* [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 related [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
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