So did I overlook something that makes it a non-issue on the recent mips? On 5 April 2012 20:37, dimm <dmitry.adamushko@xxxxxxxxx> wrote: > From: Dmitry Adamushko <dmitry.adamushka_ext@xxxxxxxxxxxxxx> > > 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@xxxxxxxxx> > Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> > Cc: linux-mips@xxxxxxxxxxxxxx > > --- 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
