Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH v2] mm: memcg/slab: wait for !root kmem_cache refcnt killing on root kmem_cache destruction
@ 2019-11-29  2:50 Roman Gushchin
  2019-11-29  8:43 ` Michal Hocko
  0 siblings, 1 reply; 2+ messages in thread
From: Roman Gushchin @ 2019-11-29  2:50 UTC (permalink / raw)
  To: linux-mm, Andrew Morton
  Cc: Michal Hocko, Johannes Weiner, linux-kernel, kernel-team,
	Christian Borntraeger, Shakeel Butt, Roman Gushchin, stable

Christian reported a warning like the following obtained during running some
KVM-related tests on s390:

WARNING: CPU: 8 PID: 208 at lib/percpu-refcount.c:108 percpu_ref_exit+0x50/0x58
Modules linked in: kvm(-) xt_CHECKSUM xt_MASQUERADE bonding xt_tcpudp ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ip6table_na>
CPU: 8 PID: 208 Comm: kworker/8:1 Not tainted 5.2.0+ #66
Hardware name: IBM 2964 NC9 712 (LPAR)
Workqueue: events sysfs_slab_remove_workfn
Krnl PSW : 0704e00180000000 0000001529746850 (percpu_ref_exit+0x50/0x58)
           R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
Krnl GPRS: 00000000ffff8808 0000001529746740 000003f4e30e8e18 0036008100000000
           0000001f00000000 0035008100000000 0000001fb3573ab8 0000000000000000
           0000001fbdb6de00 0000000000000000 0000001529f01328 0000001fb3573b00
           0000001fbb27e000 0000001fbdb69300 000003e009263d00 000003e009263cd0
Krnl Code: 0000001529746842: f0a0000407fe        srp        4(11,%r0),2046,0
           0000001529746848: 47000700            bc         0,1792
          #000000152974684c: a7f40001            brc        15,152974684e
          >0000001529746850: a7f4fff2            brc        15,1529746834
           0000001529746854: 0707                bcr        0,%r7
           0000001529746856: 0707                bcr        0,%r7
           0000001529746858: eb8ff0580024        stmg       %r8,%r15,88(%r15)
           000000152974685e: a738ffff            lhi        %r3,-1
Call Trace:
([<000003e009263d00>] 0x3e009263d00)
 [<00000015293252ea>] slab_kmem_cache_release+0x3a/0x70
 [<0000001529b04882>] kobject_put+0xaa/0xe8
 [<000000152918cf28>] process_one_work+0x1e8/0x428
 [<000000152918d1b0>] worker_thread+0x48/0x460
 [<00000015291942c6>] kthread+0x126/0x160
 [<0000001529b22344>] ret_from_fork+0x28/0x30
 [<0000001529b2234c>] kernel_thread_starter+0x0/0x10
Last Breaking-Event-Address:
 [<000000152974684c>] percpu_ref_exit+0x4c/0x58
---[ end trace b035e7da5788eb09 ]---

The problem occurs because kmem_cache_destroy() is called immediately
after deleting of a memcg, so it races with the memcg kmem_cache
deactivation.

flush_memcg_workqueue() at the beginning of kmem_cache_destroy()
is supposed to guarantee that all deactivation processes are finished,
but failed to do so. It waits for an rcu grace period, after which all
children kmem_caches should be deactivated. During the deactivation
percpu_ref_kill() is called for non root kmem_cache refcounters,
but it requires yet another rcu grace period to finish the transition
to the atomic (dead) state.

So in a rare case when not all children kmem_caches are destroyed
at the moment when the root kmem_cache is about to be gone, we need
to wait another rcu grace period before destroying the root
kmem_cache.

