Re: TASK_WAKEKILL && /sbin/init (was: [PATCH 1/2] schedule: fix TASK_WAKEKILL vs SIGKILL race)

[Matthew Wilcox <matthew@wil.cx>]

On Thu, Jun 05, 2008 at 07:23:16PM +0400, Oleg Nesterov wrote:
> Sorry Matthew, I left this part unanswered because I didn't have the
> time yesterday...

That's OK, thanks for picking it up again.

> On 06/04, Matthew Wilcox wrote:
> >
> > On Wed, Jun 04, 2008 at 09:09:05PM +0400, Oleg Nesterov wrote:
> > > Note also that with or without this patch TASK_WAKEKILL is not exactly right
> > > wrt /sbin/init, but this is another issue.
> >
> > That's certainly an interesting conversation to have.
> 
> If lock_page_killable() fails because the task was killed by SIGKILL or
> another fatal signal, do_generic_file_read() returns -EIO.
> 
> This seems to be OK, because in fact the userspace won't see this error, the
> task will dequeue SIGKILL and exit.
> 
> However, /sbin/init is different, it will dequeue SIGKILL, ignore it, and be
> confused by this bogus -EIO. Please note that while this bug is not likely,
> it is _not_ theoretical. It does happen that user-space sends the unhandled
> fatal signals to init.

Have you actually tested this?  I thought it was handled by:

                /*
                 * Global init gets no signals it doesn't want.
                 */
                if (unlikely(signal->flags & SIGNAL_UNKILLABLE) &&
                    !signal_group_exit(signal))
                        continue;

in get_signal_to_deliver().

-- 
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