* [PATCH 1/2] copy_process: cleanup bad_fork_cleanup_sighand
@ 2006-02-20 16:03 Oleg Nesterov
2006-02-20 16:07 ` Oleg Nesterov
2006-02-24 17:35 ` Paul E. McKenney
0 siblings, 2 replies; 3+ messages in thread
From: Oleg Nesterov @ 2006-02-20 16:03 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-kernel, Ingo Molnar, Paul E. McKenney, Eric W. Biederman,
Roland McGrath
The only caller of exit_sighand(tsk) is copy_process's error path.
We can call __exit_sighand() directly and kill exit_sighand().
This 'tsk' was not yet registered in pid_hash[] or init_task.tasks,
it has no external references, nobody can see it, and
IF (clone_flags & CLONE_SIGHAND)
At least 'current' has a reference to ->sighand, this
means atomic_dec_and_test(sighand->count) can't be true.
ELSE
Nobody can see this ->sighand, this means we can free it
without any locking.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
--- 2.6.16-rc3/include/linux/sched.h~1_SIGH 2006-02-18 22:13:44.000000000 +0300
+++ 2.6.16-rc3/include/linux/sched.h 2006-02-20 00:38:57.000000000 +0300
@@ -1143,7 +1143,6 @@ extern void exit_thread(void);
extern void exit_files(struct task_struct *);
extern void exit_signal(struct task_struct *);
extern void __exit_signal(struct task_struct *);
-extern void exit_sighand(struct task_struct *);
extern void __exit_sighand(struct task_struct *);
extern void exit_itimers(struct signal_struct *);
--- 2.6.16-rc3/kernel/signal.c~1_SIGH 2006-02-19 21:08:23.000000000 +0300
+++ 2.6.16-rc3/kernel/signal.c 2006-02-20 00:37:34.000000000 +0300
@@ -336,20 +336,6 @@ void __exit_sighand(struct task_struct *
kmem_cache_free(sighand_cachep, sighand);
}
-void exit_sighand(struct task_struct *tsk)
-{
- write_lock_irq(&tasklist_lock);
- rcu_read_lock();
- if (tsk->sighand != NULL) {
- struct sighand_struct *sighand = rcu_dereference(tsk->sighand);
- spin_lock(&sighand->siglock);
- __exit_sighand(tsk);
- spin_unlock(&sighand->siglock);
- }
- rcu_read_unlock();
- write_unlock_irq(&tasklist_lock);
-}
-
/*
* This function expects the tasklist_lock write-locked.
*/
--- 2.6.16-rc3/kernel/fork.c~1_SIGH 2006-02-18 01:11:59.000000000 +0300
+++ 2.6.16-rc3/kernel/fork.c 2006-02-20 00:38:39.000000000 +0300
@@ -1196,7 +1196,8 @@ bad_fork_cleanup_mm:
bad_fork_cleanup_signal:
exit_signal(p);
bad_fork_cleanup_sighand:
- exit_sighand(p);
+ if (p->sighand)
+ __exit_sighand(p);
bad_fork_cleanup_fs:
exit_fs(p); /* blocking */
bad_fork_cleanup_files:
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH 1/2] copy_process: cleanup bad_fork_cleanup_sighand
2006-02-20 16:03 [PATCH 1/2] copy_process: cleanup bad_fork_cleanup_sighand Oleg Nesterov
@ 2006-02-20 16:07 ` Oleg Nesterov
2006-02-24 17:35 ` Paul E. McKenney
1 sibling, 0 replies; 3+ messages in thread
From: Oleg Nesterov @ 2006-02-20 16:07 UTC (permalink / raw)
To: Andrew Morton, linux-kernel, Ingo Molnar, Paul E. McKenney,
Eric W. Biederman, Roland McGrath
Oleg Nesterov wrote:
>
>
> [PATCH 1/2] copy_process: cleanup bad_fork_cleanup_sighand
Err, sorry, should be "[PATCH 1/4]". The same for the next "2/2"
patch in series.
