(sentry, stmp, head, mon.crdtgrp_list) {
+		rdtgroup_unassign_cntrs(sentry);
+		free_rmid(sentry->closid, sentry->mon.rmid);
+		list_del(&sentry->mon.crdtgrp_list);
+
+		if (atomic_read(&sentry->waitcount) != 0)
+			sentry->flags = RDT_DELETED;
+		else
+			rdtgroup_remove(sentry);
+	}
+}
+
+/*
+ * Forcibly remove all of subdirectories under root.
+ */
+static void rmdir_all_sub(void)
+{
+	struct rdtgroup *rdtgrp, *tmp;
+
+	/* Move all tasks to the default resource group */
+	rdt_move_group_tasks(NULL, &rdtgroup_default, NULL);
+
+	list_for_each_entry_safe(rdtgrp, tmp, &rdt_all_groups, rdtgroup_list) {
+		/* Free any child rmids */
+		free_all_child_rdtgrp(rdtgrp);
+
+		/* Remove each rdtgroup other than root */
+		if (rdtgrp == &rdtgroup_default)
+			continue;
+
+		/*
+		 * Give any CPUs back to the default group. We cannot copy
+		 * cpu_online_mask because a CPU might have executed the
+		 * offline callback already, but is still marked online.
+		 */
+		cpumask_or(&rdtgroup_default.cpu_mask,
+			   &rdtgroup_default.cpu_mask, &rdtgrp->cpu_mask);
+
+		rdtgroup_unassign_cntrs(rdtgrp);
+
+		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP ||
+		    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
+			rdtgroup_pseudo_lock_remove(rdtgrp);
+		} else {
+			/* Pseudo-locked group's RMID is freed during setup. */
+			free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
+		}
+
+		kernfs_remove(rdtgrp->kn);
+		list_del(&rdtgrp->rdtgroup_list);
+
+		if (atomic_read(&rdtgrp->waitcount) != 0)
+			rdtgrp->flags = RDT_DELETED;
+		else
+			rdtgroup_remove(rdtgrp);
+	}
+	/* Notify online CPUs to update per cpu storage and PQR_ASSOC MSR */
+	update_closid_rmid(cpu_online_mask, &rdtgroup_default);
+
+	kernfs_remove(kn_info);
+	kernfs_remove(kn_mongrp);
+	kernfs_remove(kn_mondata);
+}
+
+/**
+ * mon_get_kn_priv() - Get the mon_data priv data for this event.
+ *
+ * The same values are used across the mon_data directories of all control and
+ * monitor groups for the same event in the same domain. Keep a list of
+ * allocated structures and re-use an existing one with the same values for
+ * @rid, @domid, etc.
+ *
+ * @rid:    The resource id for the event file being created.
+ * @domid:  The domain id for the event file being created.
+ * @mevt:   The type of event file being created.
+ * @do_sum: Whether SNC summing monitors are being created. Only set
+ *	    when @rid == RDT_RESOURCE_L3.
+ *
+ * Return: Pointer to mon_data private data of the event, NULL on failure.
+ */
+static struct mon_data *mon_get_kn_priv(enum resctrl_res_level rid, int domid,
+					struct mon_evt *mevt,
+					bool do_sum)
+{
+	struct mon_data *priv;
+
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	list_for_each_entry(priv, &mon_data_kn_priv_list, list) {
+		if (priv->rid == rid && priv->domid == domid &&
+		    priv->sum == do_sum && priv->evt == mevt)
+			return priv;
+	}
+
+	priv = kzalloc_obj(*priv);
+	if (!priv)
+		return NULL;
+
+	priv->rid = rid;
+	priv->domid = domid;
+	priv->sum = do_sum;
+	priv->evt = mevt;
+	list_add_tail(&priv->list, &mon_data_kn_priv_list);
+
+	return priv;
+}
+
+/**
+ * mon_put_kn_priv() - Free all allocated mon_data structures.
+ *
+ * Called when resctrl file system is unmounted.
+ */
+static void mon_put_kn_priv(void)
+{
+	struct mon_data *priv, *tmp;
+
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	list_for_each_entry_safe(priv, tmp, &mon_data_kn_priv_list, list) {
+		list_del(&priv->list);
+		kfree(priv);
+	}
+}
+
+static void resctrl_fs_teardown(void)
+{
+	lockdep_assert_held(&rdtgroup_mutex);
+
+	/* Cleared by rdtgroup_destroy_root() */
+	if (!rdtgroup_default.kn)
+		return;
+
+	rmdir_all_sub();
+	rdtgroup_unassign_cntrs(&rdtgroup_default);
+	mon_put_kn_priv();
+	rdt_pseudo_lock_release();
+	rdtgroup_default.mode = RDT_MODE_SHAREABLE;
+	rdtgroup_default.flags = RDT_DELETED;
+	closid_exit();
+	schemata_list_destroy();
+	rdtgroup_destroy_root();
+}
+
 static int rdt_get_tree(struct fs_context *fc)
 {
 	struct rdt_fs_context *ctx = rdt_fc2context(fc);
@@ -3006,197 +3195,6 @@ static int rdt_init_fs_context(struct fs_context *fc)
 	return 0;
 }
 
