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Date: Wed, 2 Feb 2022 09:58:15 -0600
From: Jeremy Linton <jeremy.linton@....com>
To: Roman Gushchin <guro@...com>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
Alexander Egorenkov <egorenar@...ux.ibm.com>,
Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>,
Shakeel Butt <shakeelb@...gle.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH RESEND] mm: memcg: synchronize objcg lists with a
dedicated spinlock
On 2/1/22 16:33, Roman Gushchin wrote:
> 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.
>
> Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
> Signed-off-by: Roman Gushchin <guro@...com>
> Reported-by: Alexander Egorenkov <egorenar@...ux.ibm.com>
> Tested-by: Alexander Egorenkov <egorenar@...ux.ibm.com>
> Reviewed-by: Waiman Long <longman@...hat.com>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Shakeel Butt <shakeelb@...gle.com>
> Cc: Jeremy Linton <jeremy.linton@....com>
> Cc: cgroups@...r.kernel.org
> ---
> include/linux/memcontrol.h | 5 +++--
> mm/memcontrol.c | 10 +++++-----
> 2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index b72d75141e12..0abbd685703b 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -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_);
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 09d342c7cbd0..36e9f38c919d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -254,7 +254,7 @@ struct mem_cgroup *vmpressure_to_memcg(struct vmpressure *vmpr)
> }
>
> #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 percpu_ref *ref)
> 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 mem_cgroup *memcg,
>
> 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 mem_cgroup *memcg,
> /* 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);
> }
>
Thanks for taking care of this. Since it looks the same as my patch
aside from the fact that I also defensivly converted the list_del to a
list_del_rcu.
Reviewed-by: Jeremy Linton <jeremy.linton@....com>
and
Tested-by: Jeremy Linton <jeremy.linton@....com>
Thanks again,
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