This issue can be triggered only with dynamically created kmem_caches
which are used with memcg accounting. In this case per-memcg child
kmem_caches are created. They are deactivated from the cgroup removing
path. If the destruction of the root kmem_cache is racing with the
removal of the cgroup (both are quite complicated multi-stage
processes), the described issue can occur. The only known way to
trigger it in the real life, is to unload some kernel module which
creates a dedicated kmem_cache, used from different memory cgroups
with GFP_ACCOUNT flag. If the unloading happens immediately after
calling rmdir on the corresponding cgroup, there is some chance to
trigger the issue.

v2: added a note to the commit log, proposed by Michal Hocko

Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Fixes: f0a3a24b532d ("mm: memcg/slab: rework non-root kmem_cache lifecycle management")
Signed-off-by: Roman Gushchin <guro@fb.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Cc: stable@vger.kernel.org
---
 mm/slab_common.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 8afa188f6e20..f0ab6d4ceb4c 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -904,6 +904,18 @@ static void flush_memcg_workqueue(struct kmem_cache *s)
 	 * previous workitems on workqueue are processed.
 	 */
 	flush_workqueue(memcg_kmem_cache_wq);
+
+	/*
+	 * If we're racing with children kmem_cache deactivation, it might
+	 * take another rcu grace period to complete their destruction.
+	 * At this moment the corresponding percpu_ref_kill() call should be
+	 * done, but it might take another rcu grace period to complete
+	 * switching to the atomic mode.
+	 * Please, note that we check without grabbing the slab_mutex. It's safe
+	 * because at this moment the children list can't grow.
+	 */
+	if (!list_empty(&s->memcg_params.children))
+		rcu_barrier();
 }
 #else
 static inline int shutdown_memcg_caches(struct kmem_cache *s)
-- 
2.17.1



^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH v2] mm: memcg/slab: wait for !root kmem_cache refcnt killing on root kmem_cache destruction
  2019-11-29  2:50 [PATCH v2] mm: memcg/slab: wait for !root kmem_cache refcnt killing on root kmem_cache destruction Roman Gushchin
@ 2019-11-29  8:43 ` Michal Hocko
  0 siblings, 0 replies; 2+ messages in thread
From: Michal Hocko @ 2019-11-29  8:43 UTC (permalink / raw)
  To: Roman Gushchin
  Cc: linux-mm, Andrew Morton, Johannes Weiner, linux-kernel,
	kernel-team, Christian Borntraeger, Shakeel Butt, stable

