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SubjectRe: [PATCH] rcu: Fix opposite might_sleep() check in rcu_blocking_is_gp()
On Sat, Dec 17, 2022 at 02:44:47AM +0000, Zhang, Qiang1 wrote:
>
> On Thu, Dec 15, 2022 at 11:57:55AM +0800, Zqiang wrote:
> > Currently, if the system is in the RCU_SCHEDULER_INACTIVE state, invoke
> > synchronize_rcu_*() will implies a grace period and return directly,
> > so there is no sleep action due to waiting for a grace period to end,
> > but this might_sleep() check is the opposite. therefore, this commit
> > puts might_sleep() check in the correct palce.
> >
> > Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> >
> >Queued for testing and review, thank you!
> >
> >I was under the impression that might_sleep() did some lockdep-based
> >checking, but I am unable to find it. If there really is such checking,
> >that would be a potential argument for leaving this code as it is.
> >
> >
> >__might_sleep
> > __might_resched(file, line, 0)
> > rcu_sleep_check()
> >
> >Does it refer to this rcu_sleep_check() ?
> >
> >If so, when in the RCU_SCHEDULER_INACTIVE state, the debug_lockdep_rcu_enabled() is always
> >return false, so the RCU_LOCKDEP_WARN() also does not produce an actual warning.
>
> and when the system_state == SYSTEM_BOOTING, we just did rcu_sleep_check() and then return.

Very good, thank you!

Thoughts from others?

Thanx, Paul

> Thanks
> Zqiang
>
> >Thanks
> >Zqiang
> >
>
> >But in the meantime, full speed ahead! ;-)
> >
> > Thanx, Paul
> >
> > ---
> > kernel/rcu/tree.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index ee8a6a711719..65f3dd2fd3ae 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -3379,9 +3379,10 @@ void __init kfree_rcu_scheduler_running(void)
> > */
> > static int rcu_blocking_is_gp(void)
> > {
> > - if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
> > + if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) {
> > + might_sleep();
> > return false;
> > - might_sleep(); /* Check for RCU read-side critical section. */
> > + }
> > return true;
> > }
> >
> > --
> > 2.25.1
> >

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