signal: Replace BUG_ON()s

[ Upstream commit 7f8af7bac5380f2d95a63a6f19964e22437166e1 ]

These really can be handled gracefully without killing the machine.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 0f9c27fbb8a52c50ff7d2659386f1f43e7fbddee)
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>