-/*
- * Move tasks from one to the other group. If @from is NULL, then all tasks
- * in the systems are moved unconditionally (used for teardown).
- *
- * If @mask is not NULL the cpus on which moved tasks are running are set
- * in that mask so the update smp function call is restricted to affected
- * cpus.
- */
-static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to,
-				 struct cpumask *mask)
-{
-	struct task_struct *p, *t;
-
-	read_lock(&tasklist_lock);
-	for_each_process_thread(p, t) {
-		if (!from || is_closid_match(t, from) ||
-		    is_rmid_match(t, from)) {
-			resctrl_arch_set_closid_rmid(t, to->closid,
-						     to->mon.rmid);
-
-			/*
-			 * Order the closid/rmid stores above before the loads
-			 * in task_curr(). This pairs with the full barrier
-			 * between the rq->curr update and
-			 * resctrl_arch_sched_in() during context switch.
-			 */
-			smp_mb();
-
-			/*
-			 * If the task is on a CPU, set the CPU in the mask.
-			 * The detection is inaccurate as tasks might move or
-			 * schedule before the smp function call takes place.
-			 * In such a case the function call is pointless, but
-			 * there is no other side effect.
-			 */
-			if (IS_ENABLED(CONFIG_SMP) && mask && task_curr(t))
-				cpumask_set_cpu(task_cpu(t), mask);
-		}
-	}
-	read_unlock(&tasklist_lock);
-}
-
-static void free_all_child_rdtgrp(struct rdtgroup *rdtgrp)
-{
-	struct rdtgroup *sentry, *stmp;
-	struct list_head *head;
-
-	head = &rdtgrp->mon.crdtgrp_list;
-	list_for_each_entry_safe(sentry, stmp, head, mon.crdtgrp_list) {
-		rdtgroup_unassign_cntrs(sentry);
-		free_rmid(sentry->closid, sentry->mon.rmid);
-		list_del(&sentry->mon.crdtgrp_list);
-
-		if (atomic_read(&sentry->waitcount) != 0)
-			sentry->flags = RDT_DELETED;
-		else
-			rdtgroup_remove(sentry);
-	}
-}
-
-/*
- * Forcibly remove all of subdirectories under root.
- */
-static void rmdir_all_sub(void)
-{
-	struct rdtgroup *rdtgrp, *tmp;
-
-	/* Move all tasks to the default resource group */
-	rdt_move_group_tasks(NULL, &rdtgroup_default, NULL);
-
-	list_for_each_entry_safe(rdtgrp, tmp, &rdt_all_groups, rdtgroup_list) {
-		/* Free any child rmids */
-		free_all_child_rdtgrp(rdtgrp);
-
-		/* Remove each rdtgroup other than root */
-		if (rdtgrp == &rdtgroup_default)
-			continue;
-
-		/*
-		 * Give any CPUs back to the default group. We cannot copy
-		 * cpu_online_mask because a CPU might have executed the
-		 * offline callback already, but is still marked online.
-		 */
-		cpumask_or(&rdtgroup_default.cpu_mask,
-			   &rdtgroup_default.cpu_mask, &rdtgrp->cpu_mask);
-
-		rdtgroup_unassign_cntrs(rdtgrp);
-
-		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP ||
-		    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED) {
-			rdtgroup_pseudo_lock_remove(rdtgrp);
-		} else {
-			/* Pseudo-locked group's RMID is freed during setup. */
-			free_rmid(rdtgrp->closid, rdtgrp->mon.rmid);
-		}
-
-		kernfs_remove(rdtgrp->kn);
-		list_del(&rdtgrp->rdtgroup_list);
-
-		if (atomic_read(&rdtgrp->waitcount) != 0)
-			rdtgrp->flags = RDT_DELETED;
-		else
-			rdtgroup_remove(rdtgrp);
-	}
-	/* Notify online CPUs to update per cpu storage and PQR_ASSOC MSR */
-	update_closid_rmid(cpu_online_mask, &rdtgroup_default);
-
-	kernfs_remove(kn_info);
-	kernfs_remove(kn_mongrp);
-	kernfs_remove(kn_mondata);
-}
-
-/**
- * mon_get_kn_priv() - Get the mon_data priv data for this event.
- *
- * The same values are used across the mon_data directories of all control and
- * monitor groups for the same event in the same domain. Keep a list of
- * allocated structures and re-use an existing one with the same values for
- * @rid, @domid, etc.
- *
- * @rid:    The resource id for the event file being created.
- * @domid:  The domain id for the event file being created.
- * @mevt:   The type of event file being created.
- * @do_sum: Whether SNC summing monitors are being created. Only set
- *	    when @rid == RDT_RESOURCE_L3.
- *
- * Return: Pointer to mon_data private data of the event, NULL on failure.
- */
-static struct mon_data *mon_get_kn_priv(enum resctrl_res_level rid, int domid,
-					struct mon_evt *mevt,
-					bool do_sum)
-{
-	struct mon_data *priv;
-
-	lockdep_assert_held(&rdtgroup_mutex);
-
-	list_for_each_entry(priv, &mon_data_kn_priv_list, list) {
-		if (priv->rid == rid && priv->domid == domid &&
-		    priv->sum == do_sum && priv->evt == mevt)
-			return priv;
-	}
-
-	priv = kzalloc_obj(*priv);
-	if (!priv)
-		return NULL;
-
-	priv->rid = rid;
-	priv->domid = domid;
-	priv->sum = do_sum;
-	priv->evt = mevt;
-	list_add_tail(&priv->list, &mon_data_kn_priv_list);
-
-	return priv;
-}
-
-/**
- * mon_put_kn_priv() - Free all allocated mon_data structures.
- *
- * Called when resctrl file system is unmounted.
- */
-static void mon_put_kn_priv(void)
-{
-	struct mon_data *priv, *tmp;
-
-	lockdep_assert_held(&rdtgroup_mutex);
-
-	list_for_each_entry_safe(priv, tmp, &mon_data_kn_priv_list, list) {
-		list_del(&priv->list);
-		kfree(priv);
-	}
-}
-
-static void resctrl_fs_teardown(void)
-{
-	lockdep_assert_held(&rdtgroup_mutex);
-
-	/* Cleared by rdtgroup_destroy_root() */
-	if (!rdtgroup_default.kn)
-		return;
-
-	rmdir_all_sub();
-	rdtgroup_unassign_cntrs(&rdtgroup_default);
-	mon_put_kn_priv();
-	rdt_pseudo_lock_release();
-	rdtgroup_default.mode = RDT_MODE_SHAREABLE;
-	rdtgroup_default.flags = RDT_DELETED;
-	closid_exit();
-	schemata_list_destroy();
-	rdtgroup_destroy_root();
-}
-
 static void rdt_kill_sb(struct super_block *sb)
 {
 	struct rdt_resource *r;
-- 
2.54.0

[PATCH v7 3/7] fs/resctrl: Fix deadlock on errors during mount

[Reinette Chatre]

rdt_get_tree() acquires rdtgroup_mutex before calling kernfs_get_tree(). If
superblock setup fails inside kernfs_get_tree(), the VFS calls .kill_sb()
(rdt_kill_sb()) on the same thread before kernfs_get_tree() returns.
rdt_kill_sb() unconditionally attempts to acquire rdtgroup_mutex and
deadlock occurs.

Since mount failure resulting from kernfs_get_tree() already calls the
resctrl fs unmount handler (rdt_kill_sb()) let both call the same helper
to make it clear both paths perform the same cleanup.

Call kernfs_get_tree() outside of locks. If kernfs_get_tree() fails and
ctx->kfc.new_sb_created is set, then rdt_kill_sb() has already been called
and no further cleanup is needed.

kernfs_get_tree() may set ctx->kfc.new_sb_created and then fail to obtain
an inode for the new kn, causing the rdt_kill_sb() path to run with one fewer
reference than required for the root to remain accessible in kernfs_kill_sb().
Add an extra hold on rdtgroup_default.kn to defend against this scenario
and ensure the root can be dereferenced safely from kernfs_kill_sb().

Dropping locks before kernfs_get_tree() creates a window where CPU hotplug
callbacks can race with the mount operation. Specifically, an online event
observing resctrl_mounted == true could concurrently append directories to
the unactivated kernfs tree, allocate mon_data structures, and arm background
workers.

This concurrency is safe because the mount has not yet returned to the VFS,
meaning userspace cannot interact with these transient files. If
kernfs_get_tree() subsequently fails, the standard resctrl_unmount() teardown
safely manages the concurrent modifications: any dynamically generated kernfs
nodes are removed, and the associated memory is freed. Any background
workers spawned by the hotplug event will naturally exit without re-arming
when they acquire rdtgroup_mutex and observe resctrl_mounted == false.

Fixes: 5ff193fbde20 ("x86/intel_rdt: Add basic resctrl filesystem support")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260429184858.36423-1-tony.luck%40intel.com [1]
Co-developed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: Chen Yu <yu.c.chen@intel.com>
---
Changes since V2:
- Switch to "Reported-by/Closes" in changelog

Changes since V3:
- Add Ben's Reviewed-by tag.
- Rework subject and changelog.
- s/root kn/root/ in comment. (Chenyu)
- Add Chenyu's Reviewed-by tag.
- Changelog grammar fixes.
- Add snippet to changelog about potential race with hotplug handlers.
---
 fs/resctrl/rdtgroup.c | 83 +++++++++++++++++++++++++++++--------------
 1 file changed, 56 insertions(+), 27 deletions(-)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 9804e40ad36d..ce964721ba8e 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -2989,10 +2989,34 @@ static void resctrl_fs_teardown(void)
 	rdtgroup_destroy_root();
 }
 
+static void resctrl_unmount(void)
+{
+	struct rdt_resource *r;
+
+	cpus_read_lock();
+	mutex_lock(&rdtgroup_mutex);
+
+	rdt_disable_ctx();
+
+	/* Put everything back to default values. */
+	for_each_alloc_capable_rdt_resource(r)
+		resctrl_arch_reset_all_ctrls(r);
+
+	resctrl_fs_teardown();
+	if (resctrl_arch_alloc_capable())
+		resctrl_arch_disable_alloc();
+	if (resctrl_arch_mon_capable())
+		resctrl_arch_disable_mon();
+	resctrl_mounted = false;
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+}
+
 static int rdt_get_tree(struct fs_context *fc)
 {
 	struct rdt_fs_context *ctx = rdt_fc2context(fc);
 	unsigned long flags = RFTYPE_CTRL_BASE;
+	struct kernfs_node *rdt_root_kn;
 	struct rdt_l3_mon_domain *dom;
 	struct rdt_resource *r;
 	int ret;
@@ -3068,10 +3092,6 @@ static int rdt_get_tree(struct fs_context *fc)
 	if (ret)
 		goto out_mondata;
 
