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

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Date:   Wed, 8 Apr 2020 19:27:23 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hillf Danton <hdanton@...a.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        syzbot+3be1a33f04dc782e9fd5@...kaller.appspotmail.com,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm/gup: Let __get_user_pages_locked() return -EINTR for
 fatal signal

On Wed, Apr 08, 2020 at 11:59:24AM -0400, Peter Xu wrote:
> From: Hillf Danton <hdanton@...a.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@...ux-foundation.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
> Reported-by: syzbot+3be1a33f04dc782e9fd5@...kaller.appspotmail.com
> Signed-off-by: Hillf Danton <hdanton@...a.com>
> Acked-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
> 
> PS. Patch verified with syzbot.
> 
> Signed-off-by: Peter Xu <peterx@...hat.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
>