From: Linus Torvalds <torvalds@linux-foundation.org>
To: "Christian König" <christian.koenig@amd.com>
Cc: Jakob Koschel <jakobkoschel@gmail.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 12:03:34 -0800 [thread overview]
Message-ID: <CAHk-=wj8fkosQ7=bps5K+DDazBXk=ypfn49A0sEq+7-nZnyfXA@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wgQps58DPEOe4y5cTh5oE9EdNTWRLXzgMiETc+mFX7jzw@mail.gmail.com>
On Mon, Feb 28, 2022 at 11:56 AM Linus Torvalds
<torvalds@linux-foundation.org> 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.
Side note: we do need *some* way to do it.
Because if we make that change, and only set it to another pointer
when not the head, then we very much change the semantics of
"list_for_each_head()". The "list was empty" case would now exit with
'pos' not set at all (or set to NULL if we add that). Or it would be
set to the last entry.
And regardless, that means that all the
if (pos == head)
kinds of checks after the loop would be fundamentally broken.
Darn. I really hoped for (and naively expected) that we could actually
have the compiler warn about the use-after-loop case. That whole
"compiler will now complain about bad use" was integral to my clever
plan to use the C99 feature of declaring the iterator inside the loop.
But my "clever plan" was apparently some ACME-level Wile E. Coyote sh*t.
Darn.
Linus
next prev parent reply other threads:[~2022-02-28 20:04 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 [this message]
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
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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