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From: "Eric W. Biederman" <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Olivier Langlois <[email protected]>,
	Pavel Begunkov <[email protected]>,
	[email protected], [email protected],
	[email protected],
	Alexander Viro <[email protected]>,
	Oleg Nesterov <[email protected]>,
	Linus Torvalds <[email protected]>
Subject: [PATCH 2/2] coredump: Allow coredumps to pipes to work with io_uring
Date: Wed, 20 Jul 2022 11:51:27 -0500	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]> (Eric W. Biederman's message of "Wed, 20 Jul 2022 11:49:31 -0500")


Now that io_uring like everything else stops for coredumps in
get_signal the code can once again allow any interruptible
condition after coredump_wait to interrupt the coredump.

Clear TIF_NOTIFY_SIGNAL after coredump_wait, to guarantee that
anything that sets TIF_NOTIFY_SIGNAL before coredump_wait completed
won't cause the coredumps to interrupted.

With all of the other threads in the process stopped io_uring doesn't
call task_work_add on the thread running do_coredump.  Combined with
the clearing of TIF_NOTIFY_SIGNAL this allows processes that use
io_uring to coredump through pipes.

Restore dump_interrupted to be a simple call to signal_pending
effectively reverting commit 06af8679449d ("coredump: Limit what can
interrupt coredumps").  At this point only SIGKILL delivered to the
coredumping thread should be able to cause signal_pending to return
true.

A nice followup would be to find a reliable race free way to modify
task_work_add and probably set_notify_signal to skip setting
TIF_NOTIFY_SIGNAL once it is clear a task will no longer process
signals and other interruptible conditions.  That would allow
TIF_NOTIFY_SIGNAL to be cleared where TIF_SIGPENDING is cleared in
coredump_zap_process.

To be as certain as possible that this works, I tested this with
commit 1d5f5ea7cb7d ("io-wq: remove worker to owner tw dependency")
reverted.  Which means that not only is TIF_NOTIFY_SIGNAL prevented
from stopping coredumps to pipes, the sequence of stopping threads to
participate in the coredump avoids deadlocks that were possible
previously.

Signed-off-by: "Eric W. Biederman" <[email protected]>
---
 fs/coredump.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/coredump.c b/fs/coredump.c
index 67dda77c500f..c06594f56cbb 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -476,7 +476,7 @@ static bool dump_interrupted(void)
 	 * but then we need to teach dump_write() to restart and clear
 	 * TIF_SIGPENDING.
 	 */
-	return fatal_signal_pending(current) || freezing(current);
+	return signal_pending(current);
 }
 
 static void wait_for_dump_helpers(struct file *file)
@@ -589,6 +589,9 @@ void do_coredump(const kernel_siginfo_t *siginfo)
 
 	old_cred = override_creds(cred);
 
+	/* Don't break out of interruptible sleeps */
+	clear_notify_signal();
+
 	ispipe = format_corename(&cn, &cprm, &argv, &argc);
 
 	if (ispipe) {
-- 
2.35.3


  parent reply	other threads:[~2022-07-20 16:51 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <[email protected]>
     [not found] ` <[email protected]>
     [not found]   ` <87h7i694ij.fsf_-_@disp2133>
2021-06-09 20:33     ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Linus Torvalds
2021-06-09 20:48       ` Eric W. Biederman
2021-06-09 20:52         ` Linus Torvalds
2021-06-09 21:02       ` Olivier Langlois
2021-06-09 21:05         ` Eric W. Biederman
2021-06-09 21:26           ` Olivier Langlois
2021-06-09 21:56             ` Olivier Langlois
2021-06-10 14:26             ` Eric W. Biederman
2021-06-10 15:17               ` Olivier Langlois
2021-06-10 18:58               ` [CFT}[PATCH] coredump: Limit what can interrupt coredumps Eric W. Biederman
2021-06-10 19:10                 ` Linus Torvalds
2021-06-10 19:18                   ` Eric W. Biederman
2021-06-10 19:50                     ` Linus Torvalds
2021-06-10 20:11                       ` [PATCH] " Eric W. Biederman
2021-06-10 21:04                         ` Linus Torvalds
2021-06-12 14:36                         ` Olivier Langlois
2021-06-12 16:26                           ` Jens Axboe
2021-06-14 14:10                         ` Oleg Nesterov
2021-06-14 16:37                           ` Eric W. Biederman
2021-06-14 16:59                             ` Oleg Nesterov
2021-06-15 22:08                           ` Eric W. Biederman
2021-06-16 19:23                             ` Olivier Langlois
2021-06-16 20:00                               ` Eric W. Biederman
2021-06-18 20:05                                 ` Olivier Langlois
2021-08-05 13:06                             ` Olivier Langlois
2021-08-10 21:48                               ` Tony Battersby
2021-08-11 20:47                                 ` Olivier Langlois
2021-08-12  1:55                                 ` Jens Axboe
2021-08-12 13:53                                   ` Tony Battersby
2021-08-15 20:42                                   ` Olivier Langlois
2021-08-16 13:02                                     ` Pavel Begunkov
2021-08-16 13:06                                       ` Pavel Begunkov
2021-08-17 18:15                                     ` Jens Axboe
2021-08-17 18:24                                       ` Jens Axboe
2021-08-17 19:29                                         ` Tony Battersby
2021-08-17 19:59                                           ` Jens Axboe
2021-08-17 21:28                                             ` Jens Axboe
2021-08-17 21:39                                               ` Tony Battersby
2021-08-17 22:05                                                 ` Jens Axboe
2021-08-18 14:37                                                   ` Tony Battersby
2021-08-18 14:46                                                     ` Jens Axboe
2021-08-18  2:57                                               ` Jens Axboe
2021-08-18  2:58                                                 ` Jens Axboe
2021-08-21 10:08                                                 ` Olivier Langlois
2021-08-21 16:47                                                   ` Olivier Langlois
2021-08-21 16:51                                                     ` Jens Axboe
2021-08-21 17:21                                                       ` Olivier Langlois
2021-08-21  9:52                                         ` Olivier Langlois
2021-08-21  9:48                                       ` Olivier Langlois
2021-10-22 14:13     ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Pavel Begunkov
2021-12-24  1:34       ` Olivier Langlois
2021-12-24 10:37         ` Pavel Begunkov
2021-12-24 19:52           ` Eric W. Biederman
2021-12-28 11:24             ` Pavel Begunkov
2022-03-14 23:58               ` Eric W. Biederman
     [not found]                 ` <[email protected]>
2022-06-01  3:15                   ` Jens Axboe
2022-07-20 16:49                     ` [PATCH 0/2] coredump: Allow io_uring using apps to dump to pipes Eric W. Biederman
2022-07-20 16:50                       ` [PATCH 1/2] signal: Move stopping for the coredump from do_exit into get_signal Eric W. Biederman
2022-07-20 16:51                       ` Eric W. Biederman [this message]
2022-08-22 21:16                         ` [PATCH 2/2] coredump: Allow coredumps to pipes to work with io_uring Olivier Langlois
2022-08-23  3:35                           ` Olivier Langlois
2022-08-23 18:22                             ` Eric W. Biederman
2022-08-23 18:27                               ` Jens Axboe
2022-08-24 15:11                                 ` Eric W. Biederman
2022-08-24 15:51                                   ` Jens Axboe
2022-01-05 19:39           ` [RFC] coredump: Do not interrupt dump for TIF_NOTIFY_SIGNAL Olivier Langlois

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