-	ret = kernfs_get_tree(fc);
-	if (ret < 0)
-		goto out_psl;
-
 	if (resctrl_arch_alloc_capable())
 		resctrl_arch_enable_alloc();
 	if (resctrl_arch_mon_capable())
@@ -3087,10 +3107,38 @@ static int rdt_get_tree(struct fs_context *fc)
 						   RESCTRL_PICK_ANY_CPU);
 	}
 
-	goto out;
+	/*
+	 * Ensure root remains accessible after mutex is unlocked so that
+	 * kernfs_kill_sb() can run safely if called by kernfs_get_tree()'s
+	 * failure path after creating a superblock but before taking reference
+	 * on root kn (for example, if unable to get inode for root kn).
+	 */
+	kernfs_get(rdtgroup_default.kn);
+
+	/*
+	 * Make backup of the current root kn being created to be used in
+	 * kernfs_put(). The additional reference taken above will prevent the
+	 * kn from being freed before kernfs_kill_sb() can run but
+	 * rdtgroup_default.kn may be set to NULL via rdtgroup_destroy_root()
+	 * and its backing root (rdt_root) could be overwritten before
+	 * kernfs_put() can run.
+	 */
+	rdt_root_kn = rdtgroup_default.kn;
+
+	rdt_last_cmd_clear();
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+
+	ret = kernfs_get_tree(fc);
+	/*
+	 * resctrl can only be mounted once, new superblock only expected
+	 * to be created once.
+	 */
+	if (!ctx->kfc.new_sb_created)
+		resctrl_unmount();
+	kernfs_put(rdt_root_kn);
+	return ret;
 
-out_psl:
-	rdt_pseudo_lock_release();
 out_mondata:
 	if (resctrl_arch_mon_capable())
 		kernfs_remove(kn_mondata);
@@ -3110,7 +3158,6 @@ static int rdt_get_tree(struct fs_context *fc)
 out_root:
 	rdtgroup_destroy_root();
 out:
-	rdt_last_cmd_clear();
 	mutex_unlock(&rdtgroup_mutex);
 	cpus_read_unlock();
 	return ret;
@@ -3197,26 +3244,8 @@ static int rdt_init_fs_context(struct fs_context *fc)
 
 static void rdt_kill_sb(struct super_block *sb)
 {
-	struct rdt_resource *r;
-
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
-
-	rdt_disable_ctx();
-
-	/* Put everything back to default values. */
-	for_each_alloc_capable_rdt_resource(r)
-		resctrl_arch_reset_all_ctrls(r);
-
-	resctrl_fs_teardown();
-	if (resctrl_arch_alloc_capable())
-		resctrl_arch_disable_alloc();
-	if (resctrl_arch_mon_capable())
-		resctrl_arch_disable_mon();
-	resctrl_mounted = false;
+	resctrl_unmount();
 	kernfs_kill_sb(sb);
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
 }
 
 static struct file_system_type rdt_fs_type = {
-- 
2.54.0

[PATCH v7 4/7] fs/resctrl: Prevent use-after-free in rdtgroup_kn_put()

[Reinette Chatre]

A struct rdtgroup is reference counted via rdtgroup::waitcount. Callers
that need the structure to remain valid across a sleep (while waiting on
acquiring rdtgroup_mutex) take a reference with rdtgroup_kn_get() and
release it with rdtgroup_kn_put(). The release path is intended to serve
as the fallback freer: if the count drops to zero and the group has
already been marked RDT_DELETED, rdtgroup_kn_put() frees the structure.
The bulk teardown paths free_all_child_rdtgrp() and rmdir_all_sub()
resulting from a resctrl directory remove or resctrl fs unmount act as
the primary freer: they hold rdtgroup_mutex and free each rdtgroup whose
waitcount is zero, otherwise they set RDT_DELETED and leave the freeing
to the last waiter.

These two freers race. rdtgroup_kn_put() commits waitcount == 0 with
atomic_dec_and_test() outside rdtgroup_mutex, then reads rdtgroup::flags.
Between those two operations a concurrent caller of free_all_child_rdtgrp()
or rmdir_all_sub() (which holds the mutex) can observe waitcount == 0 via
atomic_read(), call rdtgroup_remove(), and kfree() the structure. The
subsequent read of rdtgroup::flags in rdtgroup_kn_put() is then a
use-after-free, and the structure may even be freed twice if the freed
memory happens to satisfy the RDT_DELETED flag check.

Replace the bare atomic_dec_and_test() with atomic_dec_and_mutex_lock()
so that the decrement-to-zero takes rdtgroup_mutex before the count
becomes globally visible. The inspection of rdtgroup::flags then runs
under the same mutex held by the bulk freers, making the two paths
mutually exclusive. The common case where the count does not reach
zero remains lock-free. Defer kernfs_unbreak_active_protection() until
after the mutex is dropped since kernfs active protections functionally
wrap rdtgroup_mutex. Remove resource group, which in turn drops its kernfs
reference, after kernfs protection is restored.

Fixes: b8511ccc75c0 ("x86/resctrl: Fix use-after-free when deleting resource groups")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260515193944.15114-1-tony.luck%40intel.com?part=1
Assisted-by: GitHub_Copilot:gemini-3.1-pro
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Ben Horgan <ben.horgan@arm.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
Changes since V2:
- New patch

Changes since V3:
- Add Ben's Reviewed-by tag.
- Add Tony's Reviewed-by tag.
---
 fs/resctrl/rdtgroup.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index ce964721ba8e..77c9d22017bc 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -2606,15 +2606,24 @@ static void rdtgroup_kn_get(struct rdtgroup *rdtgrp, struct kernfs_node *kn)
 
 static void rdtgroup_kn_put(struct rdtgroup *rdtgrp, struct kernfs_node *kn)
 {
-	if (atomic_dec_and_test(&rdtgrp->waitcount) &&
-	    (rdtgrp->flags & RDT_DELETED)) {
+	bool needs_free;
+
+	if (!atomic_dec_and_mutex_lock(&rdtgrp->waitcount, &rdtgroup_mutex)) {
+		kernfs_unbreak_active_protection(kn);
+		return;
+	}
+
+	needs_free = rdtgrp->flags & RDT_DELETED;
+
+	mutex_unlock(&rdtgroup_mutex);
+
+	kernfs_unbreak_active_protection(kn);
+
+	if (needs_free) {
 		if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP ||
 		    rdtgrp->mode == RDT_MODE_PSEUDO_LOCKED)
 			rdtgroup_pseudo_lock_remove(rdtgrp);
-		kernfs_unbreak_active_protection(kn);
 		rdtgroup_remove(rdtgrp);
-	} else {
-		kernfs_unbreak_active_protection(kn);
 	}
 }
 
-- 
2.54.0

[PATCH v7 5/7] fs/resctrl: Prevent deadlock and use-after-free in info file handlers

[Reinette Chatre]

resctrl provides files under the info/ directory to expose global
configuration and capabilities to userspace. These files are instantiated
statically during filesystem mount and expose data associated with internal
schema structures via kernfs private pointers.

A potential deadlock exists between userspace readers of these info files
and the unmount filesystem teardown process. Reading an info file invokes
kernfs which acquires an active reference, after which the handler typically
attempts to acquire the rdtgroup_mutex. Concurrently, unmounting the
filesystem holds the rdtgroup_mutex and then attempts to recursively
remove the info kernfs nodes involving kernfs_drain() which blocks until
all active references are released. Another problem exists where info files
might be accessed from an outdated mount if the filesystem is unmounted and
remounted during a reader's execution, leading to a use-after-free when
reading the now-deleted private schema data.

Introduce info_kn_lock() and info_kn_unlock() helpers to coordinate locking
across all info handlers. These helpers mirror similar logic used by resource
group handlers by deliberately breaking the kernfs active protection before
attempting to acquire the rdtgroup_mutex, preventing the deadlock. To guard
against the vulnerability from rapid mount cycling, info_kn_lock() securely
walks the parent lineage of the kernfs node under an RCU section to confirm
the node belongs to the globally active root before permitting the operation
to proceed. Convert all info file handlers to use this helper and only
de-reference the schema after it is determined safe to do so.

