From c90e6fbb220d44988cb65af3707367c57cdb65a8 Mon Sep 17 00:00:00 2001 From: Dmitry Adamushko Date: Thu, 5 Apr 2012 20:37:34 +0200 Subject: [PATCH] MIPS: Fix endless loop when processing signals for kernel tasks 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 Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/3571/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/entry.S | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S index a6c133212003..9b00362f32f6 100644 --- 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 -- 2.20.1