Oleg.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH 1/2] copy_process: cleanup bad_fork_cleanup_sighand
2006-02-20 16:03 [PATCH 1/2] copy_process: cleanup bad_fork_cleanup_sighand Oleg Nesterov
2006-02-20 16:07 ` Oleg Nesterov
@ 2006-02-24 17:35 ` Paul E. McKenney
1 sibling, 0 replies; 3+ messages in thread
From: Paul E. McKenney @ 2006-02-24 17:35 UTC (permalink / raw)
To: Oleg Nesterov
Cc: Andrew Morton, linux-kernel, Ingo Molnar, Eric W. Biederman,
Roland McGrath
On Mon, Feb 20, 2006 at 07:03:13PM +0300, Oleg Nesterov wrote:
> The only caller of exit_sighand(tsk) is copy_process's error path.
> We can call __exit_sighand() directly and kill exit_sighand().
>
> This 'tsk' was not yet registered in pid_hash[] or init_task.tasks,
> it has no external references, nobody can see it, and
>
> IF (clone_flags & CLONE_SIGHAND)
> At least 'current' has a reference to ->sighand, this
> means atomic_dec_and_test(sighand->count) can't be true.
>
> ELSE
> Nobody can see this ->sighand, this means we can free it
> without any locking.
This passes steamroller tests (which now work on ppc64, but that is another
story). Looks good to me!
Thanx, Paul
Acked-by: <paulmck@us.ibm.com>
> Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
>
> --- 2.6.16-rc3/include/linux/sched.h~1_SIGH 2006-02-18 22:13:44.000000000 +0300
> +++ 2.6.16-rc3/include/linux/sched.h 2006-02-20 00:38:57.000000000 +0300
> @@ -1143,7 +1143,6 @@ extern void exit_thread(void);
> extern void exit_files(struct task_struct *);
> extern void exit_signal(struct task_struct *);
> extern void __exit_signal(struct task_struct *);
> -extern void exit_sighand(struct task_struct *);
> extern void __exit_sighand(struct task_struct *);
> extern void exit_itimers(struct signal_struct *);
>
> --- 2.6.16-rc3/kernel/signal.c~1_SIGH 2006-02-19 21:08:23.000000000 +0300
> +++ 2.6.16-rc3/kernel/signal.c 2006-02-20 00:37:34.000000000 +0300
> @@ -336,20 +336,6 @@ void __exit_sighand(struct task_struct *
> kmem_cache_free(sighand_cachep, sighand);
> }
>
> -void exit_sighand(struct task_struct *tsk)
> -{
> - write_lock_irq(&tasklist_lock);
> - rcu_read_lock();
> - if (tsk->sighand != NULL) {
> - struct sighand_struct *sighand = rcu_dereference(tsk->sighand);
> - spin_lock(&sighand->siglock);
> - __exit_sighand(tsk);
> - spin_unlock(&sighand->siglock);
> - }
> - rcu_read_unlock();
> - write_unlock_irq(&tasklist_lock);
> -}
> -
> /*
> * This function expects the tasklist_lock write-locked.
> */
> --- 2.6.16-rc3/kernel/fork.c~1_SIGH 2006-02-18 01:11:59.000000000 +0300
> +++ 2.6.16-rc3/kernel/fork.c 2006-02-20 00:38:39.000000000 +0300
> @@ -1196,7 +1196,8 @@ bad_fork_cleanup_mm:
> bad_fork_cleanup_signal:
> exit_signal(p);
> bad_fork_cleanup_sighand:
> - exit_sighand(p);
> + if (p->sighand)
> + __exit_sighand(p);
> bad_fork_cleanup_fs:
> exit_fs(p); /* blocking */
> bad_fork_cleanup_files:
^ permalink raw reply [flat|nested] 3+ messages in thread
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