Make no attempt to output an error message to last_cmd_status on failure
since failure implies there is no filesystem with which to display the error
to user space.

Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260515193944.15114-1-tony.luck%40intel.com?part=3
Assisted-by: GitHub_Copilot:gemini-3.1-pro
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
---
Changes since V2:
- New patch

Changes since V3:
- Add Tony's Reviewed-by tag.
- Changelog grammar fixes.

Changes since V6:
- Remove extra blank lines. (Tony)
---
 fs/resctrl/ctrlmondata.c |  38 ++++----
 fs/resctrl/internal.h    |   3 +-
 fs/resctrl/monitor.c     |  48 +++++-----
 fs/resctrl/rdtgroup.c    | 192 +++++++++++++++++++++++++++++++--------
 4 files changed, 202 insertions(+), 79 deletions(-)

diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
index f33712c17d38..2b29fb5a8702 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -771,10 +771,12 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 int resctrl_io_alloc_show(struct kernfs_open_file *of, struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
+	r = s->res;
 	if (r->cache.io_alloc_capable) {
 		if (resctrl_arch_get_io_alloc_enabled(r))
 			seq_puts(seq, "enabled\n");
@@ -784,7 +786,7 @@ int resctrl_io_alloc_show(struct kernfs_open_file *of, struct seq_file *seq, voi
 		seq_puts(seq, "not supported\n");
 	}
 
-	mutex_unlock(&rdtgroup_mutex);
+	info_kn_unlock(of->kn);
 
 	return 0;
 }
@@ -849,7 +851,7 @@ ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
 			       size_t nbytes, loff_t off)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 	char const *grp_name;
 	u32 io_alloc_closid;
 	bool enable;
@@ -859,9 +861,10 @@ ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
 	if (ret)
 		return ret;
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
+	r = s->res;
 	rdt_last_cmd_clear();
 
 	if (!r->cache.io_alloc_capable) {
@@ -909,8 +912,7 @@ ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
 	}
 
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 
 	return ret ?: nbytes;
 }
@@ -918,14 +920,15 @@ ssize_t resctrl_io_alloc_write(struct kernfs_open_file *of, char *buf,
 int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of, struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 	int ret = 0;
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
 	rdt_last_cmd_clear();
 
+	r = s->res;
 	if (!r->cache.io_alloc_capable) {
 		rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);
 		ret = -ENODEV;
@@ -947,8 +950,7 @@ int resctrl_io_alloc_cbm_show(struct kernfs_open_file *of, struct seq_file *seq,
 	show_doms(seq, s, NULL, resctrl_io_alloc_closid(r));
 
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 	return ret;
 }
 
@@ -1015,7 +1017,7 @@ ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
 				   size_t nbytes, loff_t off)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 	u32 io_alloc_closid;
 	int ret = 0;
 
@@ -1025,10 +1027,11 @@ ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
 
 	buf[nbytes - 1] = '\0';
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	rdt_last_cmd_clear();
 
+	r = s->res;
 	if (!r->cache.io_alloc_capable) {
 		rdt_last_cmd_printf("io_alloc is not supported on %s\n", s->name);
 		ret = -ENODEV;
@@ -1053,8 +1056,7 @@ ssize_t resctrl_io_alloc_cbm_write(struct kernfs_open_file *of, char *buf,
 out_clear_configs:
 	rdt_staged_configs_clear();
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 
 	return ret ?: nbytes;
 }
diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 48af75b9dc85..e62a277dee85 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -335,8 +335,9 @@ __printf(1, 2)
 void rdt_last_cmd_printf(const char *fmt, ...);
 
 struct rdtgroup *rdtgroup_kn_lock_live(struct kernfs_node *kn);
-
 void rdtgroup_kn_unlock(struct kernfs_node *kn);
+bool info_kn_lock(struct kernfs_node *kn);
+void info_kn_unlock(struct kernfs_node *kn);
 
 int rdtgroup_kn_mode_restrict(struct rdtgroup *r, const char *name);
 
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 2dacb589625d..15e3eeddb6df 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1062,7 +1062,8 @@ int event_filter_show(struct kernfs_open_file *of, struct seq_file *seq, void *v
 	bool sep = false;
 	int ret = 0, i;
 
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	rdt_last_cmd_clear();
 
 	r = resctrl_arch_get_resource(mevt->rid);
@@ -1083,7 +1084,7 @@ int event_filter_show(struct kernfs_open_file *of, struct seq_file *seq, void *v
 	seq_putc(seq, '\n');
 
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
+	info_kn_unlock(of->kn);
 
 	return ret;
 }
@@ -1094,7 +1095,8 @@ int resctrl_mbm_assign_on_mkdir_show(struct kernfs_open_file *of, struct seq_fil
 	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
 	int ret = 0;
 
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	rdt_last_cmd_clear();
 
 	if (!resctrl_arch_mbm_cntr_assign_enabled(r)) {
@@ -1106,7 +1108,7 @@ int resctrl_mbm_assign_on_mkdir_show(struct kernfs_open_file *of, struct seq_fil
 	seq_printf(s, "%u\n", r->mon.mbm_assign_on_mkdir);
 
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
+	info_kn_unlock(of->kn);
 
 	return ret;
 }
@@ -1122,7 +1124,8 @@ ssize_t resctrl_mbm_assign_on_mkdir_write(struct kernfs_open_file *of, char *buf
 	if (ret)
 		return ret;
 
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	rdt_last_cmd_clear();
 
 	if (!resctrl_arch_mbm_cntr_assign_enabled(r)) {
@@ -1134,7 +1137,7 @@ ssize_t resctrl_mbm_assign_on_mkdir_write(struct kernfs_open_file *of, char *buf
 	r->mon.mbm_assign_on_mkdir = value;
 
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
+	info_kn_unlock(of->kn);
 
 	return ret ?: nbytes;
 }
@@ -1424,8 +1427,8 @@ ssize_t event_filter_write(struct kernfs_open_file *of, char *buf, size_t nbytes
 
 	buf[nbytes - 1] = '\0';
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
 	rdt_last_cmd_clear();
 
@@ -1448,8 +1451,7 @@ ssize_t event_filter_write(struct kernfs_open_file *of, char *buf, size_t nbytes
 	}
 
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 
 	return ret ?: nbytes;
 }
@@ -1460,7 +1462,8 @@ int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
 	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
 	bool enabled;
 
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	enabled = resctrl_arch_mbm_cntr_assign_enabled(r);
 
 	if (r->mon.mbm_cntr_assignable) {
@@ -1479,7 +1482,7 @@ int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
 		seq_puts(s, "[default]\n");
 	}
 
-	mutex_unlock(&rdtgroup_mutex);
+	info_kn_unlock(of->kn);
 
 	return 0;
 }
@@ -1498,8 +1501,8 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
 
 	buf[nbytes - 1] = '\0';
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
 	rdt_last_cmd_clear();
 
@@ -1557,8 +1560,7 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
 	}
 
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 
 	return ret ?: nbytes;
 }
@@ -1570,8 +1572,8 @@ int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
 	struct rdt_l3_mon_domain *dom;
 	bool sep = false;
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
 	list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (sep)
@@ -1582,8 +1584,7 @@ int resctrl_num_mbm_cntrs_show(struct kernfs_open_file *of,
 	}
 	seq_putc(s, '\n');
 
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 	return 0;
 }
 
@@ -1596,8 +1597,8 @@ int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of,
 	u32 cntrs, i;
 	int ret = 0;
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
 	rdt_last_cmd_clear();
 
@@ -1623,8 +1624,7 @@ int resctrl_available_mbm_cntrs_show(struct kernfs_open_file *of,
 	seq_putc(s, '\n');
 
 out_unlock:
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 
 	return ret;
 }
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 77c9d22017bc..2fd68733166c 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -977,13 +977,14 @@ static int rdt_last_cmd_status_show(struct kernfs_open_file *of,
 {
 	int len;
 
