From: Qian Cai cai@lca.pw
[ Upstream commit 745e10146c31b1c6ed3326286704ae251b17f663 ]
"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
[akpm@linux-foundation.org: tweak comment] Link: http://lkml.kernel.org/r/20190411032635.10325-1-cai@lca.pw Fixes: d31676dfde25 ("mm/slab: alternative implementation for DEBUG_SLAB_LEAK") Signed-off-by: Qian Cai cai@lca.pw Reviewed-by: Andrew Morton akpm@linux-foundation.org Cc: Vlastimil Babka vbabka@suse.cz Cc: Christoph Lameter cl@linux.com Cc: Pekka Enberg penberg@kernel.org Cc: David Rientjes rientjes@google.com Cc: Joonsoo Kim iamjoonsoo.kim@lge.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- mm/slab.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/mm/slab.c b/mm/slab.c index 018d32496e8d1..46f21e73db2f8 100644 --- a/mm/slab.c +++ b/mm/slab.c @@ -4326,8 +4326,12 @@ static int leaks_show(struct seq_file *m, void *p) * whole processing. */ do { - set_store_user_clean(cachep); drain_cpu_caches(cachep); + /* + * drain_cpu_caches() could make kmemleak_object and + * debug_objects_cache dirty, so reset afterwards. + */ + set_store_user_clean(cachep);
x[1] = 0;