linux-kernel - Re: [PATCH] blk-mq: fix alignment mismatch.

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Date:   Tue, 30 Mar 2021 17:26:37 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Nathan Chancellor <nathan@...nel.org>,
        Jian Cai <jiancai@...gle.com>
Cc:     cjdb@...gle.com, manojgupta@...gle.com, llozano@...gle.com,
        clang-built-linux@...glegroups.com, Jens Axboe <axboe@...nel.dk>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] blk-mq: fix alignment mismatch.

On 3/30/21 4:29 PM, Nathan Chancellor wrote:
> Hi Jian,
> 
> On Tue, Mar 30, 2021 at 04:02:49PM -0700, Jian Cai wrote:
>> This fixes the mismatch of alignments between csd and its use as an
>> argument to smp_call_function_single_async, which causes build failure
>> when -Walign-mismatch in Clang is used.
>>
>> Link:
>> http://crrev.com/c/1193732
>>
>> Suggested-by: Guenter Roeck <linux@...ck-us.net>
>> Signed-off-by: Jian Cai <jiancai@...gle.com>
> 
> Thanks for the patch. This is effectively a revert of commit
> 4ccafe032005 ("block: unalign call_single_data in struct request"),
> which I had brought up in this thread:
> 
> https://lore.kernel.org/r/20210310182307.zzcbi5w5jrmveld4@archlinux-ax161/
> 
> This is obviously a correct fix, I am not just sure what the impact to
> 'struct request' will be.
> 

As commit 4ccafe032005 states, it increases the request structure size.
Given the exchange referenced above, I think we'll need to disable
the warning in the block code.

Thanks,
Guenter

> Cheers,
> Nathan
> 
>> ---
>>  include/linux/blkdev.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index bc6bc8383b43..3b92330d95ad 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -231,7 +231,7 @@ struct request {
>>  	unsigned long deadline;
>>  
>>  	union {
>> -		struct __call_single_data csd;
>> +		call_single_data_t csd;
>>  		u64 fifo_time;
>>  	};
>>  
>> -- 
>> 2.31.0.291.g576ba9dcdaf-goog
>>