On Thu 28-11-19 18:50:11, Roman Gushchin wrote:
> Christian reported a warning like the following obtained during running some
> KVM-related tests on s390:
> 
> WARNING: CPU: 8 PID: 208 at lib/percpu-refcount.c:108 percpu_ref_exit+0x50/0x58
> Modules linked in: kvm(-) xt_CHECKSUM xt_MASQUERADE bonding xt_tcpudp ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ip6table_na>
> CPU: 8 PID: 208 Comm: kworker/8:1 Not tainted 5.2.0+ #66
> Hardware name: IBM 2964 NC9 712 (LPAR)
> Workqueue: events sysfs_slab_remove_workfn
> Krnl PSW : 0704e00180000000 0000001529746850 (percpu_ref_exit+0x50/0x58)
>            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3
> Krnl GPRS: 00000000ffff8808 0000001529746740 000003f4e30e8e18 0036008100000000
>            0000001f00000000 0035008100000000 0000001fb3573ab8 0000000000000000
>            0000001fbdb6de00 0000000000000000 0000001529f01328 0000001fb3573b00
>            0000001fbb27e000 0000001fbdb69300 000003e009263d00 000003e009263cd0
> Krnl Code: 0000001529746842: f0a0000407fe        srp        4(11,%r0),2046,0
>            0000001529746848: 47000700            bc         0,1792
>           #000000152974684c: a7f40001            brc        15,152974684e
>           >0000001529746850: a7f4fff2            brc        15,1529746834
>            0000001529746854: 0707                bcr        0,%r7
>            0000001529746856: 0707                bcr        0,%r7
>            0000001529746858: eb8ff0580024        stmg       %r8,%r15,88(%r15)
>            000000152974685e: a738ffff            lhi        %r3,-1
> Call Trace:
> ([<000003e009263d00>] 0x3e009263d00)
>  [<00000015293252ea>] slab_kmem_cache_release+0x3a/0x70
>  [<0000001529b04882>] kobject_put+0xaa/0xe8
>  [<000000152918cf28>] process_one_work+0x1e8/0x428
>  [<000000152918d1b0>] worker_thread+0x48/0x460
>  [<00000015291942c6>] kthread+0x126/0x160
>  [<0000001529b22344>] ret_from_fork+0x28/0x30
>  [<0000001529b2234c>] kernel_thread_starter+0x0/0x10
> Last Breaking-Event-Address:
>  [<000000152974684c>] percpu_ref_exit+0x4c/0x58
> ---[ end trace b035e7da5788eb09 ]---
> 
> The problem occurs because kmem_cache_destroy() is called immediately
> after deleting of a memcg, so it races with the memcg kmem_cache
> deactivation.
> 
> flush_memcg_workqueue() at the beginning of kmem_cache_destroy()
> is supposed to guarantee that all deactivation processes are finished,
> but failed to do so. It waits for an rcu grace period, after which all
> children kmem_caches should be deactivated. During the deactivation
> percpu_ref_kill() is called for non root kmem_cache refcounters,
> but it requires yet another rcu grace period to finish the transition
> to the atomic (dead) state.
> 
> So in a rare case when not all children kmem_caches are destroyed
> at the moment when the root kmem_cache is about to be gone, we need
> to wait another rcu grace period before destroying the root
> kmem_cache.
> 
> This issue can be triggered only with dynamically created kmem_caches
> which are used with memcg accounting. In this case per-memcg child
> kmem_caches are created. They are deactivated from the cgroup removing
> path. If the destruction of the root kmem_cache is racing with the
> removal of the cgroup (both are quite complicated multi-stage
> processes), the described issue can occur. The only known way to
> trigger it in the real life, is to unload some kernel module which
> creates a dedicated kmem_cache, used from different memory cgroups
> with GFP_ACCOUNT flag. If the unloading happens immediately after
> calling rmdir on the corresponding cgroup, there is some chance to
> trigger the issue.
> 
> v2: added a note to the commit log, proposed by Michal Hocko
> 
> Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Fixes: f0a3a24b532d ("mm: memcg/slab: rework non-root kmem_cache lifecycle management")
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>
> Cc: stable@vger.kernel.org

Thanks for extending the changelog. This is easier to digest.
Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  mm/slab_common.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 8afa188f6e20..f0ab6d4ceb4c 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -904,6 +904,18 @@ static void flush_memcg_workqueue(struct kmem_cache *s)
>  	 * previous workitems on workqueue are processed.
>  	 */
>  	flush_workqueue(memcg_kmem_cache_wq);
> +
> +	/*
> +	 * If we're racing with children kmem_cache deactivation, it might
> +	 * take another rcu grace period to complete their destruction.
> +	 * At this moment the corresponding percpu_ref_kill() call should be
> +	 * done, but it might take another rcu grace period to complete
> +	 * switching to the atomic mode.
> +	 * Please, note that we check without grabbing the slab_mutex. It's safe
> +	 * because at this moment the children list can't grow.
> +	 */
> +	if (!list_empty(&s->memcg_params.children))
> +		rcu_barrier();
>  }
>  #else
>  static inline int shutdown_memcg_caches(struct kmem_cache *s)
> -- 
> 2.17.1

-- 
Michal Hocko
SUSE Labs


^ permalink raw reply	[flat|nested] 2+ messages in thread

end of thread, back to index

Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-11-29  2:50 [PATCH v2] mm: memcg/slab: wait for !root kmem_cache refcnt killing on root kmem_cache destruction Roman Gushchin
2019-11-29  8:43 ` Michal Hocko

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git