mm, fork: make dup_mmap wait for mmap_sem for write killable

dup_mmap needs to lock current's mm 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: Vlastimil Babka <vbabka@suse.cz>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/fork.c

diff --git a/kernel/fork.c b/kernel/fork.c
index e67d7b7..47887bb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -414,7 +414,10 @@
 	unsigned long charge;
 
 	uprobe_start_dup_mmap();
-	down_write(&oldmm->mmap_sem);
+	if (down_write_killable(&oldmm->mmap_sem)) {
+		retval = -EINTR;
+		goto fail_uprobe_end;
+	}
 	flush_cache_dup_mm(oldmm);
 	uprobe_dup_mmap(oldmm, mm);
 	/*
@@ -526,6 +529,7 @@
 	up_write(&mm->mmap_sem);
 	flush_tlb_mm(oldmm);
 	up_write(&oldmm->mmap_sem);
+fail_uprobe_end:
 	uprobe_end_dup_mmap();
 	return retval;
 fail_nomem_anon_vma_fork: