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| author | Dmitry Adamushko <dmitry.adamushko@gmail.com> | 2012-03-22 21:39:25 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-04-02 09:27:17 -0700 |
| commit | 6986f38042842b6c43dd10c36311db66c2865367 (patch) | |
| tree | f50a8f39ff58d01ec1edf09a4bf760e5579a86e9 | |
| parent | d6dbbeccac70f85972e8b7773cede113914c9730 (diff) | |
| download | lwn-6986f38042842b6c43dd10c36311db66c2865367.tar.gz lwn-6986f38042842b6c43dd10c36311db66c2865367.zip | |
x86-32: Fix endless loop when processing signals for kernel tasks
commit 29a2e2836ff9ea65a603c89df217f4198973a74f upstream.
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>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/x86/kernel/entry_32.S | 17 |
1 files changed, 10 insertions, 7 deletions
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S index 5c1a91974918..edb3d46c16db 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 |