Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Thu, 21 Apr 2022 12:57:28 +0200 | Subject | Re: [PATCH 6/9] pm/irq: make for_each_irq_desc() safe of irq_desc release |
| |
On Thu, Apr 21, 2022 at 5:31 AM Pingfan Liu <kernelfans@gmail.com> wrote: > > On Wed, Apr 20, 2022 at 06:23:48PM +0200, Rafael J. Wysocki wrote: > > On Wed, Apr 20, 2022 at 4:06 PM Pingfan Liu <kernelfans@gmail.com> wrote: > > > > > > The invloved context is no a RCU read section. Furthermore there may be > > > more than one task at this point. Hence it demands a measure to prevent > > > irq_desc from freeing. Use irq_lock_sparse to serve the protection > > > purpose. > > > > Can you please describe an example scenario in which the added locking > > will prevent a failure from occurring? > > > > Sorry to forget mentioning that this is based on the code analysis. > > Suppose the following scenario: > Two threads invloved > threadA "hibernate" runs suspend_device_irqs() > threadB "rcu_cpu_kthread" runs rcu_core()->rcu_do_batch(), which releases > object, let's say irq_desc > > Zoom in: > threadA threadB > for_each_irq_desc(irq, desc) { > get irq_descA which is under freeing > --->preempted by rcu_core()->rcu_do_batch() which releases irq_descA > raw_spin_lock_irqsave(&desc->lock, flags); > //Oops > > And since in the involved code piece, threadA runs in a preemptible > context, and there may be more than one thread at this stage. So the > preempted can happen.
Well, I'm still not sure that this can ever trigger in practice, but I guess the locking can be added for extra safety.
Anyway, the above information should go into the changelog IMO.
That said ->
> > > Signed-off-by: Pingfan Liu <kernelfans@gmail.com> > > > Cc: Thomas Gleixner <tglx@linutronix.de> > > > Cc: "Rafael J. Wysocki" <rafael@kernel.org> > > > To: linux-kernel@vger.kernel.org > > > --- > > > kernel/irq/pm.c | 3 +++ > > > 1 file changed, 3 insertions(+) > > > > > > diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c > > > index ca71123a6130..4b67a4c7de3c 100644 > > > --- a/kernel/irq/pm.c > > > +++ b/kernel/irq/pm.c > > > @@ -133,6 +133,7 @@ void suspend_device_irqs(void) > > > struct irq_desc *desc; > > > int irq; > > > > > > + irq_lock_sparse(); > > > for_each_irq_desc(irq, desc) { > > > unsigned long flags; > > > bool sync; > > > @@ -146,6 +147,7 @@ void suspend_device_irqs(void) > > > if (sync) > > > synchronize_irq(irq);
-> is it entirely safe to call synchronize_irq() under irq_lock_sparse?
> > > } > > > + irq_unlock_sparse(); > > > } > > > EXPORT_SYMBOL_GPL(suspend_device_irqs); > > > > > > @@ -186,6 +188,7 @@ static void resume_irqs(bool want_early) > > > struct irq_desc *desc; > > > int irq; > > > > > > + /* The early resume stage is free of irq_desc release */ > > > for_each_irq_desc(irq, desc) { > > > unsigned long flags; > > > bool is_early = desc->action && > > > -- > > > 2.31.1 > > >
| |