[PATCH v2 1/1] s390/signal: fix endless loop in do_signal

[PATCH v2 1/1] s390/signal: fix endless loop in do_signal

[Sumanth Korikkar]

No upstream commit exists: the problem addressed here is that 
'commit 75309018a24d ("s390: add support for TIF_NOTIFY_SIGNAL")' 
was backported to 5.10. This commit is broken, but nobody noticed
upstream, since shortly after s390 converted to generic entry with
'commit 75309018a24d ("s390: add support for TIF_NOTIFY_SIGNAL")', which
implicitly fixed the problem outlined below.

Thread flag is set to TIF_NOTIFY_SIGNAL for io_uring work.  The io work
user or syscall calls do_signal when either one of the TIF_SIGPENDING or
TIF_NOTIFY_SIGNAL flag is set.  However, do_signal does consider only
TIF_SIGPENDING signal and ignores TIF_NOTIFY_SIGNAL condition.  This
means get_signal is never invoked  for TIF_NOTIFY_SIGNAL and hence the
flag is not cleared, which results in an endless do_signal loop.

Reference: 'commit 788d0824269b ("io_uring: import 5.15-stable io_uring")'
Fixes: 75309018a24d ("s390: add support for TIF_NOTIFY_SIGNAL")
Cc: stable@vger.kernel.org  # 5.10.162
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
 arch/s390/kernel/signal.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/kernel/signal.c b/arch/s390/kernel/signal.c
index b27b6c1f058d..9e900a8977bd 100644
--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -472,7 +472,7 @@ void do_signal(struct pt_regs *regs)
 	current->thread.system_call =
 		test_pt_regs_flag(regs, PIF_SYSCALL) ? regs->int_code : 0;
 
-	if (test_thread_flag(TIF_SIGPENDING) && get_signal(&ksig)) {
+	if (get_signal(&ksig)) {
 		/* Whee!  Actually deliver the signal.  */
 		if (current->thread.system_call) {
 			regs->int_code = current->thread.system_call;
-- 
2.37.2

Re: [PATCH v2 1/1] s390/signal: fix endless loop in do_signal

[Greg KH]

On Wed, Feb 15, 2023 at 03:13:24PM +0100, Sumanth Korikkar wrote:
> No upstream commit exists: the problem addressed here is that 
> 'commit 75309018a24d ("s390: add support for TIF_NOTIFY_SIGNAL")' 
> was backported to 5.10. This commit is broken, but nobody noticed
> upstream, since shortly after s390 converted to generic entry with
> 'commit 75309018a24d ("s390: add support for TIF_NOTIFY_SIGNAL")', which
> implicitly fixed the problem outlined below.
> 
> Thread flag is set to TIF_NOTIFY_SIGNAL for io_uring work.  The io work
> user or syscall calls do_signal when either one of the TIF_SIGPENDING or
> TIF_NOTIFY_SIGNAL flag is set.  However, do_signal does consider only
> TIF_SIGPENDING signal and ignores TIF_NOTIFY_SIGNAL condition.  This
> means get_signal is never invoked  for TIF_NOTIFY_SIGNAL and hence the
> flag is not cleared, which results in an endless do_signal loop.
> 
> Reference: 'commit 788d0824269b ("io_uring: import 5.15-stable io_uring")'
> Fixes: 75309018a24d ("s390: add support for TIF_NOTIFY_SIGNAL")
> Cc: stable@vger.kernel.org  # 5.10.162
> Acked-by: Heiko Carstens <hca@linux.ibm.com>
> Acked-by: Sven Schnelle <svens@linux.ibm.com>
> Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
> ---
>  arch/s390/kernel/signal.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Now queued up, thanks.

greg k-h