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	len = seq_buf_used(&last_cmd_status);
 	if (len)
 		seq_printf(seq, "%.*s", len, last_cmd_status_buf);
 	else
 		seq_puts(seq, "ok\n");
-	mutex_unlock(&rdtgroup_mutex);
+	info_kn_unlock(of->kn);
 	return 0;
 }
 
@@ -1002,7 +1003,11 @@ static int rdt_num_closids_show(struct kernfs_open_file *of,
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	seq_printf(seq, "%u\n", s->num_closid);
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1010,9 +1015,14 @@ static int rdt_default_ctrl_show(struct kernfs_open_file *of,
 				 struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+	r = s->res;
 	seq_printf(seq, "%x\n", resctrl_get_default_ctrl(r));
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1020,9 +1030,14 @@ static int rdt_min_cbm_bits_show(struct kernfs_open_file *of,
 				 struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+	r = s->res;
 	seq_printf(seq, "%u\n", r->cache.min_cbm_bits);
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1030,9 +1045,14 @@ static int rdt_shareable_bits_show(struct kernfs_open_file *of,
 				   struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+	r = s->res;
 	seq_printf(seq, "%x\n", r->cache.shareable_bits);
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1060,15 +1080,16 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
 	 */
 	unsigned long sw_shareable = 0, hw_shareable = 0;
 	unsigned long exclusive = 0, pseudo_locked = 0;
-	struct rdt_resource *r = s->res;
 	struct rdt_ctrl_domain *dom;
 	int i, hwb, swb, excl, psl;
+	struct rdt_resource *r;
 	enum rdtgrp_mode mode;
 	bool sep = false;
 	u32 ctrl_val;
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+	r = s->res;
 	list_for_each_entry_rcu(dom, &r->ctrl_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (sep)
 			seq_putc(seq, ';');
@@ -1144,8 +1165,7 @@ static int rdt_bit_usage_show(struct kernfs_open_file *of,
 		sep = true;
 	}
 	seq_putc(seq, '\n');
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 	return 0;
 }
 
@@ -1153,9 +1173,14 @@ static int rdt_min_bw_show(struct kernfs_open_file *of,
 			   struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+	r = s->res;
 	seq_printf(seq, "%u\n", r->membw.min_bw);
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1164,8 +1189,12 @@ static int rdt_num_rmids_show(struct kernfs_open_file *of,
 {
 	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	seq_printf(seq, "%u\n", r->mon.num_rmid);
 
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1175,6 +1204,8 @@ static int rdt_mon_features_show(struct kernfs_open_file *of,
 	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
 	struct mon_evt *mevt;
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	for_each_mon_event(mevt) {
 		if (mevt->rid != r->rid || !mevt->enabled)
 			continue;
@@ -1184,6 +1215,8 @@ static int rdt_mon_features_show(struct kernfs_open_file *of,
 			seq_printf(seq, "%s_config\n", mevt->name);
 	}
 
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1191,9 +1224,14 @@ static int rdt_bw_gran_show(struct kernfs_open_file *of,
 			    struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+	r = s->res;
 	seq_printf(seq, "%u\n", r->membw.bw_gran);
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1201,16 +1239,24 @@ static int rdt_delay_linear_show(struct kernfs_open_file *of,
 				 struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+	r = s->res;
 	seq_printf(seq, "%u\n", r->membw.delay_linear);
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
 static int max_threshold_occ_show(struct kernfs_open_file *of,
 				  struct seq_file *seq, void *v)
 {
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 	seq_printf(seq, "%u\n", resctrl_rmid_realloc_threshold);
+	info_kn_unlock(of->kn);
 
 	return 0;
 }
@@ -1219,22 +1265,28 @@ static int rdt_thread_throttle_mode_show(struct kernfs_open_file *of,
 					 struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
+
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
+	r = s->res;
 	switch (r->membw.throttle_mode) {
 	case THREAD_THROTTLE_PER_THREAD:
 		seq_puts(seq, "per-thread\n");
-		return 0;
+		break;
 	case THREAD_THROTTLE_MAX:
 		seq_puts(seq, "max\n");
-		return 0;
+		break;
 	case THREAD_THROTTLE_UNDEFINED:
 		seq_puts(seq, "undefined\n");
-		return 0;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		break;
 	}
 
-	WARN_ON_ONCE(1);
-
+	info_kn_unlock(of->kn);
 	return 0;
 }
 
@@ -1248,12 +1300,20 @@ static ssize_t max_threshold_occ_write(struct kernfs_open_file *of,
 	if (ret)
 		return ret;
 
-	if (bytes > resctrl_rmid_realloc_limit)
-		return -EINVAL;
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+
+	if (bytes > resctrl_rmid_realloc_limit) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
 
 	resctrl_rmid_realloc_threshold = resctrl_arch_round_mon_val(bytes);
 
-	return nbytes;
+out_unlock:
+	info_kn_unlock(of->kn);
+
+	return ret ?: nbytes;
 }
 
 /*
@@ -1293,10 +1353,15 @@ static int rdt_has_sparse_bitmasks_show(struct kernfs_open_file *of,
 					struct seq_file *seq, void *v)
 {
 	struct resctrl_schema *s = rdt_kn_parent_priv(of->kn);
-	struct rdt_resource *r = s->res;
+	struct rdt_resource *r;
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+	r = s->res;
 	seq_printf(seq, "%u\n", r->cache.arch_has_sparse_bitmasks);
 
+	info_kn_unlock(of->kn);
+
 	return 0;
 }
 
@@ -1652,8 +1717,8 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
 	struct rdt_l3_mon_domain *dom;
 	bool sep = false;
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	lockdep_assert_cpus_held();
+	lockdep_assert_held(&rdtgroup_mutex);
 
 	list_for_each_entry_rcu(dom, &r->mon_domains, hdr.list, lockdep_is_cpus_held()) {
 		if (sep)
@@ -1670,9 +1735,6 @@ static int mbm_config_show(struct seq_file *s, struct rdt_resource *r, u32 evtid
 	}
 	seq_puts(s, "\n");
 
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
-
 	return 0;
 }
 
@@ -1681,8 +1743,12 @@ static int mbm_total_bytes_config_show(struct kernfs_open_file *of,
 {
 	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+
 	mbm_config_show(seq, r, QOS_L3_MBM_TOTAL_EVENT_ID);
 
+	info_kn_unlock(of->kn);
 	return 0;
 }
 
@@ -1691,8 +1757,12 @@ static int mbm_local_bytes_config_show(struct kernfs_open_file *of,
 {
 	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
 
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
+
 	mbm_config_show(seq, r, QOS_L3_MBM_LOCAL_EVENT_ID);
 
+	info_kn_unlock(of->kn);
 	return 0;
 }
 
@@ -1790,8 +1860,8 @@ static ssize_t mbm_total_bytes_config_write(struct kernfs_open_file *of,
 	if (nbytes == 0 || buf[nbytes - 1] != '\n')
 		return -EINVAL;
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
 	rdt_last_cmd_clear();
 
@@ -1799,8 +1869,7 @@ static ssize_t mbm_total_bytes_config_write(struct kernfs_open_file *of,
 
 	ret = mon_config_write(r, buf, QOS_L3_MBM_TOTAL_EVENT_ID);
 
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 
 	return ret ?: nbytes;
 }
@@ -1816,8 +1885,8 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
 	if (nbytes == 0 || buf[nbytes - 1] != '\n')
 		return -EINVAL;
 
-	cpus_read_lock();
-	mutex_lock(&rdtgroup_mutex);
+	if (!info_kn_lock(of->kn))
+		return -ENOENT;
 
 	rdt_last_cmd_clear();
 
@@ -1825,8 +1894,7 @@ static ssize_t mbm_local_bytes_config_write(struct kernfs_open_file *of,
 
 	ret = mon_config_write(r, buf, QOS_L3_MBM_LOCAL_EVENT_ID);
 
