FAILED: patch "[PATCH] signal: only SIGKILL and the freezers interrupt a coredumping" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 563d606b93d7a1d23512832fc252d32c68860d87
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026102833-anagram-laundry-e618@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 563d606b93d7a1d23512832fc252d32c68860d87 Mon Sep 17 00:00:00 2001
From: Christian Brauner <[email protected]>
Date: Tue, 22 Sep 2026 15:26:16 +0200
Subject: [PATCH] signal: only SIGKILL and the freezers interrupt a coredumping
task

For quite a while now coredump has allowed either SIGKILL or freezing to interrupt an ongoing coredump. Since we seem to like it complicated "freezing" can mean a lot of things:

(1) Power Management induced freezing
(2) cgroup v1 freezer controller induced freezing
(3) cgroup v2 freezer controller induced freezing

So (1) and (2) are handled by checking freezing() but (3) isn't.
(3) uses cgroup_freeze_task() which sets JOBCTL_TRAP_FREEZE and calls signal_wake_up() on every task in the cgroup. The trap isn't handled by the coredump code.

Which means the current logic is inconsistent. Power and cgroup v1 freeze and abort the coredump. With cgroup v2 it depends on where the core goes. A dump to a file completes and the cgroup v2 freeze has to wait for it to finish. When dumping to a pipe or socket the dump is interrupted at the next write because of trap's TIF_SIGPENDING. Which is it? Let's be consistent and align (1)-(3): freezing interrupts an ongoing coredump and doesn't make it wait until the dump is done.

All three freezers go through signal_wake_up() and so set TIF_SIGPENDING on the dumper. And once zap_threads() has set core_state that flag can't mean anything else anymore. prepare_signal() drops every signal but SIGKILL for the group, the dying threads don't retarget shared signals to the dumper, and zap_process() cleared the pending job control traps. So the flag is the thing to check. Let dump_interrupted() test task_sigpending() and nothing else. That is also what the pipe and socket writes already fail on. TIF_NOTIFY_SIGNAL is left out on purpose, task work must not cut a dump short.

A seized tracee that gets PTRACE_INTERRUPT during the dump is cut short the same way. It already was for pipes and sockets.

The one freeze that check can miss is one requested before the dump started. zap_threads() clears TIF_SIGPENDING and the cgroup v2 freezer only wakes a task once while its JOBCTL_TRAP_FREEZE isn't part of JOBCTL_PENDING_MASK and survives zap_process(). So refuse to start the dump when freezing() is true or the trap is pending. The task then exits without dumping, which is what happens today when the freeze interrupts the dump at the first write.

index d88a65e37ee1..af09a4660341 100644
@@ -508,7 +508,9 @@ static int zap_threads(struct task_struct *tsk,
 	int nr = -EAGAIN;
 
 	spin_lock_irq(&tsk->sighand->siglock);
-	if (!(signal->flags & SIGNAL_GROUP_EXIT) && !signal->group_exec_task) {
+	/* A freeze requested before the dump would be lost with TIF_SIGPENDING. */
+	if (!(signal->flags & SIGNAL_GROUP_EXIT) && !signal->group_exec_task &&
+	    !freezing(tsk) && !(tsk->jobctl & JOBCTL_TRAP_FREEZE)) {
 		/* Allow SIGKILL, see prepare_signal() */
 		signal->core_state = core_state;
 		nr = zap_process(signal, exit_code);

@@ -580,13 +582,8 @@ static void coredump_finish(bool core_dumped)
 
 static bool dump_interrupted(void)
 {
-	/*
-	 * SIGKILL or freezing() interrupt the coredumping. Perhaps we
-	 * can do try_to_freeze() and check __fatal_signal_pending(),
-	 * but then we need to teach dump_write() to restart and clear
-	 * TIF_SIGPENDING.
-	 */
-	return fatal_signal_pending(current) || freezing(current);
+	/* Only SIGKILL and the freezers set it after zap_threads(). */
+	return task_sigpending(current);
 }
 
 static void wait_for_dump_helpers(struct file *file)

From: Christian Brauner <[email protected]>

[ Upstream commit 563d606b93d7a1d23512832fc252d32c68860d87 ]

For quite a while now coredump has allowed either SIGKILL or freezing to interrupt an ongoing coredump. Since we seem to like it complicated "freezing" can mean a lot of things:

(1) Power Management induced freezing
(2) cgroup v1 freezer controller induced freezing
(3) cgroup v2 freezer controller induced freezing

So (1) and (2) are handled by checking freezing() but (3) isn't.
(3) uses cgroup_freeze_task() which sets JOBCTL_TRAP_FREEZE and calls signal_wake_up() on every task in the cgroup. The trap isn't handled by the coredump code.

Which means the current logic is inconsistent. Power and cgroup v1 freeze and abort the coredump. With cgroup v2 it depends on where the core goes. A dump to a file completes and the cgroup v2 freeze has to wait for it to finish. When dumping to a pipe or socket the dump is interrupted at the next write because of trap's TIF_SIGPENDING. Which is it? Let's be consistent and align (1)-(3): freezing interrupts an ongoing coredump and doesn't make it wait until the dump is done.

All three freezers go through signal_wake_up() and so set TIF_SIGPENDING on the dumper. And once zap_threads() has set core_state that flag can't mean anything else anymore. prepare_signal() drops every signal but SIGKILL for the group, the dying threads don't retarget shared signals to the dumper, and zap_process() cleared the pending job control traps. So the flag is the thing to check. Let dump_interrupted() test task_sigpending() and nothing else. That is also what the pipe and socket writes already fail on. TIF_NOTIFY_SIGNAL is left out on purpose, task work must not cut a dump short.

A seized tracee that gets PTRACE_INTERRUPT during the dump is cut short the same way. It already was for pipes and sockets.

The one freeze that check can miss is one requested before the dump started. zap_threads() clears TIF_SIGPENDING and the cgroup v2 freezer only wakes a task once while its JOBCTL_TRAP_FREEZE isn't part of JOBCTL_PENDING_MASK and survives zap_process(). So refuse to start the dump when freezing() is true or the trap is pending. The task then exits without dumping, which is what happens today when the freeze interrupts the dump at the first write.

---
 fs/coredump.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

index 5e5c1d72d63bc..0f0aab402a37a 100644
@@ -409,7 +409,9 @@ static int zap_threads(struct task_struct *tsk, struct mm_struct *mm,
 	int nr = -EAGAIN;
 
 	spin_lock_irq(&tsk->sighand->siglock);
-	if (!signal_group_exit(tsk->signal)) {
+	/* A freeze requested before the dump would be lost with TIF_SIGPENDING. */
+	if (!signal_group_exit(tsk->signal) &&
+	    !freezing(tsk) && !(tsk->jobctl & JOBCTL_TRAP_FREEZE)) {
 		mm->core_state = core_state;
 		tsk->signal->group_exit_task = tsk;
 		nr = zap_process(tsk, exit_code, 0);

@@ -545,13 +547,8 @@ static void coredump_finish(struct mm_struct *mm, bool core_dumped)
 
 static bool dump_interrupted(void)
 {
-	/*
-	 * SIGKILL or freezing() interrupt the coredumping. Perhaps we
-	 * can do try_to_freeze() and check __fatal_signal_pending(),
-	 * but then we need to teach dump_write() to restart and clear
-	 * TIF_SIGPENDING.
-	 */
-	return fatal_signal_pending(current) || freezing(current);
+	/* Only SIGKILL and the freezers set it after zap_threads(). */
+	return task_sigpending(current);
 }
 
 static void wait_for_dump_helpers(struct file *file)

2.53.0