From: Jakob Koschel <jakobkoschel@gmail.com>
To: "Christian König" <christian.koenig@amd.com>
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Subject: Re: [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr
Date: Mon, 28 Feb 2022 23:05:26 +0100 [thread overview]
Message-ID: <192A6D7F-E803-47AE-9C7A-267B4E87C856@gmail.com> (raw)
In-Reply-To: <0b65541a-3da7-dc35-690a-0ada75b0adae@amd.com>
> On 28. Feb 2022, at 21:56, Christian König <christian.koenig@amd.com> wrote:
>
>
>
> Am 28.02.22 um 21:42 schrieb James Bottomley:
>> On Mon, 2022-02-28 at 21:07 +0100, Christian König wrote:
>>> Am 28.02.22 um 20:56 schrieb Linus Torvalds:
>>>> On Mon, Feb 28, 2022 at 4:19 AM Christian König
>>>> <christian.koenig@amd.com> wrote:
>>>> [SNIP]
>>>> Anybody have any ideas?
>>> I think we should look at the use cases why code is touching (pos)
>>> after the loop.
>>>
>>> Just from skimming over the patches to change this and experience
>>> with the drivers/subsystems I help to maintain I think the primary
>>> pattern looks something like this:
>>>
>>> list_for_each_entry(entry, head, member) {
>>> if (some_condition_checking(entry))
>>> break;
>>> }
>>> do_something_with(entry);
There are other cases where the list iterator variable is used after the loop
Some examples:
- list_for_each_entry_continue() and list_for_each_entry_from().
- (although very rare) the head is actually of the correct struct type.
(ppc440spe_get_group_entry(): drivers/dma/ppc4xx/adma.c:1436)
- to use pos->list for example for list_add_tail():
(add_static_vm_early(): arch/arm/mm/ioremap.c:107)
If the scope of the list iterator is limited those still need fixing in a different way.
>>
>> Actually, we usually have a check to see if the loop found anything,
>> but in that case it should something like
>>
>> if (list_entry_is_head(entry, head, member)) {
>> return with error;
>> }
>> do_somethin_with(entry);
>>
>> Suffice? The list_entry_is_head() macro is designed to cope with the
>> bogus entry on head problem.
>
> That will work and is also what people already do.
>
> The key problem is that we let people do the same thing over and over again with slightly different implementations.
>
> Out in the wild I've seen at least using a separate variable, using a bool to indicate that something was found and just assuming that the list has an entry.
>
> The last case is bogus and basically what can break badly.
>
> If we would have an unified macro which search for an entry combined with automated reporting on patches to use that macro I think the potential to introduce such issues will already go down massively without auditing tons of existing code.
Having a unified way to do the same thing would indeed be great.
>
> Regards,
> Christian.
>
>>
>> James
>>
>>
>
- Jakob
next prev parent reply other threads:[~2022-02-28 22:06 UTC|newest]
Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-28 11:08 [PATCH 0/6] Remove usage of list iterator past the loop body Jakob Koschel
2022-02-28 11:08 ` [PATCH 1/6] drivers: usb: remove " Jakob Koschel
2022-02-28 11:24 ` Dan Carpenter
2022-02-28 12:03 ` Jakob Koschel
2022-02-28 13:18 ` Dan Carpenter
