Messages in this thread | | | Date | Sun, 5 May 2013 02:05:28 +0200 | From | Pavel Machek <> | Subject | Re: [PATCH 2/2] lockdep: check that no locks held at freeze time |
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Hi!
> >> >> --- a/kernel/exit.c > >> >> +++ b/kernel/exit.c > >> >> @@ -835,7 +835,7 @@ void do_exit(long code) > >> >> /* > >> >> * Make sure we are holding no locks: > >> >> */ > >> >> - debug_check_no_locks_held(tsk); > >> >> + debug_check_no_locks_held(); > >> > > >> > Is task guaranteed == current? > >> > >> Yes, the first line of do_exit is: > >> struct task_struct *tsk = current; > > > > Aha, I understand it now. > > > > Accessing current is slower than local variable. So your "new" code > > will work but will be slower. Please revert this part. > > Using current instead of passing in tsk was done at Andrew Morton's > suggestion, and makes no difference from the freezer's perspective > since it would have to use current to get the task to pass in, so I'm > going to leave it as is.
Well, current is:
static inline struct thread_info *current_thread_info(void) { register unsigned long sp asm ("sp"); return (struct thread_info *)(sp & ~(THREAD_SIZE - 1)); }
#define get_current() (current_thread_info()->task)
#define current get_current()
Instead of passing computed value to debug_check_no_locks_held(), you force it to be computed again. do_exit() performance matters for configure scripts, etc.
I'd say it makes sense to keep the optimalization. akpm can correct me.
Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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