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b=qyLBjWoAup0XscsIlT6rAQ3hdK8dnGb0Eg6jcwxbEMpIhYcnB+FWRlg+QA5FngRk1 XgbcGLq2xOId86W7ZB9dAxS7NRG9HpS9ifdSU5fVDf0AVdXYOkISz0Vc3sDl3gmXbx 7/PvY58+RSiC2OVPA9YTCgo/XuFZ5oY1MsgqBvBAtNzGD8mYEJX1fNARfxoEvBcyRz 04nV35lVFwxCOuQHMFNJuGEAb4rfMcpmErGWevDX4LRTFMQjAVqrsfpjvmRixgXzaE 94LIARFNvZw3s523MRHE/VM2eKVLhIWsDiN0mClKVrRVyJQJuPNQDGLzN+ccRU0/p3 1VNh+sjOJw+cw== Date: Thu, 7 Mar 2024 11:47:01 +0100 From: Christian Brauner To: Mikulas Patocka Cc: Hugh Dickins , Alexander Viro , Jan Kara , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] tmpfs: don't interrupt fallocate with EINTR Message-ID: <20240307-entkriminalisierung-wankt-1187288fbb27@brauner> References: <20240305-abgas-tierzucht-1c60219b7839@brauner> <84acfa88-816f-50d7-50a2-92ea7a7db42@redhat.com> <20240305-zugunsten-busbahnhof-6dc705d80152@brauner> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Stat-Signature: 4knfp5r54hmmyiuppx1smopkeg4akxxa X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4F6154000F X-Rspam-User: X-HE-Tag: 1709808429-950389 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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.