MIPS: Fix endless loop when processing signals for kernel tasks

Dmitry Adamushko · ralfbaechle · commit c90e6fbb220d · 2012-12-05T19:59:00.000+01:00
The problem occurs [1] when a kernel-mode task returns from a system call with a pending signal. A real-life scenario is a child of 'khelper' returning from a failed kernel_execve() in ____call_usermodehelper() [ kernel/kmod.c ]. kernel_execve() fails due to a pending SIGKILL, which is the result of "kill -9 -1" (at least, busybox's init does it upon reboot). The loop is as follows: * syscall_exit_work: - work_pending: // start_of_the_loop - work_notifysig: - do_notify_resume() - do_signal() - if (!user_mode(regs)) return; - resume_userspace // TIF_SIGPENDING is still set - work_pending // so we call work_pending => goto // start_of_the_loop More information can be found in another LKML thread: http://www.serverphorums.com/read.php?12,457826 [1] The problem was also reproduced on !CONFIG_VM86 x86, and the following fix was accepted. http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=29a2e2836ff9ea65a603c89df217f4198973a74f Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/3571/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S
@@ -36,6 +36,11 @@ FEXPORT(ret_from_exception)
 FEXPORT(ret_from_irq)
 	LONG_S	s0, TI_REGS($28)
 FEXPORT(__ret_from_irq)
+/*
+ * We can be coming here from a syscall done in the kernel space,
+ * e.g. a failed kernel_execve().
+ */
+resume_userspace_check:
 	LONG_L	t0, PT_STATUS(sp)		# returning to kernel mode?
 	andi	t0, t0, KU_USER
 	beqz	t0, resume_kernel
@@ -162,7 +167,7 @@ work_notifysig:				# deal with pending signals and
 	move	a0, sp
 	li	a1, 0
 	jal	do_notify_resume	# a2 already loaded
-	j	resume_userspace
+	j	resume_userspace_check
 
 FEXPORT(syscall_exit_partial)
 	local_irq_disable		# make sure need_resched doesn't
