From: Tom Rix <trix@redhat.com>
To: Zheng Zengkai <zhengzengkai@huawei.com>,
Randy Dunlap <rdunlap@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Howells <dhowells@redhat.com>,
Hulk Robot <hulkci@huawei.com>,
linux-afs@lists.infradead.org,
Marc Dionne <marc.dionne@auristor.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] afs: fix no return statement in function returning non-void
Date: Wed, 16 Jun 2021 05:56:39 -0700 [thread overview]
Message-ID: <200ea6f7-0182-9da1-734c-c49102663ccc@redhat.com> (raw)
In-Reply-To: <051421e0-afe8-c6ca-95cd-4dc8cd20a43e@huawei.com>
On 6/15/21 8:15 PM, Zheng Zengkai wrote:
> Oops, Sorry for the late reply and missing the compilation details.
>
>> On 6/15/21 5:32 PM, Linus Torvalds wrote:
>>> On Tue, Jun 15, 2021 at 4:58 PM Randy Dunlap <rdunlap@infradead.org>
>>> wrote:
>>>> Some implementations of BUG() are macros, not functions,
>>> Not "some", I think. Most.
>>>
>>>> so "unreachable" is not applicable AFAIK.
>>> Sure it is. One common pattern is the x86 one:
>>>
>>> #define BUG() \
>>> do { \
>>> instrumentation_begin(); \
>>> _BUG_FLAGS(ASM_UD2, 0); \
>>> unreachable(); \
>>> } while (0)
>> duh.
>>
>>> and that "unreachable()" is exactly what I'm talking about.
>>>
>>> So I repeat: what completely broken compiler / config / architecture
>>> is it that needs that "return 0" after a BUG() statement?
>> I have seen it on ia64 -- most likely GCC 9.3.0, but I'll have to
>> double check that.
>
> Actually we build the kernel with the following compiler, config and
> architecture :
>
> powerpc64-linux-gnu-gcc --version
> powerpc64-linux-gnu-gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0
> Copyright (C) 2019 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions. There is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
> PURPOSE.
>
> CONFIG_AFS_FS=y
> # CONFIG_AFS_DEBUG is not set
> CONFIG_AFS_DEBUG_CURSOR=y
>
> make ARCH=powerpc CROSS_COMPILE=powerpc64-linux-gnu- -j64
>
> ...
>
> fs/afs/dir.c: In function ‘afs_dir_set_page_dirty’:
> fs/afs/dir.c:51:1: error: no return statement in function returning
> non-void [-Werror=return-type]
> 51 | }
> | ^
> cc1: some warnings being treated as errors
>
powerpc64 gcc 10.3.1 is what I used to find this problem.
A fix is to use the __noreturn attribute on this function and not add a
return like this
-static int afs_dir_set_page_dirty(struct page *page)
+static int __noreturn afs_dir_set_page_dirty(struct page *page)
and to the set of ~300 similar functions in these files.
$ grep -r -P "^\tBUG\(\)" .
If folks are ok with this, I'll get that set started.
Tom
>>> Because that environment is broken, and the warning is bogus and wrong.
>>>
>>> It might not be the compiler. It might be some architecture that does
>>> this wrong. It might be some very particular configuration that does
>>> something bad and makes the "unreachable()" not work (or not exist).
>>>
>>> But *that* is the bug that should be fixed. Not adding a pointless and
>>> incorrect line that makes no sense, just to hide the real bug.
>> .
>>
>
next prev parent reply other threads:[~2021-06-16 12:56 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-15 11:55 [PATCH] afs: fix no return statement in function returning non-void David Howells
2021-06-15 12:03 ` David Howells
2021-06-15 14:49 ` Linus Torvalds
2021-06-15 23:58 ` Randy Dunlap
2021-06-16 0:32 ` Linus Torvalds
2021-06-16 1:38 ` Randy Dunlap
2021-06-16 2:19 ` Randy Dunlap
2021-06-16 3:15 ` Zheng Zengkai
2021-06-16 12:56 ` Tom Rix [this message]
2021-06-16 14:34 ` Linus Torvalds
2021-06-16 16:22 ` Tom Rix
2021-06-16 16:29 ` Linus Torvalds
2021-06-18 15:23 ` Arnd Bergmann
2021-06-16 13:41 ` David Howells
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