Re: [RFC,PATCH 2/2] kill_pid_info: don't take now unneeded tasklist_lock

[Oleg Nesterov]

On 03/17, Atsushi Tsuji wrote:
>
> (2008/03/05 3:57), Oleg Nesterov wrote:
> >Previously handle_stop_signal(SIGCONT) could drop ->siglock. That is why
> >kill_pid_info(SIGCONT) takes tasklist_lock to make sure the target task
> >can't go away after unlock. Not needed now.
> >
> >Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> 
> Hi Oleg,
> 
> I tried your patches on vanila kernel 2.6.25-rc3 (ia64).  Then, I got
> the NULL pointer dereference at task_session_nr(t) in
> check_kill_permission(). That is why t->signal->__session is accessed
> after t->signal was released.  It is reproducible by sending many
> SIGCONT signals to exiting processes.

Ah. Indeed!!! Thanks a lot Atsushi.

Note that check_kill_permission() is the last user of the deprecated
signal->__session/session, I was going to change this code later, but
missed the issue you pointed out.

I'll make the patch tomorrow.

Thanks!

Oleg.

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