lkml.org 
[lkml]   [2022]   [Apr]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [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
> > >

\
 
 \ /
  Last update: 2022-04-21 12:58    [W:0.081 / U:0.184 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site