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authorDmitry Adamushko <dmitry.adamushko@gmail.com>2012-03-22 21:39:25 +0100
committerH. Peter Anvin <hpa@zytor.com>2012-03-22 13:50:25 -0700
commit29a2e2836ff9ea65a603c89df217f4198973a74f (patch)
tree8570ae8b4b95995497b69495a4c9db351d0d6720 /arch/x86/kernel/entry_32.S
parent446e1c86d51d0823e003a43a2b85c430efce2733 (diff)
x86-32: Fix endless loop when processing signals for kernel tasks
The problem occurs on !CONFIG_VM86 kernels [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_notify_sig: - 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 seen on MIPS. Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com> Link: http://lkml.kernel.org/r/1332448765.2299.68.camel@dimm Cc: Oleg Nesterov <oleg@redhat.com> Cc: Roland McGrath <roland@hack.frob.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: <stable@vger.kernel.org> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/kernel/entry_32.S')
-rw-r--r--arch/x86/kernel/entry_32.S17
1 files changed, 10 insertions, 7 deletions
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 79d97e68f042..7b784f4ef1e4 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -98,12 +98,6 @@
#endif
.endm
-#ifdef CONFIG_VM86
-#define resume_userspace_sig check_userspace
-#else
-#define resume_userspace_sig resume_userspace
-#endif
-
/*
* User gs save/restore
*
@@ -327,10 +321,19 @@ ret_from_exception:
preempt_stop(CLBR_ANY)
ret_from_intr:
GET_THREAD_INFO(%ebp)
-check_userspace:
+resume_userspace_sig:
+#ifdef CONFIG_VM86
movl PT_EFLAGS(%esp), %eax # mix EFLAGS and CS
movb PT_CS(%esp), %al
andl $(X86_EFLAGS_VM | SEGMENT_RPL_MASK), %eax
+#else
+ /*
+ * We can be coming here from a syscall done in the kernel space,
+ * e.g. a failed kernel_execve().
+ */
+ movl PT_CS(%esp), %eax
+ andl $SEGMENT_RPL_MASK, %eax
+#endif
cmpl $USER_RPL, %eax
jb resume_kernel # not returning to v8086 or userspace