2022-02-28 18:20 ` Joe Perches
2022-03-01 5:52 ` Dan Carpenter
2022-02-28 11:08 ` [PATCH 2/6] treewide: remove using list iterator after loop body as a ptr Jakob Koschel
2022-02-28 11:20 ` Greg KH
2022-02-28 12:06 ` Jakob Koschel
2022-03-01 17:37 ` Greg KH
2022-02-28 12:19 ` Christian König
2022-02-28 19:56 ` Linus Torvalds
2022-02-28 20:03 ` Linus Torvalds
2022-02-28 20:10 ` Linus Torvalds
2022-02-28 20:14 ` Linus Torvalds
2022-02-28 20:53 ` Segher Boessenkool
2022-02-28 20:16 ` Matthew Wilcox
2022-02-28 20:27 ` Johannes Berg
2022-02-28 20:41 ` Linus Torvalds
2022-02-28 20:37 ` Linus Torvalds
2022-02-28 23:26 ` Matthew Wilcox
2022-03-01 0:45 ` Linus Torvalds
2022-03-01 0:57 ` Linus Torvalds
2022-03-01 18:14 ` Kees Cook
2022-03-01 18:47 ` Linus Torvalds
2022-03-01 19:01 ` Matthew Wilcox
2022-03-01 3:03 ` David Laight
2022-02-28 21:47 ` Jakob Koschel
2022-03-01 0:41 ` Linus Torvalds
2022-03-01 6:32 ` Jakub Kicinski
2022-03-01 11:28 ` Jakob Koschel
2022-03-01 17:36 ` Greg KH
2022-03-01 17:40 ` Jakob Koschel
2022-03-01 17:58 ` Greg KH
2022-03-01 18:21 ` Kees Cook
2022-03-02 9:31 ` Xiaomeng Tong
2022-03-02 14:04 ` David Laight
2022-03-03 2:27 ` Xiaomeng Tong
2022-03-03 4:58 ` David Laight
2022-03-03 7:26 ` Xiaomeng Tong
2022-03-03 9:30 ` David Laight
2022-03-03 12:37 ` Xiaomeng Tong
2022-03-03 12:18 ` [Kgdb-bugreport] " Daniel Thompson
2022-03-04 6:59 ` Xiaomeng Tong
2022-03-03 7:32 ` Jakob Koschel
2022-03-03 8:30 ` Xiaomeng Tong
2022-03-03 8:38 ` Xiaomeng Tong
2022-02-28 20:07 ` Christian König
2022-02-28 20:42 ` James Bottomley
2022-02-28 20:56 ` Christian König
2022-02-28 21:13 ` James Bottomley
2022-03-01 7:03 ` Christian König
2022-02-28 22:05 ` Jakob Koschel [this message]
2022-02-28 21:18 ` Jeffrey Walton
2022-02-28 21:59 ` Mike Rapoport
2022-02-28 22:28 ` James Bottomley
2022-02-28 22:50 ` Barnabás Pőcze
2022-03-01 0:30 ` Segher Boessenkool
2022-03-01 0:54 ` Linus Torvalds
2022-03-01 19:06 ` Linus Torvalds
2022-03-01 19:42 ` Linus Torvalds
2022-03-01 22:58 ` David Laight
2022-03-01 23:03 ` Linus Torvalds
2022-03-01 23:19 ` David Laight
2022-03-01 23:55 ` Linus Torvalds
2022-03-02 9:29 ` Rasmus Villemoes
2022-03-02 20:07 ` Kees Cook
2022-03-02 20:18 ` Linus Torvalds
2022-03-02 20:59 ` Kees Cook
2022-03-03 8:37 ` Dan Carpenter
2022-03-03 10:56 ` Dan Carpenter
2022-03-01 2:15 ` David Laight
2022-02-28 13:13 ` Dan Carpenter
2022-02-28 11:08 ` [PATCH 3/6] treewide: fix incorrect use to determine if list is empty Jakob Koschel
2022-02-28 11:38 ` Dan Carpenter
2022-02-28 11:08 ` [PATCH 4/6] drivers: remove unnecessary use of list iterator variable Jakob Koschel
2022-02-28 11:08 ` [PATCH 5/6] treewide: remove dereference of list iterator after loop body Jakob Koschel
2022-02-28 11:08 ` [PATCH 6/6] treewide: remove check of list iterator against head past the " Jakob Koschel
2022-02-28 11:22 ` Dominique Martinet
2022-02-28 13:12 ` Dan Carpenter
2022-03-01 20:36 ` Linus Torvalds
2022-03-02 17:14 ` [Intel-gfx] " Tvrtko Ursulin
2022-03-07 15:00 ` [PATCH 0/6] Remove usage of list iterator " Dan Carpenter
2022-03-07 15:26 ` David Laight
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