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authorDmitry Adamushko <dmitry.adamushka_ext@softathome.com>2012-04-05 20:37:34 +0200
committerRalf Baechle <ralf@linux-mips.org>2012-12-05 19:59:00 +0100
commitc90e6fbb220d44988cb65af3707367c57cdb65a8 (patch)
treeb007883a08b72d2a3a22c12c91ceaf139e014373
parent2d33976fb395a5b9cb00f2c24132b3f272eb9a9d (diff)
downloadlinux-c90e6fbb220d44988cb65af3707367c57cdb65a8.tar.bz2
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 <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>
-rw-r--r--arch/mips/kernel/entry.S7
1 files changed, 6 insertions, 1 deletions
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