Re: [PATCH] tmpfs: don't interrupt fallocate with EINTR

From: Christian Brauner <brauner@kernel.org>
To: Mikulas Patocka <mpatocka@redhat.com>, Hugh Dickins <hughd@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>,
	 linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] tmpfs: don't interrupt fallocate with EINTR
Date: Tue, 5 Mar 2024 09:42:27 +0100	[thread overview]
Message-ID: <20240305-abgas-tierzucht-1c60219b7839@brauner> (raw)
In-Reply-To: <ef5c3b-fcd0-db5c-8d4-eeae79e62267@redhat.com>

On Mon, Mar 04, 2024 at 07:43:39PM +0100, Mikulas Patocka wrote:
> Hi
> 
> I have a program that sets up a periodic timer with 10ms interval. When
> the program attempts to call fallocate on tmpfs, it goes into an infinite
> loop. fallocate takes longer than 10ms, so it gets interrupted by a
> signal and it returns EINTR. On EINTR, the fallocate call is restarted,
> going into the same loop again.
> 
> fallocate(19, FALLOC_FL_KEEP_SIZE, 0, 206057565) = -1 EINTR (Přerušené volání systému)
> --- SIGALRM {si_signo=SIGALRM, si_code=SI_TIMER, si_timerid=0, si_overrun=0, si_int=0, si_ptr=NULL} ---
> sigreturn({mask=[]})                    = -1 EINTR (Přerušené volání systému)
> fallocate(19, FALLOC_FL_KEEP_SIZE, 0, 206057565) = -1 EINTR (Přerušené volání systému)
> --- SIGALRM {si_signo=SIGALRM, si_code=SI_TIMER, si_timerid=0, si_overrun=0, si_int=0, si_ptr=NULL} ---
> sigreturn({mask=[]})                    = -1 EINTR (Přerušené volání systému)
> fallocate(19, FALLOC_FL_KEEP_SIZE, 0, 206057565) = -1 EINTR (Přerušené volání systému)
> --- SIGALRM {si_signo=SIGALRM, si_code=SI_TIMER, si_timerid=0, si_overrun=0, si_int=0, si_ptr=NULL} ---
> sigreturn({mask=[]})                    = -1 EINTR (Přerušené volání systému)
> fallocate(19, FALLOC_FL_KEEP_SIZE, 0, 206057565) = -1 EINTR (Přerušené volání systému)
> --- SIGALRM {si_signo=SIGALRM, si_code=SI_TIMER, si_timerid=0, si_overrun=0, si_int=0, si_ptr=NULL} ---
> sigreturn({mask=[]})                    = -1 EINTR (Přerušené volání systému)
> 
> Should there be fatal_signal_pending instead of signal_pending in the
> shmem_fallocate loop?
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> 
> ---
>  mm/shmem.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/mm/shmem.c
> ===================================================================
> --- linux-2.6.orig/mm/shmem.c	2024-01-18 19:18:31.000000000 +0100
> +++ linux-2.6/mm/shmem.c	2024-03-04 19:05:25.000000000 +0100
> @@ -3143,7 +3143,7 @@ static long shmem_fallocate(struct file
>  		 * Good, the fallocate(2) manpage permits EINTR: we may have
>  		 * been interrupted because we are using up too much memory.
>  		 */
> -		if (signal_pending(current))
> +		if (fatal_signal_pending(current))

I think that's likely wrong and probably would cause regressions as
there may be users relying on this?