-	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
+	info_kn_unlock(of->kn);
 
 	return ret ?: nbytes;
 }
@@ -2659,6 +2727,58 @@ void rdtgroup_kn_unlock(struct kernfs_node *kn)
 	rdtgroup_kn_put(rdtgrp, kn);
 }
 
+/*
+ * Accessing the kn after breaking active protection is safe since the open
+ * of resctrl file holds a kernfs base reference (different from active
+ * protection) on the kn ensuring that it remains accessible even if it was
+ * unlinked. Each kn in turn holds base reference to parent so the kn's
+ * genealogy remains in memory until all base references dropped.
+ */
+static bool is_active_resctrl_node(struct kernfs_node *kn)
+{
+	struct kernfs_node *p;
+	bool match = false;
+
+	guard(rcu)();
+	p = kn;
+	while (p) {
+		if (p == rdtgroup_default.kn) {
+			match = true;
+			break;
+		}
+		p = rcu_dereference(p->__parent);
+	}
+
+	return match;
+}
+
+bool info_kn_lock(struct kernfs_node *kn)
+{
+	kernfs_break_active_protection(kn);
+	cpus_read_lock();
+	mutex_lock(&rdtgroup_mutex);
+
+	/*
+	 * Check both if resctrl is torn down (!rdtgroup_default.kn) and
+	 * if the reader's kernfs_node originates from a dead mount.
+	 */
+	if (!rdtgroup_default.kn || !is_active_resctrl_node(kn)) {
+		mutex_unlock(&rdtgroup_mutex);
+		cpus_read_unlock();
+		kernfs_unbreak_active_protection(kn);
+		return false;
+	}
+
+	return true;
+}
+
+void info_kn_unlock(struct kernfs_node *kn)
+{
+	mutex_unlock(&rdtgroup_mutex);
+	cpus_read_unlock();
+	kernfs_unbreak_active_protection(kn);
+}
+
 static int mkdir_mondata_all(struct kernfs_node *parent_kn,
 			     struct rdtgroup *prgrp,
 			     struct kernfs_node **mon_data_kn);
-- 
2.54.0

[PATCH v7 6/7] x86/resctrl: Ensure domain fully initialized before placed on RCU list

[Reinette Chatre]

A resctrl domain consists of the domain structure self that includes
pointers to dynamically allocated filesystem as well as architecture
specific data. For example, the L3 monitoring domain structure consists
of the architecture specific struct rdt_hw_l3_mon_domain that contains
the dynamically allocated rdt_hw_l3_mon_domain::arch_mbm_states
architectural state and the embedded struct rdt_l3_mon_domain contains
the dynamically allocated rdt_l3_mon_domain::mbm_states resctrl fs state.

The domains are added to and removed from an RCU protected list while
cpus_write_lock() is held so that readers could access domains via
cpus_read_lock() or from an RCU read-side critical section.

A reader accessing a domain via the RCU list expects that the domain and
all its dynamically allocated data is accessible. Only place the domain on
the RCU list when all its dynamically allocated data is ready, similarly
unlink it from RCU list (again with cpus_write_lock() held) before removing
any of its dynamically allocated data.

Calling resctrl_online_mon_domain() before adding the domain to the RCU
list creates the kernfs files that expose the domain's monitoring data to
user space before adding the domain to the RCU list. This is safe because
rdtgroup_mondata_show() acquires cpus_read_lock() before it traverses the
RCU list and will thus block until the domain is added to the RCU list.

There are no readers accessing a domain via RCU list. Ensure safety of
access when such a reader arrives.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Chen Yu <yu.c.chen@intel.com>
---
Changes since V2:
- New patch

Changes since V3:
- Add Tony's Reviewed-by tag.
- Add Chenyu's Reviewed-by tag.
- Grammar fixes in changelog.
- Add snippet to changelog about possible race with rdtgroup_mondata_show().
---
 arch/x86/kernel/cpu/resctrl/core.c      | 18 +++++++-----------
 arch/x86/kernel/cpu/resctrl/intel_aet.c |  5 ++---
 2 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
index 9c01d2562b7a..bca782050198 100644
--- a/arch/x86/kernel/cpu/resctrl/core.c
+++ b/arch/x86/kernel/cpu/resctrl/core.c
@@ -515,14 +515,12 @@ static void domain_add_cpu_ctrl(int cpu, struct rdt_resource *r)
 		return;
 	}
 
-	list_add_tail_rcu(&d->hdr.list, add_pos);
-
 	err = resctrl_online_ctrl_domain(r, d);
 	if (err) {
-		list_del_rcu(&d->hdr.list);
-		synchronize_rcu();
 		ctrl_domain_free(hw_dom);
+		return;
 	}
+	list_add_tail_rcu(&d->hdr.list, add_pos);
 }
 
 static void l3_mon_domain_setup(int cpu, int id, struct rdt_resource *r, struct list_head *add_pos)
@@ -556,14 +554,12 @@ static void l3_mon_domain_setup(int cpu, int id, struct rdt_resource *r, struct
 		return;
 	}
 
-	list_add_tail_rcu(&d->hdr.list, add_pos);
-
 	err = resctrl_online_mon_domain(r, &d->hdr);
 	if (err) {
-		list_del_rcu(&d->hdr.list);
-		synchronize_rcu();
 		l3_mon_domain_free(hw_dom);
+		return;
 	}
+	list_add_tail_rcu(&d->hdr.list, add_pos);
 }
 
 static void domain_add_cpu_mon(int cpu, struct rdt_resource *r)
@@ -642,9 +638,9 @@ static void domain_remove_cpu_ctrl(int cpu, struct rdt_resource *r)
 	d = container_of(hdr, struct rdt_ctrl_domain, hdr);
 	hw_dom = resctrl_to_arch_ctrl_dom(d);
 
-	resctrl_offline_ctrl_domain(r, d);
 	list_del_rcu(&hdr->list);
 	synchronize_rcu();
+	resctrl_offline_ctrl_domain(r, d);
 
 	/*
 	 * rdt_ctrl_domain "d" is going to be freed below, so clear
@@ -689,9 +685,9 @@ static void domain_remove_cpu_mon(int cpu, struct rdt_resource *r)
 
 		d = container_of(hdr, struct rdt_l3_mon_domain, hdr);
 		hw_dom = resctrl_to_arch_mon_dom(d);
-		resctrl_offline_mon_domain(r, hdr);
 		list_del_rcu(&hdr->list);
 		synchronize_rcu();
+		resctrl_offline_mon_domain(r, hdr);
 		l3_mon_domain_free(hw_dom);
 		break;
 	}
@@ -702,9 +698,9 @@ static void domain_remove_cpu_mon(int cpu, struct rdt_resource *r)
 			return;
 
 		pkgd = container_of(hdr, struct rdt_perf_pkg_mon_domain, hdr);
-		resctrl_offline_mon_domain(r, hdr);
 		list_del_rcu(&hdr->list);
 		synchronize_rcu();
+		resctrl_offline_mon_domain(r, hdr);
 		kfree(pkgd);
 		break;
 	}
diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
index 89b8b619d5d5..c22c3cf5167d 100644
--- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
+++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
@@ -398,12 +398,11 @@ void intel_aet_mon_domain_setup(int cpu, int id, struct rdt_resource *r,
 	d->hdr.type = RESCTRL_MON_DOMAIN;
 	d->hdr.rid = RDT_RESOURCE_PERF_PKG;
 	cpumask_set_cpu(cpu, &d->hdr.cpu_mask);
-	list_add_tail_rcu(&d->hdr.list, add_pos);
 
 	err = resctrl_online_mon_domain(r, &d->hdr);
 	if (err) {
-		list_del_rcu(&d->hdr.list);
-		synchronize_rcu();
 		kfree(d);
+		return;
 	}
+	list_add_tail_rcu(&d->hdr.list, add_pos);
 }
-- 
2.54.0

[PATCH v7 7/7] fs/resctrl: Fix UAF from worker threads when domains are removed

[Reinette Chatre]

The mbm_handle_overflow() and cqm_handle_limbo() workers read event
counters and may sleep while doing so. They are scheduled via
delayed_work embedded in struct rdt_l3_mon_domain. Architecture allocates
and frees these domains from CPU hotplug callbacks under cpus_write_lock(),
and the workers acquire cpus_read_lock() to keep the domain alive across
their access.

