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MIPS: Fix endless loop when processing signals for kernel tasks

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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>
This commit is contained in:
Dmitry Adamushko 2012-04-05 20:37:34 +02:00 committed by Ralf Baechle
parent 2d33976fb3
commit c90e6fbb22
1 changed files with 6 additions and 1 deletions
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7
arch/mips/kernel/entry.S
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@ -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