Re: [PATCH 11/18] coredump: make coredump_wait wait for mma_sem for write killable

[Vlastimil Babka]

On 02/29/2016 02:26 PM, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> coredump_wait waits for mmap_sem for write currently which can
> prevent oom_reaper to reclaim the oom victims address space
> asynchronously because that requires mmap_sem for read. This might
> happen if the oom victim is multi threaded and some thread(s) is
> holding mmap_sem for read (e.g. page fault) and it is stuck in
> the page allocator while other thread(s) reached coredump_wait
> already.
>
> This patch simply uses down_write_killable and bails out with EINTR
> if the lock got interrupted by the fatal signal. do_coredump will
> return right away and do_group_exit will take care to zap the whole
> thread group.
>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>   fs/coredump.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/coredump.c b/fs/coredump.c
> index 9ea87e9fdccf..6b8aa1629891 100644
> --- a/fs/coredump.c
> +++ b/fs/coredump.c
> @@ -410,7 +410,9 @@ static int coredump_wait(int exit_code, struct core_state *core_state)
>   	core_state->dumper.task = tsk;
>   	core_state->dumper.next = NULL;
>
> -	down_write(&mm->mmap_sem);
> +	if (down_write_killable(&mm->mmap_sem))
> +		return -EINTR;
> +
>   	if (!mm->core_state)
>   		core_waiters = zap_threads(tsk, mm, core_state, exit_code);
>   	up_write(&mm->mmap_sem);