[PATCH] sched: __fatal_signal_pending() should also check shared signals

[Tycho Andersen]

The wait_* code uses signal_pending_state() to test whether a thread has
been interrupted, which ultimately uses __fatal_signal_pending() to detect
if there is a fatal signal.

When a pid ns dies, in zap_pid_ns_processes() it does:

    group_send_sig_info(SIGKILL, SEND_SIG_PRIV, task, PIDTYPE_MAX);

for all the tasks in the pid ns. That calls through:

    group_send_sig_info() ->
      do_send_sig_info() ->
        send_signal_locked() ->
          __send_signal_locked()

which does:

    pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;

which puts sigkill in the set of shared signals, but not the individual
pending ones. If tasks are stuck in a killable wait (e.g. a fuse flush
operation), they won't see this shared signal, and will hang forever, since
TIF_SIGPENDING is set, but the fatal signal can't be detected.

Signed-off-by: Tycho Andersen <tycho@tycho.pizza>
---
 include/linux/sched/signal.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h
index cafbe03eed01..a033ccb0a729 100644
--- a/include/linux/sched/signal.h
+++ b/include/linux/sched/signal.h
@@ -402,7 +402,8 @@ static inline int signal_pending(struct task_struct *p)
 
 static inline int __fatal_signal_pending(struct task_struct *p)
 {
-	return unlikely(sigismember(&p->pending.signal, SIGKILL));
+	return unlikely(sigismember(&p->pending.signal, SIGKILL) ||
+			sigismember(&p->signal->shared_pending.signal, SIGKILL));
 }
 
 static inline int fatal_signal_pending(struct task_struct *p)

base-commit: 32346491ddf24599decca06190ebca03ff9de7f8
-- 
2.34.1