Re: [PATCH] mm, fork: make dup_mmap wait for mmap_sem for write killable

[Vlastimil Babka]

On 02/29/2016 07:07 PM, Michal Hocko wrote:
> 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>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
>   kernel/fork.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index d277e83ed3e0..139968026b76 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: