linux-kernel - Re: [PATCH] slab: remove __alloc_size attribute from __kmalloc_track

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Message-ID: <c237f6d1-4219-0e6d-6aca-9c29d060bb4f@suse.cz>
Date:   Fri, 18 Feb 2022 19:54:14 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable <stable@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Daniel Micay <danielmicay@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <nathan@...nel.org>, linux-mm@...ck.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] slab: remove __alloc_size attribute from
 __kmalloc_track_caller

On 2/18/22 18:57, Greg Kroah-Hartman wrote:
> On Fri, Feb 18, 2022 at 06:14:55PM +0100, Vlastimil Babka wrote:
>> On 2/18/22 14:13, Greg Kroah-Hartman wrote:
>> > Commit c37495d6254c ("slab: add __alloc_size attributes for better
>> > bounds checking") added __alloc_size attributes to a bunch of kmalloc
>> > function prototypes.  Unfortunately the change to __kmalloc_track_caller
>> > seems to cause clang to generate broken code and the first time this is
>> > called when booting, the box will crash.
>> > 
>> > While the compiler problems are being reworked and attempted to be
>> > solved, let's just drop the attribute to solve the issue now.  Once it
>> > is resolved it can be added back.
>> 
>> Could we instead wrap it in some #ifdef that' only true for clang build?
>> That would make the workaround more precise and self-documented. Even
>> better if it can trigger using clang version range and once a fixed
>> clang version is here, it can be updated to stay true for older clangs.
> 
> It's not doing all that much good like this, let's just remove it for
> now until it does actually provide a benifit and not just crash the box :)
> 
> This is only 1 function, that is used in only a very small number of
> callers.  I do not think it will be missed.

Fair enough, added to the slab tree:

https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab.git/log/?h=for-5.17/fixup5

> thanks,
> 
> greg k-h
>