Re: [PATCH] Don't apply for write lock on tasklist_lock if parentdoesn't ptrace other processes
From: Oleg Nesterov
Date: Fri Jul 23 2010 - 13:43:31 EST
On 07/22, Roland McGrath wrote:
>
> > So, this list_empty() check needs taskslit at least for reading. But, we
> > are going to take it for writing right after exit_ptrace() returns, afaics
> > we can add this fastpatch check for free.
>
> That looks good to me, but it could use some more scare comments.
Good. Hopfully Zhang can test it to confirm it has the same effect.
It should, but I am still wondering about 10% improvement.
> > /*
> > - * Detach all tasks we were using ptrace on.
> > + * Detach all tasks we were using ptrace on. Called with tasklist held.
>
> * Called with tasklist held for writing, and returns with it held too.
> * But note it can release and reacquire the lock.
OK.
> > + write_lock_irq(&tasklist_lock);
> > +
> /*
> * Note that exit_ptrace() might drop tasklist_lock and reacquire it.
> */
> > exit_ptrace(father);
Well, this comment a bit "unfair", please see below.
> > - write_lock_irq(&tasklist_lock);
> > reaper = find_new_reaper(father);
Note that find_new_reaper() can drop/reacquire tasklist too.
Perhaps,
/* These two might drop and reacquire tasklist_lock */
exit_ptrace(father);
reaper = find_new_reaper(father);
...
?
Oleg.
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