[PATCH 08/18] mm, fork: make dup_mmap wait for mmap_sem for write killable

[Michal Hocko]

From: Michal Hocko <mhocko@xxxxxxxx>

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.

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 kernel/fork.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 4bb0a7a0fbe0..bb29839a7e1b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -413,7 +413,10 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 	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);
 	/*
@@ -525,6 +528,7 @@ static int dup_mmap(struct mm_struct *mm, struct mm_struct *oldmm)
 	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:
-- 
2.8.0.rc3