[PATCH AUTOSEL 5.10 38/39] signal: don't allow STOP on PF_IO_WORKER threads

From: Sasha Levin
Date: Thu Mar 25 2021 - 07:33:01 EST


From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>

[ Upstream commit 4db4b1a0d1779dc159f7b87feb97030ec0b12597 ]

Just like we don't allow normal signals to IO threads, don't deliver a
STOP to a task that has PF_IO_WORKER set. The IO threads don't take
signals in general, and have no means of flushing out a stop either.

Longer term, we may want to look into allowing stop of these threads,
as it relates to eg process freezing. For now, this prevents a spin
issue if a SIGSTOP is delivered to the parent task.

Reported-by: Stefan Metzmacher <metze@xxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
kernel/signal.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 18ed1f853439..1d901a789812 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -288,7 +288,8 @@ bool task_set_jobctl_pending(struct task_struct *task, unsigned long mask)
JOBCTL_STOP_SIGMASK | JOBCTL_TRAPPING));
BUG_ON((mask & JOBCTL_TRAPPING) && !(mask & JOBCTL_PENDING_MASK));

- if (unlikely(fatal_signal_pending(task) || (task->flags & PF_EXITING)))
+ if (unlikely(fatal_signal_pending(task) ||
+ (task->flags & (PF_EXITING | PF_IO_WORKER))))
return false;

if (mask & JOBCTL_STOP_SIGMASK)
--
2.30.1