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authorDavid Rientjes <rientjes@google.com>2011-10-31 17:07:18 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-10-31 17:30:45 -0700
commit43362a4977e37db46f86f7e6ab935f0006956632 (patch)
tree5ab7070237ebd3f40d7fcfc0066586422da8310a /mm/swapfile.c
parentc9f01245b6a7d77d17deaa71af10f6aca14fa24e (diff)
downloadlinux-43362a4977e37db46f86f7e6ab935f0006956632.tar.gz
oom: fix race while temporarily setting current's oom_score_adj
test_set_oom_score_adj() was introduced in 72788c385604 ("oom: replace PF_OOM_ORIGIN with toggling oom_score_adj") to temporarily elevate current's oom_score_adj for ksm and swapoff without requiring an additional per-process flag. Using that function to both set oom_score_adj to OOM_SCORE_ADJ_MAX and then reinstate the previous value is racy since it's possible that userspace can set the value to something else itself before the old value is reinstated. That results in userspace setting current's oom_score_adj to a different value and then the kernel immediately setting it back to its previous value without notification. To fix this, a new compare_swap_oom_score_adj() function is introduced with the same semantics as the compare and swap CAS instruction, or CMPXCHG on x86. It is used to reinstate the previous value of oom_score_adj if and only if the present value is the same as the old value. Signed-off-by: David Rientjes <rientjes@google.com> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Ying Han <yinghan@google.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swapfile.c')
-rw-r--r--mm/swapfile.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 17bc224bce6..c9d65400912 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1617,7 +1617,7 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
oom_score_adj = test_set_oom_score_adj(OOM_SCORE_ADJ_MAX);
err = try_to_unuse(type);
- test_set_oom_score_adj(oom_score_adj);
+ compare_swap_oom_score_adj(OOM_SCORE_ADJ_MAX, oom_score_adj);
if (err) {
/*