Re: [PATCH 12/18] aio: make aio_setup_ring killable

From: Vlastimil Babka
Date: Fri Mar 11 2016 - 06:57:57 EST

On 02/29/2016 02:26 PM, Michal Hocko wrote:
From: Michal Hocko <mhocko@xxxxxxxx>

aio_setup_ring waits for mmap_sem in writable mode. 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. This will also expedite
the return to the userspace and do_exit.

Cc: Benjamin LaHaise <bcrl@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

The error handling could be changed to labels, but:

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

fs/aio.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/aio.c b/fs/aio.c
index 56bcdf4105f4..1c2e7e2c1b2b 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -520,7 +520,12 @@ static int aio_setup_ring(struct kioctx *ctx)
ctx->mmap_size = nr_pages * PAGE_SIZE;
pr_debug("attempting mmap of %lu bytes\n", ctx->mmap_size);

- down_write(&mm->mmap_sem);
+ if (down_write_killable(&mm->mmap_sem)) {
+ ctx->mmap_size = 0;
+ aio_free_ring(ctx);
+ return -EINTR;
+ }
ctx->mmap_base = do_mmap_pgoff(ctx->aio_ring_file, 0, ctx->mmap_size,
MAP_SHARED, 0, &unused);