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| author | Dmitry Adamushko <dmitry.adamushka_ext@softathome.com> | 2012-04-05 20:37:34 +0200 |
|---|---|---|
| committer | Ralf Baechle <ralf@linux-mips.org> | 2012-12-05 19:59:00 +0100 |
| commit | c90e6fbb220d44988cb65af3707367c57cdb65a8 (patch) | |
| tree | b007883a08b72d2a3a22c12c91ceaf139e014373 | |
| parent | MIPS: R3000/R3081: Fix CPU detection. (diff) | |
| download | linux-c90e6fbb220d44988cb65af3707367c57cdb65a8.tar.xz linux-c90e6fbb220d44988cb65af3707367c57cdb65a8.zip | |
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.S | 7 |
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 |