linux-kernel - Re: linux-next: Tree for Sep 12 (bcachefs, objtool)

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Message-ID: <28c68588-401e-4207-8b83-f68761f0a137@infradead.org>
Date:   Wed, 13 Sep 2023 14:39:51 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kent Overstreet <kent.overstreet@...ux.dev>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: linux-next: Tree for Sep 12 (bcachefs, objtool)



On 9/13/23 14:08, Josh Poimboeuf wrote:
> On Tue, Sep 12, 2023 at 04:36:55PM -0700, Randy Dunlap wrote:
>>
>>
>> On 9/11/23 22:26, Stephen Rothwell wrote:
>>> Hi all,
>>>
>>> Changes since 20230911:
>>>
>>> New tree: bcachefs
>>>
>>> The bcachefs tree gained a semantic conflict against Linus' tree for
>>> which I applied a patch.
>>>
>>> The wireless-next tree gaind a conflict against the wireless tree.
>>>
>>> Non-merge commits (relative to Linus' tree): 4095
>>>  1552 files changed, 346893 insertions(+), 22945 deletions(-)
>>>
>>> ----------------------------------------------------------------------------
>>
>> on x86_64:
>>
>> vmlinux.o: warning: objtool: bch2_dev_buckets_reserved.part.0() is missing an ELF size annotation
> 
> Here ya go:
> 
> ---8<---
> 
> From: Josh Poimboeuf <jpoimboe@...nel.org>
> Subject: [PATCH] bcachefs: Remove undefined behavior in bch2_dev_buckets_reserved()
> 
> In general it's a good idea to avoid using bare unreachable() because it
> introduces undefined behavior in compiled code.  In this case it even
> confuses GCC into emitting an empty unused
> bch2_dev_buckets_reserved.part.0() function.
> 
> Use BUG() instead, which is nice and defined.  While in theory it should
> never trigger, if something were to go awry and the BCH_WATERMARK_NR
> case were to actually hit, the failure mode is much more robust.
> 
> Fixes the following warnings:
> 
>   vmlinux.o: warning: objtool: bch2_bucket_alloc_trans() falls through to next function bch2_reset_alloc_cursors()
>   vmlinux.o: warning: objtool: bch2_dev_buckets_reserved.part.0() is missing an ELF size annotation
> 
> Reported-by: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>

Tested-by: Randy Dunlap <rdunlap@...radead.org>
Reviewed-by: Randy Dunlap <rdunlap@...radead.org>

Thanks, Josh.


> ---
>  fs/bcachefs/buckets.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/bcachefs/buckets.h b/fs/bcachefs/buckets.h
> index f192809f50cf..0eff05c79c65 100644
> --- a/fs/bcachefs/buckets.h
> +++ b/fs/bcachefs/buckets.h
> @@ -180,7 +180,7 @@ static inline u64 bch2_dev_buckets_reserved(struct bch_dev *ca, enum bch_waterma
>  
>  	switch (watermark) {
>  	case BCH_WATERMARK_NR:
> -		unreachable();
> +		BUG();
>  	case BCH_WATERMARK_stripe:
>  		reserved += ca->mi.nbuckets >> 6;
>  		fallthrough;

-- 
~Randy