@@ -219,7 +219,7 @@ struct obj_cgroup {
struct mem_cgroup *memcg;
atomic_t nr_charged_bytes;
union {
- struct list_head list;
+ struct list_head list; /* protected by objcg_lock */
struct rcu_head rcu;
};
};
@@ -315,7 +315,8 @@ struct mem_cgroup {
#ifdef CONFIG_MEMCG_KMEM
int kmemcg_id;
struct obj_cgroup __rcu *objcg;
- struct list_head objcg_list; /* list of inherited objcgs */
+ /* list of inherited objcgs, protected by objcg_lock */
+ struct list_head objcg_list;
#endif
MEMCG_PADDING(_pad2_);
@@ -254,7 +254,7 @@ struct mem_cgroup *vmpressure_to_memcg(s
}
#ifdef CONFIG_MEMCG_KMEM
-extern spinlock_t css_set_lock;
+static DEFINE_SPINLOCK(objcg_lock);
bool mem_cgroup_kmem_disabled(void)
{
@@ -298,9 +298,9 @@ static void obj_cgroup_release(struct pe
if (nr_pages)
obj_cgroup_uncharge_pages(objcg, nr_pages);
- spin_lock_irqsave(&css_set_lock, flags);
+ spin_lock_irqsave(&objcg_lock, flags);
list_del(&objcg->list);
- spin_unlock_irqrestore(&css_set_lock, flags);
+ spin_unlock_irqrestore(&objcg_lock, flags);
percpu_ref_exit(ref);
kfree_rcu(objcg, rcu);
@@ -332,7 +332,7 @@ static void memcg_reparent_objcgs(struct
objcg = rcu_replace_pointer(memcg->objcg, NULL, true);
- spin_lock_irq(&css_set_lock);
+ spin_lock_irq(&objcg_lock);
/* 1) Ready to reparent active objcg. */
list_add(&objcg->list, &memcg->objcg_list);
@@ -342,7 +342,7 @@ static void memcg_reparent_objcgs(struct
/* 3) Move already reparented objcgs to the parent's list */
list_splice(&memcg->objcg_list, &parent->objcg_list);
- spin_unlock_irq(&css_set_lock);
+ spin_unlock_irq(&objcg_lock);
percpu_ref_kill(&objcg->refcnt);
}
The patch titled Subject: mm: memcg: synchronize objcg lists with a dedicated spinlock has been added to the -mm tree. Its filename is mm-memcg-synchronize-objcg-lists-with-a-dedicated-spinlock.patch This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-memcg-synchronize-objcg-lists-with-a-dedicated-spinlock.patch and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-memcg-synchronize-objcg-lists-with-a-dedicated-spinlock.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Roman Gushchin <guro@fb.com> Subject: mm: memcg: synchronize objcg lists with a dedicated spinlock Alexander reported a circular lock dependency revealed by the mmap1 ltp test: LOCKDEP_CIRCULAR (suite: ltp, case: mtest06 (mmap1)) WARNING: possible circular locking dependency detected 5.17.0-20220113.rc0.git0.f2211f194038.300.fc35.s390x+debug #1 Not tainted ------------------------------------------------------ mmap1/202299 is trying to acquire lock: 00000001892c0188 (css_set_lock){..-.}-{2:2}, at: obj_cgroup_release+0x4a/0xe0 but task is already holding lock: 00000000ca3b3818 (&sighand->siglock){-.-.}-{2:2}, at: force_sig_info_to_task+0x38/0x180 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&sighand->siglock){-.-.}-{2:2}: __lock_acquire+0x604/0xbd8 lock_acquire.part.0+0xe2/0x238 lock_acquire+0xb0/0x200 _raw_spin_lock_irqsave+0x6a/0xd8 __lock_task_sighand+0x90/0x190 cgroup_freeze_task+0x2e/0x90 cgroup_migrate_execute+0x11c/0x608 cgroup_update_dfl_csses+0x246/0x270 cgroup_subtree_control_write+0x238/0x518 kernfs_fop_write_iter+0x13e/0x1e0 new_sync_write+0x100/0x190 vfs_write+0x22c/0x2d8 ksys_write+0x6c/0xf8 __do_syscall+0x1da/0x208 system_call+0x82/0xb0 -> #0 (css_set_lock){..-.