lkml.org 
[lkml]   [2023]   [Mar]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] watchdog: avoid usage of iterator after loop
On 3/1/23 14:42, Jakob Koschel wrote:
> 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.
>

Ah, interesting question. Looking into it, I don't think that is a problem.
Just to be sure, I wrote a little coccinelle script to find calls to kfree()
under spinlock_irq() and found several instances.

Guenter

\
 
 \ /
  Last update: 2023-03-27 00:41    [W:0.046 / U:0.520 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site