From: Segher Boessenkool <segher@kernel.crashing.org>
To: James Bottomley <James.Bottomley@HansenPartnership.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 18:30:59 -0600 [thread overview]
Message-ID: <20220301003059.GE614@gate.crashing.org> (raw)
In-Reply-To: <73fa82a20910c06784be2352a655acc59e9942ea.camel@HansenPartnership.com>
On Mon, Feb 28, 2022 at 05:28:58PM -0500, James Bottomley wrote:
> On Mon, 2022-02-28 at 23:59 +0200, Mike Rapoport wrote:
> >
> > On February 28, 2022 10:42:53 PM GMT+02:00, James Bottomley <
> > James.Bottomley@HansenPartnership.com> wrote:
> > > On Mon, 2022-02-28 at 21:07 +0100, Christian König wrote:
> [...]
> > > > > I do wish we could actually poison the 'pos' value after the
> > > > > loop somehow - but clearly the "might be uninitialized" I was
> > > > > hoping for isn't the way to do it.
> > > > >
> > > > > 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);
> > >
> > > 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.
> >
> > Won't suffice because the end goal of this work is to limit scope of
> > entry only to loop. Hence the need for additional variable.
>
> Well, yes, but my objection is more to the size of churn than the
> desire to do loop local. I'm not even sure loop local is possible,
> because it's always annoyed me that for (int i = 0; ... in C++ defines
> i in the outer scope not the loop scope, which is why I never use it.
In C its scope is the rest of the declaration and the entire loop, not
anything after it. This was the same in C++98 already, btw (but in
pre-standard versions of C++ things were like you remember, yes, and it
was painful).
Segher
next prev parent reply other threads:[~2022-03-01 0:47 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
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 [this message]
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 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
2022-03-07 19:15 ` Linus Torvalds
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