2006-03-23 18:26:01

by Oleg Nesterov

Subject: [PATCH 2.6.16-mm1] cleanup __exit_signal->cleanup_sighand path

This patch moves 'tsk->sighand = NULL' from cleanup_sighand() to
__exit_signal(). This makes the exit path more understandable and
allows us to do cleanup_sighand() outside of ->siglock protected
section.

Signed-off-by: Oleg Nesterov <[email protected]>

--- MM/include/linux/sched.h~1_ESCS 2006-03-23 22:48:10.000000000 +0300
+++ MM/include/linux/sched.h 2006-03-23 23:00:02.000000000 +0300
@@ -1184,7 +1184,7 @@ extern void exit_thread(void);

extern void exit_files(struct task_struct *);
extern void __cleanup_signal(struct signal_struct *);
-extern void cleanup_sighand(struct task_struct *);
+extern void __cleanup_sighand(struct sighand_struct *);
extern void exit_itimers(struct signal_struct *);

extern NORET_TYPE void do_group_exit(int);
--- MM/kernel/fork.c~1_ESCS 2006-03-23 22:48:10.000000000 +0300
+++ MM/kernel/fork.c 2006-03-23 22:59:33.000000000 +0300
@@ -808,12 +808,8 @@ static inline int copy_sighand(unsigned
return 0;
}

-void cleanup_sighand(struct task_struct *tsk)
+void __cleanup_sighand(struct sighand_struct *sighand)
{
- struct sighand_struct * sighand = tsk->sighand;
-
- /* Ok, we're done with the signal handlers */
- tsk->sighand = NULL;
if (atomic_dec_and_test(&sighand->count))
kmem_cache_free(sighand_cachep, sighand);
}
@@ -1232,7 +1228,7 @@ bad_fork_cleanup_mm:
bad_fork_cleanup_signal:
cleanup_signal(p);
bad_fork_cleanup_sighand:
- cleanup_sighand(p);
+ __cleanup_sighand(p->sighand);
bad_fork_cleanup_fs:
exit_fs(p); /* blocking */
bad_fork_cleanup_files:
--- MM/kernel/exit.c~1_ESCS 2006-03-23 22:48:10.000000000 +0300
+++ MM/kernel/exit.c 2006-03-23 23:02:53.000000000 +0300
@@ -114,10 +114,11 @@ static void __exit_signal(struct task_st
__unhash_process(tsk);

tsk->signal = NULL;
- cleanup_sighand(tsk);
+ tsk->sighand = NULL;
spin_unlock(&sighand->siglock);
rcu_read_unlock();

+ __cleanup_sighand(sighand);
clear_tsk_thread_flag(tsk,TIF_SIGPENDING);
flush_sigqueue(&tsk->pending);
if (sig) {

2006-03-24 18:35:32

by Suzanne Wood

Subject: Re: [PATCH 2.6.16-mm1] cleanup __exit_signal->cleanup_sighand path

Thank you. This looks good. It clarifies the setting of tsk->sighand to NULL
before releasing siglock as you suggested earlier on LKML.

And it addresses all the occurrences in the mm-kernel of cleanup_sighand() to
become __cleanup_sighand() with the different argument -- paralleling the
__cleanup_signal().

The patch draws attention to __exit_signal() of fork.c and when the decremented
sig->count doesn't go to zero, the 'else' branch of the conditional, after
incrementing several counter fields of sig, sets sig to NULL to morph it
into a flag -- interesting.
Thanks.
Suzanne

> From Oleg Nesterov Thu Mar 23 10:59:36 2006

> This patch moves 'tsk->sighand = NULL' from cleanup_sighand() to
> __exit_signal(). This makes the exit path more understandable and
> allows us to do cleanup_sighand() outside of ->siglock protected
> section.

> Signed-off-by: Oleg Nesterov <[email protected]>

> --- MM/include/linux/sched.h~1_ESCS 2006-03-23 22:48:10.000000000 +0300
> +++ MM/include/linux/sched.h 2006-03-23 23:00:02.000000000 +0300
> @@ -1184,7 +1184,7 @@ extern void exit_thread(void);
>
> extern void exit_files(struct task_struct *);
> extern void __cleanup_signal(struct signal_struct *);
> -extern void cleanup_sighand(struct task_struct *);
> +extern void __cleanup_sighand(struct sighand_struct *);
> extern void exit_itimers(struct signal_struct *);
>
> extern NORET_TYPE void do_group_exit(int);
> --- MM/kernel/fork.c~1_ESCS 2006-03-23 22:48:10.000000000 +0300
> +++ MM/kernel/fork.c 2006-03-23 22:59:33.000000000 +0300
> @@ -808,12 +808,8 @@ static inline int copy_sighand(unsigned
> return 0;
> }
>
> -void cleanup_sighand(struct task_struct *tsk)
> +void __cleanup_sighand(struct sighand_struct *sighand)
> {
> - struct sighand_struct * sighand = tsk->sighand;
> -
> - /* Ok, we're done with the signal handlers */
> - tsk->sighand = NULL;
> if (atomic_dec_and_test(&sighand->count))
> kmem_cache_free(sighand_cachep, sighand);
> }
> @@ -1232,7 +1228,7 @@ bad_fork_cleanup_mm:
> bad_fork_cleanup_signal:
> cleanup_signal(p);
> bad_fork_cleanup_sighand:
> - cleanup_sighand(p);
> + __cleanup_sighand(p->sighand);
> bad_fork_cleanup_fs:
> exit_fs(p); /* blocking */
> bad_fork_cleanup_files:
> --- MM/kernel/exit.c~1_ESCS 2006-03-23 22:48:10.000000000 +0300
> +++ MM/kernel/exit.c 2006-03-23 23:02:53.000000000 +0300
> @@ -114,10 +114,11 @@ static void __exit_signal(struct task_st
> __unhash_process(tsk);
>
> tsk->signal = NULL;
> - cleanup_sighand(tsk);
> + tsk->sighand = NULL;
> spin_unlock(&sighand->siglock);
> rcu_read_unlock();
>
> + __cleanup_sighand(sighand);
> clear_tsk_thread_flag(tsk,TIF_SIGPENDING);
> flush_sigqueue(&tsk->pending);
> if (sig) {