So did I overlook something that makes it a non-issue on the recent mips?
On 5 April 2012 20:37, dimm <[email protected]> wrote:
> From: Dmitry Adamushko <[email protected]>
>
> 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 <[email protected]>
> Cc: Ralf Baechle <[email protected]>
> Cc: [email protected]
>
> --- arch/mips/kernel/entry.S.old ? ? ? ?2012-04-05 10:57:12.500976124 +0200
> +++ arch/mips/kernel/entry.S ? ?2012-04-05 11:21:24.128174358 +0200
> @@ -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 s
> ? ? ? ?move ? ?a0, sp
> ? ? ? ?li ? ? ?a1, 0
> ? ? ? ?jal ? ? do_notify_resume ? ? ? ?# a2 already loaded
> - ? ? ? j ? ? ? resume_userspace
> + ? ? ? j ? ? ? resume_userspace_check
>
> ?FEXPORT(syscall_exit_work_partial)
> ? ? ? ?SAVE_STATIC
>
>
--
-- Dmitry