[PATCH 1/3] signal: In get_signal test for signal_group_exit every time through the loop

Eric W. Biederman
2021-11-16T05:33:24Z

Recently while investigating a problem with rr and signals I noticed
that siglock is dropped in ptrace_signal and get_signal does not jump
to relock.

Looking farther to see if the problem is anywhere else I see that
do_signal_stop also returns if signal_group_exit is true. I believe
that test can now never be true, but it is a bit hard to trace
through and be certain.

Testing signal_group_exit is not expensive, so move the test for
signal_group_exit into the for loop inside of get_signal to ensure
the test is never skipped improperly.

This has been a potential since I added the test for signal_group_exit
was added.

Fixes: 35634ffa1751 ("signal: Always notice exiting tasks")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
kernel/signal.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/kernel/signal.c b/kernel/signal.c
index 7c4b7ae714d4..986fa69c15c5 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2662,19 +2662,19 @@ bool get_signal(struct ksignal *ksig)
goto relock;
}

- /* Has this task already been marked for death? */
- if (signal_group_exit(signal)) {
- ksig->info.si_signo = signr = SIGKILL;
- sigdelset(&current->pending.signal, SIGKILL);
- trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
- &sighand->action[SIGKILL - 1]);
- recalc_sigpending();
- goto fatal;
- }
-
for (;;) {
struct k_sigaction *ka;

+ /* Has this task already been marked for death? */
+ if (signal_group_exit(signal)) {
+ ksig->info.si_signo = signr = SIGKILL;
+ sigdelset(&current->pending.signal, SIGKILL);
+ trace_signal_deliver(SIGKILL, SEND_SIG_NOINFO,
+ &sighand->action[SIGKILL - 1]);
+ recalc_sigpending();
+ goto fatal;
+ }
+
if (unlikely(current->jobctl & JOBCTL_STOP_PENDING) &&
do_signal_stop(0))
goto relock;
--
2.20.1