A use-after-free can occur when a worker is blocked waiting for
cpus_read_lock() while the hotplug core holds cpus_write_lock():
the architecture frees the rdt_l3_mon_domain that contains the worker's
work_struct. When the worker unblocks, the container_of() it performs on
the embedded work pointer dereferences freed memory.

Drop cpus_read_lock() from the workers and instead drain pending and
in-flight work synchronously before the architecture can free the domain.
Since architecture offlines the domain under cpus_write_lock() after it has
been unlinked from the RCU list and a grace period has elapsed, no new work
can be scheduled. The cancel only needs to wait out existing work.
Drop rdtgroup_mutex during CPU offline around cancel_delayed_work_sync()
so that a worker waiting on the mutex can complete before re-pinning the
work on a different CPU.

When offlining a CPU the architecture may iterate over resources in any
order. For example, the MBA control domain may be offlined before or
after a corresponding L3 monitor domain. Ensure that resctrl fs cancels
the workers no matter what order the architecture offlines the domains.

Fixes: 24247aeeabe9 ("x86/intel_rdt/cqm: Improve limbo list processing")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260429184858.36423-1-tony.luck%40intel.com # [1]
Co-developed-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
---
Changes since v2:
- Rewrite changelog
- v2 attempted to solve the issue by using is_percpu_thread() within the
  worker to learn if CPU worker was running on is going offline. A
  Sashiko (https://sashiko.dev/#/patchset/20260515193944.15114-1-tony.luck%40intel.com?part=5)
  pointed out that this would not be able to handle the scenario if one
  of the hotplug handlers following the resctrl offline handlers failed.
- Some other fixes attempted that failed:
  - Switch to accessing domain structure in handler via RCU so that CPU
    hotplug lock no longer needed. Use cancel_delayed_work_sync() with
    mutex dropped to cancel worker. Running worker from RCU read-side
    critical section is a problem since the worker needs to be
    able to sleep (mbm_handle_overflow()->mbm_update()->
		    mbm_update_one_event()->resctrl_arch_mon_ctx_alloc()->
		    might_sleep())
  - Adding a reference count to the domain structure to avoid the worker
    needing to take CPU hotplug lock. This ended up being very complicated
    with the architecture needing new APIs to manage the reference count
    which cannot cleanly integrate into MPAM since it uses a single
    architecture domain structure to contain both the control and monitoring
    domain structures. Managing the references across mount, unmount,
    online, offline, as well as worker self exit resulted in several
    asymmetrical and complicated paths that were error prone. Locking also
    proved to be complicated since architecture would need to initiate
    domain free that will need to call back into resctrl that will take
    rdtgroup_mutex which means that references need to be taken/released
    without locking.

Changes since V3:
- Traverse mon_domains list using list_for_each_entry_rcu( ...,
  lockdep_is_cpus_held()) to document how CPU hotplug lock is required
  to be held (via architecture).
- Add snippet in changelog to motivate canceling work in monitor and
  control domain offline handlers.

Changes since V4:
- Add check for empty domain to workers to avoid reading RMID when
  domain's cpu_mask is empty because x86's resctrl_arch_rmid_read()
  depends on there being CPUs in the domain's cpu_mask.
---
 fs/resctrl/monitor.c  | 60 +++++++++++++++++++++++++++++++++++--------
 fs/resctrl/rdtgroup.c | 52 +++++++++++++++++++++++++++++++++----
 2 files changed, 97 insertions(+), 15 deletions(-)

diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 15e3eeddb6df..7340b1d17f17 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -633,14 +633,22 @@ void mon_event_count(void *info)
 		rr->err = 0;
 }
 
-static struct rdt_ctrl_domain *get_ctrl_domain_from_cpu(int cpu,
-							struct rdt_resource *r)
+/*
+ * Find the software controller's ctrl domain that contains @cpu on resource @r.
+ *
+ * Only called from the mbm_over worker via update_mba_bw() where the returned
+ * domain is kept alive by cancel_delayed_work_sync() in
+ * resctrl_offline_ctrl_domain(). This drains this worker and then waits on
+ * rdtgroup_mutex held here before the architecture can free the ctrl domain.
+ *
+ * Context: Call from RCU read-side critical section.
+ */
+static struct rdt_ctrl_domain *get_sc_ctrl_domain_from_cpu(int cpu,
+							   struct rdt_resource *r)
 {
 	struct rdt_ctrl_domain *d;
 
-	lockdep_assert_cpus_held();
-
-	list_for_each_entry(d, &r->ctrl_domains, hdr.list) {
+	list_for_each_entry_rcu(d, &r->ctrl_domains, hdr.list) {
 		/* Find the domain that contains this CPU */
 		if (cpumask_test_cpu(cpu, &d->hdr.cpu_mask))
 			return d;
@@ -701,7 +709,8 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_l3_mon_domain *dom_m
 	if (WARN_ON_ONCE(!pmbm_data))
 		return;
 
-	dom_mba = get_ctrl_domain_from_cpu(smp_processor_id(), r_mba);
+	guard(rcu)();
+	dom_mba = get_sc_ctrl_domain_from_cpu(smp_processor_id(), r_mba);
 	if (!dom_mba) {
 		pr_warn_once("Failure to get domain for MBA update\n");
 		return;
@@ -804,11 +813,25 @@ void cqm_handle_limbo(struct work_struct *work)
 	unsigned long delay = msecs_to_jiffies(CQM_LIMBOCHECK_INTERVAL);
 	struct rdt_l3_mon_domain *d;
 
-	cpus_read_lock();
+	/*
+	 * Safe to run without CPU hotplug lock. Work is guaranteed to be
+	 * canceled before the domain structure is removed.
+	 */
 	mutex_lock(&rdtgroup_mutex);
 
+	/*
+	 * Ensure the worker is dedicated to a CPU as intended and not
+	 * relocated by workqueue subsystem as part of CPU going offline.
+	 */
+	if (!is_percpu_thread())
+		goto out_unlock;
+
 	d = container_of(work, struct rdt_l3_mon_domain, cqm_limbo.work);
 
+	/* Domain is going offline */
+	if (cpumask_empty(&d->hdr.cpu_mask))
+		goto out_unlock;
+
 	__check_limbo(d, false);
 
 	if (has_busy_rmid(d)) {
@@ -818,8 +841,8 @@ void cqm_handle_limbo(struct work_struct *work)
 					 delay);
 	}
 
+out_unlock:
 	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
 }
 
 /**
@@ -851,7 +874,10 @@ void mbm_handle_overflow(struct work_struct *work)
 	struct list_head *head;
 	struct rdt_resource *r;
 
-	cpus_read_lock();
+	/*
+	 * Safe to run without CPU hotplug lock. Work is guaranteed to be
+	 * canceled before the domain structure is removed.
+	 */
 	mutex_lock(&rdtgroup_mutex);
 
 	/*
@@ -861,9 +887,24 @@ void mbm_handle_overflow(struct work_struct *work)
 	if (!resctrl_mounted || !resctrl_arch_mon_capable())
 		goto out_unlock;
 
+	/*
+	 * Ensure the worker is dedicated to a CPU and not relocated by
+	 * workqueue subsystem as part of CPU going offline since reading
+	 * events depend on smp_processor_id(). After passing this check
+	 * smp_processor_id() is valid for entire duration of this worker
+	 * since it runs with rdtgroup_mutex held and the offline handler needs
+	 * rdtgroup_mutex to offline the CPU being run on here.
+	 */
+	if (!is_percpu_thread())
+		goto out_unlock;
+
 	r = resctrl_arch_get_resource(RDT_RESOURCE_L3);
 	d = container_of(work, struct rdt_l3_mon_domain, mbm_over.work);
 
+	/* Domain is going offline */
+	if (cpumask_empty(&d->hdr.cpu_mask))
+		goto out_unlock;
+
 	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
 		mbm_update(r, d, prgrp);
 
