Re: [PATCH] Fix signal race during process exit

[Andrew Morton]

Andrew Morton <akpm@xxxxxxxx> wrote:
>
> yes?

no.  It needs tasklist_lock as well, to keep the other CPU (which is doing
wait4) at bay.




Fix a race identified by Jeremy Kerr <jeremy@xxxxxxxxxxxxxxxxxxxxxx>: if
update_process_times() decides to deliver a signal due to process timer
expiry, it can race with __exit_sighand()'s freeing of task->sighand.

Fix that by clearing the per-process timer state in exit_notify(), while under
local_irq_disable() and under tasklist_lock.  tasklist_lock provides exclusion
wrt release_task()'s freeing of task->sighand and local_irq_disable() provides
exclusion wrt update_process_times()'s inspection of the per-process timer
state.


Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---

 25-akpm/kernel/exit.c |    7 +++++++
 1 files changed, 7 insertions(+)

diff -puN kernel/exit.c~really-fix-signal-race-during-process-exit kernel/exit.c
--- 25/kernel/exit.c~really-fix-signal-race-during-process-exit	2004-06-02 00:09:01.491659584 -0700
+++ 25-akpm/kernel/exit.c	2004-06-02 00:15:31.230410288 -0700
@@ -737,6 +737,13 @@ static void exit_notify(struct task_stru
 	tsk->flags |= PF_DEAD;
 
 	/*
+	 * Clear these here so that update_process_times() won't try to deliver
+	 * itimer signals to this task while it is in late exit.
+	 */
+	tsk->it_virt_incr = 0;
+	tsk->it_prof_value = 0;
+
+	/*
 	 * In the preemption case it must be impossible for the task
 	 * to get runnable again, so use "_raw_" unlock to keep
 	 * preempt_count elevated until we schedule().
_

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