From: zhong jiang <zhongjiang@xxxxxxxxxx> 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit 5b398e416e880159fe55eefd93c6588fa072cd66 upstream. I hit the following hung task when runing a OOM LTP test case with 4.1 kernel. Call trace: [<ffffffc000086a88>] __switch_to+0x74/0x8c [<ffffffc000a1bae0>] __schedule+0x23c/0x7bc [<ffffffc000a1c09c>] schedule+0x3c/0x94 [<ffffffc000a1eb84>] rwsem_down_write_failed+0x214/0x350 [<ffffffc000a1e32c>] down_write+0x64/0x80 [<ffffffc00021f794>] __ksm_exit+0x90/0x19c [<ffffffc0000be650>] mmput+0x118/0x11c [<ffffffc0000c3ec4>] do_exit+0x2dc/0xa74 [<ffffffc0000c46f8>] do_group_exit+0x4c/0xe4 [<ffffffc0000d0f34>] get_signal+0x444/0x5e0 [<ffffffc000089fcc>] do_signal+0x1d8/0x450 [<ffffffc00008a35c>] do_notify_resume+0x70/0x78 The oom victim cannot terminate because it needs to take mmap_sem for write while the lock is held by ksmd for read which loops in the page allocator ksm_do_scan scan_get_next_rmap_item down_read get_next_rmap_item alloc_rmap_item #ksmd will loop permanently. There is no way forward because the oom victim cannot release any memory in 4.1 based kernel. Since 4.6 we have the oom reaper which would solve this problem because it would release the memory asynchronously. Nevertheless we can relax alloc_rmap_item requirements and use __GFP_NORETRY because the allocation failure is acceptable as ksm_do_scan would just retry later after the lock got dropped. Such a patch would be also easy to backport to older stable kernels which do not have oom_reaper. While we are at it add GFP_NOWARN so the admin doesn't have to be alarmed by the allocation failure. Link: http://lkml.kernel.org/r/1474165570-44398-1-git-send-email-zhongjiang@xxxxxxxxxx Signed-off-by: zhong jiang <zhongjiang@xxxxxxxxxx> Suggested-by: Hugh Dickins <hughd@xxxxxxxxxx> Suggested-by: Michal Hocko <mhocko@xxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Acked-by: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- mm/ksm.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/ksm.c b/mm/ksm.c index b61ad555184f..9975e218a8b0 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -283,7 +283,8 @@ static inline struct rmap_item *alloc_rmap_item(void) { struct rmap_item *rmap_item; - rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL); + rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL | + __GFP_NORETRY | __GFP_NOWARN); if (rmap_item) ksm_rmap_items++; return rmap_item; -- 2.10.1 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html