Messages in this thread | | | Date | Thu, 25 Nov 2010 13:28:00 +0200 | From | Sergey Senozhatsky <> | Subject | Re: rcu_read_lock/unlock protect find_task_by_vpid call in posix_cpu_timer_create |
| |
Hello,
On (11/25/10 12:02), Oleg Nesterov wrote: > (another try, actually add Sergey) > Thank you.
> On 11/25, Peter Zijlstra wrote: > > > > On Wed, 2010-11-24 at 20:09 -0500, Dave Jones wrote: > > > --- a/kernel/posix-cpu-timers.c > > > +++ b/kernel/posix-cpu-timers.c > > > @@ -391,6 +391,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) > > > INIT_LIST_HEAD(&new_timer->it.cpu.entry); > > > > > > read_lock(&tasklist_lock); > > > + rcu_read_lock(); > > > if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) { > > > if (pid == 0) { > > > p = current; > > > @@ -414,6 +415,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) > > > } else { > > > ret = -EINVAL; > > > } > > > + rcu_read_unlock(); > > > read_unlock(&tasklist_lock); > > > > > > return ret; > > > > Do we still need the tasklist_lock in this case? > > No. posix-cpu-timer.c shouldn't use tasklist at all. But it is not > completely trivial to remove it. > > In particular, this patch is not exactly right, we can't trust > thread_group_leader() without tasklist. > > Sergey already sent the patch which removes tasklist from > posix_cpu_timer_create() and posix_cpu_timer_create(), and iirc > Thomas queued it. >
You're right, Oleg.
Commit-ID: c0deae8c9587419ab13874b74425ce2eb2e18508 Gitweb: http://git.kernel.org/tip/c0deae8c9587419ab13874b74425ce2eb2e18508 Author: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> AuthorDate: Wed, 3 Nov 2010 18:52:56 +0200 Committer: Thomas Gleixner <tglx@linutronix.de> CommitDate: Wed, 10 Nov 2010 13:07:06 +0100
posix-cpu-timers: Rcu_read_lock/unlock protect find_task_by_vpid call
queued (15 days so far).
> > Also, why is that think complaining, surely the tasklist_lock pins any > > and all PID objects? > > The only problem is: if copy_process() fails, it does free_pid() > lockless. This means, without rcu lock it is not safe to scan the > rcu-protected lists. > > We can change copy_process() (in fact I sent the patch several > years ago), but everybody think that find_pid/etc should always > take rcu_read_lock() instead. I tend to agree. > > Oleg. >
Sergey[unhandled content-type:application/pgp-signature] | |