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authorRoman Gushchin <guro@fb.com>2019-12-04 16:49:46 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-12-04 19:44:11 -0800
commita264df74df38855096393447f1b8f386069a94b9 (patch)
tree528225945462bacd7736438c3cc694a1bf587115 /mm/slab_common.c
parent2e7d31704c7fe9141b0b27ec1ece254d9993fe2d (diff)
mm: memcg/slab: wait for !root kmem_cache refcnt killing on root kmem_cache destruction
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. Link: http://lkml.kernel.org/r/20191129025011.3076017-1-guro@fb.com Fixes: f0a3a24b532d ("mm: memcg/slab: rework non-root kmem_cache lifecycle management") Signed-off-by: Roman Gushchin <guro@fb.com> Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> Tested-by: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: Shakeel Butt <shakeelb@google.com> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/slab_common.c')
-rw-r--r--mm/slab_common.c12
1 files changed, 12 insertions, 0 deletions
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)