FAILED: patch "[PATCH] coredump: prevent TIF_NOTIFY_SIGNAL from interrupting" failed to apply to 6.12-stable tree

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x a58d647acfdc62561f3570d114025b3bf38ae41b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026102818-graded-prancing-5aef@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a58d647acfdc62561f3570d114025b3bf38ae41b Mon Sep 17 00:00:00 2001
From: Christian Brauner <[email protected]>
Date: Mon, 24 Aug 2026 14:08:17 +0200
Subject: [PATCH] coredump: prevent TIF_NOTIFY_SIGNAL from interrupting
coredumps

TIF_NOTIFY_SIGNAL is used to kick a task in uninterruptible sleep to return to userspace and run task work and then go back to sleep. This mechanism works well but breaks coredumps. dump_interrupted() only allows fatal signals to interrupt a coredump and the whole regular write path going to actual filesystems is impervious to TIF_NOTIFY_SIGNAL as well.

However, both the usermodehelper pipe and the coredump socket will bail early on TIF_NOTIFY_SIGNAL. This affects the following codepaths:

- coredump_sock_recv() -> unix_stream_read_generic()
The request/ack handshake is abandoned before any coredump data is sent.

- anon_pipe_write() returning -ERESTARTSYS Once the pipe is full this truncates the coredump.

- unix_stream_sendmsg() returning -ERESTARTSYS Once the send buffer is full this truncates the coredump.

- coredump_sock_wait() -> __kernel_read()
This reports a failure that didn't happen.

- wait_for_dump_helpers() -> wait_event_interruptible() This stops waiting for the coredump helpers.

Such truncation is entirely invisible to userspace and all uapi bits still indicate that a successful coredump happened. A crashing process with a bunch of file backed mappings and io_uring thrown in loses most of the coredump data. If the NT_FILE note goes past PAGE_SIZE mappings it's gonzo.

TIF_NOTIFY_SIGNAL is sent by io_uring for the common case. And it uses poll without sleeping so a completion callback runs task_work_add() from interrupt context against the task that submitted the request. This is the task that is running the coredump. Since that task hasn't set work_exited (it hasn't exited yet after all) TIF_NOTIFY_SIGNAL keeps reappearing.

A coredumping task doesn't return to userspace. The task work is run at exit. So interrupting it doesn't buy anything and just loses the coredump which is quite valuable.

Note that this isn't specific to io_uring. There's also klp_send_signals(), bpf_task_work_schedule_signal(), landlock's tsync and then technically, kthread_stop() and the printk kunit test set the bit raw.

index ac3cd74808c6..7c0f276c3e0d 100644
@@ -1191,6 +1191,8 @@ void vfs_coredump(const kernel_siginfo_t *siginfo)
 	if (coredump_wait(siginfo->si_signo, &core_state) < 0)
 		return;
 
+	/* Task work must not cut the dump short, see signal_pending(). */
+	guard(no_notify_signal)();
 	scoped_with_creds(cred)
 		do_coredump(&cn, &cprm, &argv, &argc, binfmt);
 	coredump_cleanup(&cn, &cprm);

From: Christian Brauner <[email protected]>

[ Upstream commit a58d647acfdc62561f3570d114025b3bf38ae41b ]

TIF_NOTIFY_SIGNAL is used to kick a task in uninterruptible sleep to return to userspace and run task work and then go back to sleep. This mechanism works well but breaks coredumps. dump_interrupted() only allows fatal signals to interrupt a coredump and the whole regular write path going to actual filesystems is impervious to TIF_NOTIFY_SIGNAL as well.

However, both the usermodehelper pipe and the coredump socket will bail early on TIF_NOTIFY_SIGNAL. This affects the following codepaths:

- coredump_sock_recv() -> unix_stream_read_generic()
The request/ack handshake is abandoned before any coredump data is sent.

- anon_pipe_write() returning -ERESTARTSYS Once the pipe is full this truncates the coredump.

- unix_stream_sendmsg() returning -ERESTARTSYS Once the send buffer is full this truncates the coredump.

- coredump_sock_wait() -> __kernel_read()
This reports a failure that didn't happen.

- wait_for_dump_helpers() -> wait_event_interruptible() This stops waiting for the coredump helpers.

Such truncation is entirely invisible to userspace and all uapi bits still indicate that a successful coredump happened. A crashing process with a bunch of file backed mappings and io_uring thrown in loses most of the coredump data. If the NT_FILE note goes past PAGE_SIZE mappings it's gonzo.

TIF_NOTIFY_SIGNAL is sent by io_uring for the common case. And it uses poll without sleeping so a completion callback runs task_work_add() from interrupt context against the task that submitted the request. This is the task that is running the coredump. Since that task hasn't set work_exited (it hasn't exited yet after all) TIF_NOTIFY_SIGNAL keeps reappearing.

A coredumping task doesn't return to userspace. The task work is run at exit. So interrupting it doesn't buy anything and just loses the coredump which is quite valuable.

Note that this isn't specific to io_uring. There's also klp_send_signals(), bpf_task_work_schedule_signal(), landlock's tsync and then technically, kthread_stop() and the printk kunit test set the bit raw.

---
 fs/coredump.c | 2 ++
 1 file changed, 2 insertions(+)

index d23c57eb2e058..6418f3eeeae7e 100644
@@ -630,6 +630,8 @@ void do_coredump(const kernel_siginfo_t *siginfo)
 	if (retval < 0)
 		goto fail_creds;
 
+	/* Task work must not cut the dump short, see signal_pending(). */
+	guard(no_notify_signal)();
 	old_cred = override_creds(cred);
 
 	ispipe = format_corename(&cn, &cprm, &argv, &argc);

2.53.0