Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH 01/16] freezer: fix current->state restoration race in refrigerator() | Date | Fri, 19 Aug 2011 23:08:59 +0200 |
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On Friday, August 19, 2011, Tejun Heo wrote: > refrigerator() saves current->state before entering frozen state and > restores it before returning using __set_current_state(); however, > this is racy, for example, please consider the following sequence. > > set_current_state(TASK_INTERRUPTIBLE); > try_to_sleep();
Did you mean try_to_freeze() here?
> if (kthread_should_stop()) > break; > schedule(); > > If kthread_stop() races with ->state restoration, the restoration can > restore ->state to TASK_INTERRUPTIBLE after kthread_stop() sets it to > TASK_RUNNING but kthread_should_stop() may still see zero > ->should_stop because there's no memory barrier between restoring > TASK_INTERRUPTIBLE and kthread_should_stop() test. > > This isn't restricted to kthread_should_stop(). current->state is > often used in memory barrier based synchronization and silently > restoring it w/o mb breaks them. > > Use set_current_state() instead. > > Signed-off-by: Tejun Heo <tj@kernel.org> > --- > kernel/freezer.c | 8 +++++++- > 1 files changed, 7 insertions(+), 1 deletions(-) > > diff --git a/kernel/freezer.c b/kernel/freezer.c > index 7b01de9..575f863 100644 > --- a/kernel/freezer.c > +++ b/kernel/freezer.c > @@ -58,7 +58,13 @@ void refrigerator(void) > current->flags &= ~PF_FREEZING; > > pr_debug("%s left refrigerator\n", current->comm); > - __set_current_state(save); > + > + /* > + * Restore saved task state before returning. The mb'd version > + * needs to be used; otherwise, it might silently break > + * synchronization which depends on ordered task state change. > + */ > + set_current_state(save);
I think the change is correct.
> } > EXPORT_SYMBOL(refrigerator);
Thanks, Rafael
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