On Tue, Mar 05, 2024 at 03:03:53PM +0100, Mikulas Patocka wrote: > > > On Tue, 5 Mar 2024, Christian Brauner wrote: > > > On Tue, Mar 05, 2024 at 10:34:26AM +0100, Mikulas Patocka wrote: > > > > > > > > > On Tue, 5 Mar 2024, Christian Brauner wrote: > > > > > > > On Mon, Mar 04, 2024 at 07:43:39PM +0100, Mikulas Patocka wrote: > > > > > > > > > > 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? > > > > > > ext4 fallocate doesn't return -EINTR. So, userspace code can't rely on it. > > > > I'm confused what does this have to do with ext4 since this is about > > tmpfs. > > You said that applications may rely on -EINTR and I said they don't > because ext4 doesn't return -EINTR. > > > Also note, that fallocate(2) documents EINTR as a valid return > > value. And fwiw, the manpage also states that "EINTR A signal was > > caught during execution; see signal(7)." not a "fatal signal". > > Yes, but how should the userspace use the fallocate call reliably? Block > all the signals around the call to fallocate? What to do if I use some > library that calls fallocate and retries on EINTR? > > > Aside from that. If a user sends SIGUSR1 then with the code as it is now > > that fallocate call will be interrupted. With your change that SIGUSR1 > > won't do anything anymore. Instead userspace would need to send SIGKILL. > > So userspace that uses SIGUSR1 will suddenly hang. > > It will survive one SIGUSR, but it hangs if the signal is being sent at a > periodic interval. > > A quick search shows that people are already adding loops when fallocate > returns EINTR. All these loops will livelock when a signal is repeatedly > being delivered: > https://forge.chapril.org/hardcoresushi/libgocryptfs/commit/8518d6d7bde33fdc7ef5bcb7c3c7709404392ad8?style=unified&whitespace= > https://postgrespro.com/media/maillist-attaches/pgsql-hackers/2022/07/1/20220701154105.jjfutmngoedgiad3@alvherre.pgsql/v2-0001-retry-ftruncate.patch > https://lists.nongnu.org/archive/html/qemu-devel/2015-02/msg01116.html > > Here, Postgres developers hit the same problem with retrying (they have > 5ms timer): > https://www.postgresql.org/message-id/CA%2BhUKGKS2Radu-1Ewhe1-LEj19C-3XAQ7wnkQMb4e9E9q9ZXSg%40mail.gmail.com All fair points.