@@ -885,7 +926,6 @@ void mbm_handle_overflow(struct work_struct *work)
 
 out_unlock:
 	mutex_unlock(&rdtgroup_mutex);
-	cpus_read_unlock();
 }
 
 /**
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index 2fd68733166c..30df902ea776 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -4489,6 +4489,29 @@ static void domain_destroy_l3_mon_state(struct rdt_l3_mon_domain *d)
 
 void resctrl_offline_ctrl_domain(struct rdt_resource *r, struct rdt_ctrl_domain *d)
 {
+	/*
+	 * mbm_handle_overflow() may dereference this ctrl domain via
+	 * update_mba_bw()->get_sc_ctrl_domain_from_cpu(). The architecture has
+	 * unlinked the domain from the RCU list and waited a grace period, so
+	 * no new worker iteration can find it; drain any worker that already
+	 * holds a pointer to it before the architecture frees the domain.
+	 *
+	 * Software controller is enabled/disabled on mount/unmount with
+	 * cpus_read_lock() held. Running here with cpus_write_lock() so
+	 * there are no concurrent changes to software controller status.
+	 */
+	if (r->rid == RDT_RESOURCE_MBA && is_mba_sc(r)) {
+		struct rdt_resource *l3 = resctrl_arch_get_resource(RDT_RESOURCE_L3);
+		struct rdt_l3_mon_domain *mon_d;
+
+		list_for_each_entry_rcu(mon_d, &l3->mon_domains, hdr.list, lockdep_is_cpus_held()) {
+			if (mon_d->hdr.id == d->hdr.id) {
+				cancel_delayed_work_sync(&mon_d->mbm_over);
+				break;
+			}
+		}
+	}
+
 	mutex_lock(&rdtgroup_mutex);
 
 	if (supports_mba_mbps() && r->rid == RDT_RESOURCE_MBA)
@@ -4501,6 +4524,24 @@ void resctrl_offline_mon_domain(struct rdt_resource *r, struct rdt_domain_hdr *h
 {
 	struct rdt_l3_mon_domain *d;
 
+	/*
+	 * Called by architecture under CPU hotplug lock as it prepares to remove
+	 * the domain which is guaranteed to be accessible here.
+	 * The domain has been unlinked from the RCU list and a grace period
+	 * has elapsed, so no new worker can be scheduled. Drain any worker that
+	 * is in flight or pending before letting architecture proceed to free
+	 * the domain that has the workers' struct delayed_work embedded.
+	 * Do so before taking rdtgroup_mutex since the workers also acquire it.
+	 */
+	if (r->rid == RDT_RESOURCE_L3 &&
+	    domain_header_is_valid(hdr, RESCTRL_MON_DOMAIN, RDT_RESOURCE_L3)) {
+		d = container_of(hdr, struct rdt_l3_mon_domain, hdr);
+		if (resctrl_is_mbm_enabled())
+			cancel_delayed_work_sync(&d->mbm_over);
+		if (resctrl_is_mon_event_enabled(QOS_L3_OCCUP_EVENT_ID))
+			cancel_delayed_work_sync(&d->cqm_limbo);
+	}
+
 	mutex_lock(&rdtgroup_mutex);
 
 	/*
@@ -4517,8 +4558,6 @@ void resctrl_offline_mon_domain(struct rdt_resource *r, struct rdt_domain_hdr *h
 		goto out_unlock;
 
 	d = container_of(hdr, struct rdt_l3_mon_domain, hdr);
-	if (resctrl_is_mbm_enabled())
-		cancel_delayed_work(&d->mbm_over);
 	if (resctrl_is_mon_event_enabled(QOS_L3_OCCUP_EVENT_ID) && has_busy_rmid(d)) {
 		/*
 		 * When a package is going down, forcefully
@@ -4529,7 +4568,6 @@ void resctrl_offline_mon_domain(struct rdt_resource *r, struct rdt_domain_hdr *h
 		 * package never comes back.
 		 */
 		__check_limbo(d, true);
-		cancel_delayed_work(&d->cqm_limbo);
 	}
 
 	domain_destroy_l3_mon_state(d);
@@ -4710,12 +4748,16 @@ void resctrl_offline_cpu(unsigned int cpu)
 	d = get_mon_domain_from_cpu(cpu, l3);
 	if (d) {
 		if (resctrl_is_mbm_enabled() && cpu == d->mbm_work_cpu) {
-			cancel_delayed_work(&d->mbm_over);
+			mutex_unlock(&rdtgroup_mutex);
+			cancel_delayed_work_sync(&d->mbm_over);
+			mutex_lock(&rdtgroup_mutex);
 			mbm_setup_overflow_handler(d, 0, cpu);
 		}
 		if (resctrl_is_mon_event_enabled(QOS_L3_OCCUP_EVENT_ID) &&
 		    cpu == d->cqm_work_cpu && has_busy_rmid(d)) {
-			cancel_delayed_work(&d->cqm_limbo);
+			mutex_unlock(&rdtgroup_mutex);
+			cancel_delayed_work_sync(&d->cqm_limbo);
+			mutex_lock(&rdtgroup_mutex);
 			cqm_setup_limbo_handler(d, 0, cpu);
 		}
 	}
-- 
2.54.0

Re: [PATCH v7 0/7] x86,fs/resctrl: Fix long-standing issues

[Borislav Petkov]

On Mon, Jul 13, 2026 at 10:39:36AM -0700, Reinette Chatre wrote:
> v6: https://lore.kernel.org/lkml/cover.1783377598.git.reinette.chatre@intel.com/
> v5: https://lore.kernel.org/lkml/cover.1781029125.git.reinette.chatre@intel.com/
> v4: https://lore.kernel.org/lkml/cover.1780456704.git.reinette.chatre@intel.com/
> v3: https://lore.kernel.org/lkml/cover.1779476724.git.reinette.chatre@intel.com/
> v2: https://lore.kernel.org/lkml/20260515193944.15114-1-tony.luck@intel.com/
> v1: https://lore.kernel.org/all/20260508182143.14592-1-tony.luck@intel.com/
> 
> While reviewing the AET series [1] Sashiko reported a deadlock during mount,
> and a use-after-free when an L3 domain is removed during CPU offline. More issues
> were uncovered as fixes were developed and reviewed. While the goal is to
> fix all issues the races surrounding pseudo-locked regions are not yet
> solved and have been removed from this series (last appearance was in V3 of
> this series).
> 
> Applies against v7.2-rc3.

Ack, now that your fixes are upstream, lemme stick those ontop.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Re: [PATCH v7 0/7] x86,fs/resctrl: Fix long-standing issues

[Reinette Chatre]

On 7/13/26 11:29 AM, Borislav Petkov wrote:
> On Mon, Jul 13, 2026 at 10:39:36AM -0700, Reinette Chatre wrote:
>> v6: https://lore.kernel.org/lkml/cover.1783377598.git.reinette.chatre@intel.com/
>> v5: https://lore.kernel.org/lkml/cover.1781029125.git.reinette.chatre@intel.com/
>> v4: https://lore.kernel.org/lkml/cover.1780456704.git.reinette.chatre@intel.com/
>> v3: https://lore.kernel.org/lkml/cover.1779476724.git.reinette.chatre@intel.com/
>> v2: https://lore.kernel.org/lkml/20260515193944.15114-1-tony.luck@intel.com/
>> v1: https://lore.kernel.org/all/20260508182143.14592-1-tony.luck@intel.com/
>>
>> While reviewing the AET series [1] Sashiko reported a deadlock during mount,
>> and a use-after-free when an L3 domain is removed during CPU offline. More issues
>> were uncovered as fixes were developed and reviewed. While the goal is to
>> fix all issues the races surrounding pseudo-locked regions are not yet
>> solved and have been removed from this series (last appearance was in V3 of
>> this series).
>>
>> Applies against v7.2-rc3.
> 
> Ack, now that your fixes are upstream, lemme stick those ontop.
Thank you very much Boris.

Reinette