When a periodic POSIX timer fires while its target signal is ignored
(e.g. default SIGCONT/SIGCHLD/SIGURG/SIGWINCH or SIG_IGN), the signal is
dropped without advancing or queueing the timer's sigqueue, leaving the
periodic timer stalled even after userspace installs a signal handler
via sigaction(). Check and re-arm any pending ignored POSIX timers on
the thread group when do_sigaction() transitions a signal out of the
ignored state.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
diff --git a/kernel/signal.c b/kernel/signal.c
index ec30550951ec..49ba188296c4 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -4351,7 +4351,7 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 	sigaction_compat_abi(act, oact);
 
 	if (act) {
-		bool was_ignored = k->sa.sa_handler == SIG_IGN;
+		bool was_ignored = sig_task_ignored(p, sig, false);
 
 		sigdelsetmask(&act->sa.sa_mask,
 			      sigmask(SIGKILL) | sigmask(SIGSTOP));
@@ -4367,7 +4367,7 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
 		 *   (for example, SIGCHLD), shall cause the pending signal to
 		 *   be discarded, whether or not it is blocked"
 		 */
-		if (sig_handler_ignored(sig_handler(p, sig), sig)) {
+		if (sig_task_ignored(p, sig, false)) {
 			sigemptyset(&mask);
 			sigaddset(&mask, sig);
 			flush_sigqueue_mask(p, &mask, &p->signal->shared_pending);

On 09/19, Hui Peng wrote:
>
> When a periodic POSIX timer fires while its target signal is ignored
> (e.g. default SIGCONT/SIGCHLD/SIGURG/SIGWINCH or SIG_IGN), the signal is
> dropped without advancing or queueing the timer's sigqueue, leaving the
> periodic timer stalled even after userspace installs a signal handler
> via sigaction(). Check and re-arm any pending ignored POSIX timers on
> the thread group when do_sigaction() transitions a signal out of the
> ignored state.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

Well, It was supposed to have been fixed by caf77435dd8a ("signal: Handle
ignored signals in do_sigaction(action != SIG_IGN)") and other commits in
that series...

Do you have a test-case?

Oleg.

> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>
> ---
> diff --git a/kernel/signal.c b/kernel/signal.c
> index ec30550951ec..49ba188296c4 100644
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -4351,7 +4351,7 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
>  	sigaction_compat_abi(act, oact);
>  
>  	if (act) {
> -		bool was_ignored = k->sa.sa_handler == SIG_IGN;
> +		bool was_ignored = sig_task_ignored(p, sig, false);
>  
>  		sigdelsetmask(&act->sa.sa_mask,
>  			      sigmask(SIGKILL) | sigmask(SIGSTOP));
> @@ -4367,7 +4367,7 @@ int do_sigaction(int sig, struct k_sigaction *act, struct k_sigaction *oact)
>  		 *   (for example, SIGCHLD), shall cause the pending signal to
>  		 *   be discarded, whether or not it is blocked"
>  		 */
> -		if (sig_handler_ignored(sig_handler(p, sig), sig)) {
> +		if (sig_task_ignored(p, sig, false)) {
>  			sigemptyset(&mask);
>  			sigaddset(&mask, sig);
>  			flush_sigqueue_mask(p, &mask, &p->signal->shared_pending);
>