linux-kernel - [PATCH 4.7 005/141] mm,ksm: fix endless looping in allocating memory when ksm enable

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20161006074448.852982677@linuxfoundation.org>
Date:   Thu,  6 Oct 2016 10:27:21 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, zhong jiang <zhongjiang@...wei.com>,
        Hugh Dickins <hughd@...gle.com>, Michal Hocko <mhocko@...e.cz>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.7 005/141] mm,ksm: fix endless looping in allocating memory when ksm enable

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: zhong jiang <zhongjiang@...wei.com>

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@huawei.com
Signed-off-by: zhong jiang <zhongjiang@...wei.com>
Suggested-by: Hugh Dickins <hughd@...gle.com>
Suggested-by: Michal Hocko <mhocko@...e.cz>
Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/ksm.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/ksm.c
+++ b/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;