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

[Vlastimil Babka]

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,
>   				       PROT_READ | PROT_WRITE,
>   				       MAP_SHARED, 0, &unused);