Re: [PATCH] mm/gup: Let __get_user_pages_locked() return -EINTR for fatal signal

Peter Zijlstra
2020-04-08T17:27:40Z

On Wed, Apr 08, 2020 at 11:59:24AM -0400, Peter Xu wrote:
> From: Hillf Danton <hdanton@sina.com>
>
> __get_user_pages_locked() will return 0 instead of -EINTR after commit
> 4426e945df588 which added extra code to allow gup detect fatal signal
> faster. Restore that behavior.
>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
> Reported-by: syzbot+3be1a33f04dc782e9fd5@syzkaller.appspotmail.com
> Signed-off-by: Hillf Danton <hdanton@sina.com>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>
> PS. Patch verified with syzbot.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> mm/gup.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index afce0bc47e70..6076df8e04a4 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1326,8 +1326,11 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
> * start trying again otherwise it can loop forever.
> */
>
> - if (fatal_signal_pending(current))
> + if (fatal_signal_pending(current)) {
> + if (!pages_done)
> + pages_done = -EINTR;

Why -EINTR here and -ERESTARTSYS at the other site?

> break;
> + }
>
> ret = down_read_killable(&mm->mmap_sem);
> if (ret) {
> --
> 2.24.1
>