+ mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable.patch added to -mm tree

+ mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable.patch added to -mm tree

[akpm]

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: zhong jiang <zhongjiang@huawei.com>
Subject: mm,ksm: fix endless looping in allocating memory when ksm enable

I hit the following issue when run a OOM case of the LTP and ksm enable.

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

it will lead to a hung task because the exiting task cannot get the mmap
sem for write.  but the root cause is that the ksmd holds it for read
while allocateing memory which just takes ages to complete.  and ksmd will
loop in the following path.

 scan_get_next_rmap_item
          down_read
                get_next_rmap_item
                        alloc_rmap_item   #ksmd will loop permanently.

we fix it by changing the GFP to allow the allocation sometimes fail, and
we're not at all interested in hearing abot that.

Link: http://lkml.kernel.org/r/1474165570-44398-1-git-send-email-zhongjiang@huawei.com
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Suggested-by: Hugh Dickins <hughd@google.com>
Suggested-by: Michal Hocko <mhocko@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@huawei.com 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

+ mmksm-fix-endless-looping-in-allocating-memory-when-ksm-enable.patch added to -mm tree

[akpm]

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

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/SubmitChecklist when testing your code ***

The -mm tree is included into linux-next and is updated
there every 3-4 working days

------------------------------------------------------
From: zhong jiang <zhongjiang@huawei.com>
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@huawei.com
Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Suggested-by: Hugh Dickins <hughd@google.com>
Suggested-by: Michal Hocko <mhocko@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 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@huawei.com 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