Re: [PATCH 09/18] ipc, shm: make shmem attach/detach wait for mmap_sem killable

[Davidlohr Bueso]

On Mon, 29 Feb 2016, Michal Hocko wrote:

> From: Michal Hocko <mhocko@xxxxxxxx>
>
> shmat and shmdt rely on 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: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

I have no objection to this perse, just one comment below.

Acked-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>

> ---
> ipc/shm.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 331fc1b0b3c7..b8cfa05940d2 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -1200,7 +1200,11 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
> 	if (err)
> 		goto out_fput;
>
> -	down_write(&current->mm->mmap_sem);
> +	if (down_write_killable(&current->mm->mmap_sem)) {
> +		err = -EINVAL;
> +		goto out_fput;
> +	}

This should be EINTR, no?

Thanks,
Davidlohr

> +
> 	if (addr && !(shmflg & SHM_REMAP)) {
> 		err = -EINVAL;
> 		if (addr + size < addr)
> @@ -1271,7 +1275,8 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
> 	if (addr & ~PAGE_MASK)
> 		return retval;
>
> -	down_write(&mm->mmap_sem);
> +	if (down_write_killable(&mm->mmap_sem))
> +		return -EINTR;
>
> 	/*
> 	 * This function tries to be smart and unmap shm segments that
> --
> 2.7.0