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

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Date:   Tue, 30 Mar 2021 16:29:46 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Jian Cai <jiancai@...gle.com>
Cc:     cjdb@...gle.com, manojgupta@...gle.com, llozano@...gle.com,
        clang-built-linux@...glegroups.com,
        Guenter Roeck <linux@...ck-us.net>,
        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.

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.

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
>