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

From: Guenter Roeck <linux@roeck-us.net>
To: Jian Cai <jiancai@google.com>
Cc: cjdb@google.com, manojgupta@google.com, llozano@google.com,
	clang-built-linux@googlegroups.com, Jens Axboe <axboe@kernel.dk>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] blk-mq: fix alignment mismatch.
Date: Tue, 30 Mar 2021 16:12:39 -0700	[thread overview]
Message-ID: <20210330231239.GA18041@roeck-us.net> (raw)
In-Reply-To: <20210330230249.709221-1-jiancai@google.com>

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

That link does not work. You probably meant
	http://crbug.com/1193732

You'll probably want drop the link and to copy the relevant information
directly into the patch description. Generate the error with an upstream
kernel and cut-and-paste the output here.

For others, the observed error message is:

block/blk-mq.c:622:44: error: passing 8-byte aligned argument to 32-byte
	aligned parameter 2 of 'smp_call_function_single_async' may result
	in an unaligned pointer access [-Werror,-Walign-mismatch]

Thanks,
Guenter

> 
> Suggested-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Jian Cai <jiancai@google.com>
> ---
>  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
> 