}-{2:2}: check_prev_add+0xe0/0xed8 validate_chain+0x736/0xb20 __lock_acquire+0x604/0xbd8 lock_acquire.part.0+0xe2/0x238 lock_acquire+0xb0/0x200 _raw_spin_lock_irqsave+0x6a/0xd8 obj_cgroup_release+0x4a/0xe0 percpu_ref_put_many.constprop.0+0x150/0x168 drain_obj_stock+0x94/0xe8 refill_obj_stock+0x94/0x278 obj_cgroup_charge+0x164/0x1d8 kmem_cache_alloc+0xac/0x528 __sigqueue_alloc+0x150/0x308 __send_signal+0x260/0x550 send_signal+0x7e/0x348 force_sig_info_to_task+0x104/0x180 force_sig_fault+0x48/0x58 __do_pgm_check+0x120/0x1f0 pgm_check_handler+0x11e/0x180 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&sighand->siglock); lock(css_set_lock); lock(&sighand->siglock); lock(css_set_lock); *** DEADLOCK *** 2 locks held by mmap1/202299: #0: 00000000ca3b3818 (&sighand->siglock){-.-.}-{2:2}, at: force_sig_info_to_task+0x38/0x180 #1: 00000001892ad560 (rcu_read_lock){....}-{1:2}, at: percpu_ref_put_many.constprop.0+0x0/0x168 stack backtrace: CPU: 15 PID: 202299 Comm: mmap1 Not tainted 5.17.0-20220113.rc0.git0.f2211f194038.300.fc35.s390x+debug #1 Hardware name: IBM 3906 M04 704 (LPAR) Call Trace: [<00000001888aacfe>] dump_stack_lvl+0x76/0x98 [<0000000187c6d7be>] check_noncircular+0x136/0x158 [<0000000187c6e888>] check_prev_add+0xe0/0xed8 [<0000000187c6fdb6>] validate_chain+0x736/0xb20 [<0000000187c71e54>] __lock_acquire+0x604/0xbd8 [<0000000187c7301a>] lock_acquire.part.0+0xe2/0x238 [<0000000187c73220>] lock_acquire+0xb0/0x200 [<00000001888bf9aa>] _raw_spin_lock_irqsave+0x6a/0xd8 [<0000000187ef6862>] obj_cgroup_release+0x4a/0xe0 [<0000000187ef6498>] percpu_ref_put_many.constprop.0+0x150/0x168 [<0000000187ef9674>] drain_obj_stock+0x94/0xe8 [<0000000187efa464>] refill_obj_stock+0x94/0x278 [<0000000187eff55c>] obj_cgroup_charge+0x164/0x1d8 [<0000000187ed8aa4>] kmem_cache_alloc+0xac/0x528 [<0000000187bf2eb8>] __sigqueue_alloc+0x150/0x308 [<0000000187bf4210>] __send_signal+0x260/0x550 [<0000000187bf5f06>] send_signal+0x7e/0x348 [<0000000187bf7274>] force_sig_info_to_task+0x104/0x180 [<0000000187bf7758>] force_sig_fault+0x48/0x58 [<00000001888ae160>] __do_pgm_check+0x120/0x1f0 [<00000001888c0cde>] pgm_check_handler+0x11e/0x180 INFO: lockdep is turned off. In this example a slab allocation from __send_signal() caused a refilling and draining of a percpu objcg stock, resulted in a releasing of another non-related objcg. Objcg release path requires taking the css_set_lock, which is used to synchronize objcg lists. This can create a circular dependency with the sighandler lock, which is taken with the locked css_set_lock by the freezer code (to freeze a task). In general it seems that using css_set_lock to synchronize objcg lists makes any slab allocations and deallocation with the locked css_set_lock and any intervened locks risky. To fix the problem and make the code more robust let's stop using css_set_lock to synchronize objcg lists and use a new dedicated spinlock instead. Link: https://lkml.kernel.org/r/Yfm1IHmoGdyUR81T@carbon.dhcp.thefacebook.com Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") Signed-off-by: Roman Gushchin <guro@fb.com> Reported-by: Alexander Egorenkov <egorenar@linux.ibm.com> Tested-by: Alexander Egorenkov <egorenar@linux.ibm.com> Reviewed-by: Waiman Long <longman@redhat.com> Acked-by: Tejun Heo <tj@kernel.org> Reviewed-by: Shakeel Butt <shakeelb@google.com> Reviewed-by: Jeremy Linton <jeremy.linton@arm.com> Tested-by: Jeremy Linton <jeremy.linton@arm.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- include/linux/memcontrol.h | 5 +++-- mm/memcontrol.c | 10 +++++----- 2 files changed, 8 insertions(+), 7 deletions(-)