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>

diff --git a/ipc/shm.c b/ipc/shm.c
index 331fc1b0b3c7952110f0223d741fc4fa19881d70..13282510bc0da71aa9789ff72ba015bede5c96e7 100644 (file)
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1200,7 +1200,11 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
        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 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
        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