The patch titled
Subject: mm/slab.c: fix an infinite loop in leaks_show()
has been added to the -mm tree. Its filename is
slab-fix-an-infinite-loop-in-leaks_show.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/slab-fix-an-infinite-loop-in-leaks_show.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/slab-fix-an-infinite-loop-in-leaks_show.patch
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------------------------------------------------------
From: Qian Cai <cai@xxxxxx>
Subject: mm/slab.c: fix an infinite loop in leaks_show()
"cat /proc/slab_allocators" could hang forever on SMP machines with
kmemleak or object debugging enabled due to other CPUs running do_drain()
will keep making kmemleak_object or debug_objects_cache dirty and unable
to escape the first loop in leaks_show(),
do {
set_store_user_clean(cachep);
drain_cpu_caches(cachep);
...
} while (!is_store_user_clean(cachep));
For example,
do_drain
slabs_destroy
slab_destroy
kmem_cache_free
__cache_free
___cache_free
kmemleak_free_recursive
delete_object_full
__delete_object
put_object
free_object_rcu
kmem_cache_free
cache_free_debugcheck --> dirty kmemleak_object
One approach is to check cachep->name and skip both kmemleak_object and
debug_objects_cache in leaks_show(). The other is to set store_user_clean
after drain_cpu_caches() which leaves a small window between
drain_cpu_caches() and set_store_user_clean() where per-CPU caches could
be dirty again lead to slightly wrong information has been stored but
could also speed up things significantly which sounds like a good
compromise. For example,
# cat /proc/slab_allocators
0m42.778s # 1st approach
0m0.737s # 2nd approach
Link: http://lkml.kernel.org/r/20190411032635.10325-1-cai@xxxxxx
Fixes: d31676dfde25 ("mm/slab: alternative implementation for DEBUG_SLAB_LEAK")
Signed-off-by: Qian Cai <cai@xxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/slab.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/mm/slab.c~slab-fix-an-infinite-loop-in-leaks_show
+++ a/mm/slab.c
@@ -4327,8 +4327,12 @@ static int leaks_show(struct seq_file *m
* whole processing.
*/
do {
- set_store_user_clean(cachep);
drain_cpu_caches(cachep);
+ /*
+ * drain_cpu_caches() could always make kmemleak_object and
+ * debug_objects_cache dirty, so reset afterwards.
+ */
+ set_store_user_clean(cachep);
x[1] = 0;
_
Patches currently in -mm which might be from cai@xxxxxx are
slab-store-tagged-freelist-for-off-slab-slabmgmt.patch
mm-hotplug-treat-cma-pages-as-unmovable.patch
mm-hotplug-treat-cma-pages-as-unmovable-v4.patch
slab-fix-an-infinite-loop-in-leaks_show.patch
mm-compaction-fix-an-undefined-behaviour.patch
initramfs-cleanup-populate_rootfs-fix.patch
