The patch titled
Subject: mm,ksm: fix endless looping in allocating memory when ksm enable
has been added to the -mm tree. Its filename is
mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable.patch
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From: zhong jiang <zhongjiang@xxxxxxxxxx>
Subject: mm,ksm: fix endless looping in allocating memory when ksm enable
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>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/ksm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN mm/ksm.c~mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable mm/ksm.c
--- a/mm/ksm.c~mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable
+++ a/mm/ksm.c
@@ -283,7 +283,8 @@ static inline struct rmap_item *alloc_rm
{
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;
_
Patches currently in -mm which might be from zhongjiang@xxxxxxxxxx are
mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable.patch
mm-page_owner-align-with-pageblock_nr-pages.patch
mm-walk-the-zone-in-pageblock_nr_pages-steps.patch
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