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SubjectRe: [PATCH] watchdog: avoid usage of iterator after loop
On 23/03/01 10:31AM, Guenter Roeck wrote:
> On 3/1/23 09:17, Jakob Koschel wrote:
> > If potentially no valid element is found, 'p' would contain an invalid
> > pointer past the iterator loop. To ensure 'p' is valid under any
> > circumstances, the kfree() should be within the loop body.
> >
> > Additionally, Linus proposed to avoid any use of the list iterator
> > variable after the loop, in the attempt to move the list iterator
> > variable declaration into the marcro to avoid any potential misuse after
>
> macro
>
> > the loop [1].
> >
> > Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
> > Signed-off-by: Jakob Koschel <jkl820.git@gmail.com>
> > ---
> > drivers/watchdog/watchdog_pretimeout.c | 6 +++---
> > 1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/watchdog/watchdog_pretimeout.c b/drivers/watchdog/watchdog_pretimeout.c
> > index 376a495ab80c..d8c78696eaf5 100644
> > --- a/drivers/watchdog/watchdog_pretimeout.c
> > +++ b/drivers/watchdog/watchdog_pretimeout.c
> > @@ -207,10 +207,10 @@ void watchdog_unregister_pretimeout(struct watchdog_device *wdd)
> > list_for_each_entry_safe(p, t, &pretimeout_list, entry) {
> > if (p->wdd == wdd) {
> > list_del(&p->entry);
> > - break;
> > + spin_unlock_irq(&pretimeout_lock);
> > + kfree(p);
> > + return;
>
> Please just make it
> kfree(p);
> break;
>
> There is no need to drop the spinlock here and/or to return
> directly.

Ok great, I'll fix that in v2. I wasn't sure if something breaks if 'p' is released if the spinlock is still hold.

~ jakob

>
> Thanks,
> Guenter
>
> > }
> > }
> > spin_unlock_irq(&pretimeout_lock);
> > -
> > - kfree(p);
> > }
> >
> > ---
> > base-commit: c0927a7a5391f7d8e593e5e50ead7505a23cadf9
> > change-id: 20230301-watchdog-avoid-iter-after-loop-a197bf201435
> >
> > Best regards,
>

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