commit 91f4f94ea3f2eabb4cee68149a31e30f84a993dd
author Michal Hocko <mhocko@suse.com> Mon May 23 16:25:51 2016 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> Mon May 23 17:04:14 2016 -0700
tree 1f137113b14e0a66cf24a8c8a32650095f7234d9
parent 7c051267931a9be9c6620cc17b362bc6ee6dedc8

ipc, shm: make shmem attach/detach wait for mmap_sem killable

shmat and shmdt rely on mmap_sem for write.  If the waiting task gets
killed by the oom killer it would block oom_reaper from asynchronous
address space reclaim and reduce the chances of timely OOM resolving.
Wait for the lock in the killable mode and return with EINTR if the task
got killed while waiting.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/shm.c

diff --git a/ipc/shm.c b/ipc/shm.c
index 331fc1b..1328251 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1200,7 +1200,11 @@
 	if (err)
 		goto out_fput;
 
-	down_write(&current->mm->mmap_sem);
+	if (down_write_killable(&current->mm->mmap_sem)) {
+		err = -EINTR;
+		goto out_fput;
+	}
+
 	if (addr && !(shmflg & SHM_REMAP)) {
 		err = -EINVAL;
 		if (addr + size < addr)
@@ -1271,7 +1275,8 @@
 	if (addr & ~PAGE_MASK)
 		return retval;
 
-	down_write(&mm->mmap_sem);
+	if (down_write_killable(&mm->mmap_sem))
+		return -EINTR;
 
 	/*
 	 * This function tries to be smart and unmap shm segments that