[Crash-utility] [PATCH v2] Handle blk_mq_ctx member changes for kernels v5.16-rc1~75^2~44

[HAGIO KAZUHITO(萩尾 一仁)]

Hi Lianbo,

thanks for the update,

-----Original Message-----
> Subject: [PATCH v2] Handle blk_mq_ctx member changes for kernels v5.16-rc1~75^2~44

only "5.16-rc1" is fine, as we have the commit id below.

> Kernel commit <9a14d6ce4135> ("block: remove debugfs blk_mq_ctx
> dispatched/merged/completed attributes") removed the member
> rq_dispatched and rq_completed from struct blk_mq_ctx. Without
> this patch, crash will fail with the following error:
> 
> crash> dev -d
> MAJOR GENDISK            NAME       REQUEST_QUEUE      TOTAL ASYNC  SYNC
> 
> dev: invalid structure member offset: blk_mq_ctx_rq_dispatched
>      FILE: dev.c  LINE: 4229  FUNCTION: get_one_mctx_diskio()
> 
> Signed-off-by: Lianbo Jiang <lijiang at redhat.com>
> ---
> change since v1:
> [1] display prompt information "(not supported)" instead of the
> statistical result if kernel does not support it
> 
>  dev.c | 56 ++++++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 38 insertions(+), 18 deletions(-)
> 
> diff --git a/dev.c b/dev.c
> index effe789f38d8..c5e38e1c5376 100644
> --- a/dev.c
> +++ b/dev.c
> @@ -4246,6 +4246,10 @@ get_mq_diskio(unsigned long q, unsigned long *mq_count)
>  	unsigned long mctx_addr;
>  	struct diskio tmp;
> 
> +	if (!MEMBER_EXISTS("blk_mq_ctx", "rq_dispatched") &&
> +		!MEMBER_EXISTS("blk_mq_ctx", "rq_completed"))
> +		return;
> +

It's better to use INVALID_MEMBER() here, because they are in the offset_table and
it doesn't call gdb function.  And, both of them should be gone on 5.16 and later,
but let's use 'or' for safe:

	if (INVALID_MEMBER(blk_mq_ctx_rq_dispatched) ||
	    INVALID_MEMBER(blk_mq_ctx_rq_completed))
		return;

>  	memset(&tmp, 0x00, sizeof(struct diskio));
> 
>  	readmem(q + OFFSET(request_queue_queue_ctx), KVADDR, &queue_ctx,
> @@ -4475,24 +4479,40 @@ display_one_diskio(struct iter *i, unsigned long gendisk, ulong flags)
>  		&& (io.read + io.write == 0))
>  		return;
> 
> -	fprintf(fp, "%s%s%s  %s%s%s%s  %s%5d%s%s%s%s%s",
> -		mkstring(buf0, 5, RJUST|INT_DEC, (char *)(unsigned long)major),
> -		space(MINSPACE),
> -		mkstring(buf1, VADDR_PRLEN, LJUST|LONG_HEX, (char *)gendisk),
> -		space(MINSPACE),
> -		mkstring(buf2, 10, LJUST, disk_name),
> -		space(MINSPACE),
> -		mkstring(buf3, VADDR_PRLEN <= 11 ? 11 : VADDR_PRLEN,
> -			 LJUST|LONG_HEX, (char *)queue_addr),
> -		space(MINSPACE),
> -		io.read + io.write,
> -		space(MINSPACE),
> -		mkstring(buf4, 5, RJUST|INT_DEC,
> -			(char *)(unsigned long)io.read),
> -		space(MINSPACE),
> -		mkstring(buf5, 5, RJUST|INT_DEC,
> -			(char *)(unsigned long)io.write),
> -		space(MINSPACE));
> +	if (!MEMBER_EXISTS("blk_mq_ctx", "rq_dispatched") &&
> +		!MEMBER_EXISTS("blk_mq_ctx", "rq_completed"))

Same as above.

And this stops displaying the statistics of all devices on 5.16 kernel.
I think that we can stop only mq devices, so how about this?

	if (use_mq_interface(queue_addr) &&
	    (INVALID_MEMBER(blk_mq_ctx_rq_dispatched) ||
	     INVALID_MEMBER(blk_mq_ctx_rq_completed)))

With this, on a 5.16-rc2 kernel:

crash-dev> dev -d
MAJOR GENDISK            NAME       REQUEST_QUEUE      TOTAL ASYNC  SYNC 
    8 ffff92bbd102e400   sdb        ffff92bbf04e3678     (not supported) 
    8 ffff92bbd1014400   sdc        ffff92bbf04e26e8     (not supported) 
    8 ffff92bbc9bff200   sdd        ffff92bbf04e07c8     (not supported) 
    8 ffff92bbd9676200   sda        ffff92bbf04e0000     (not supported) 
   11 ffff92c347da5e00   sr0        ffff92bbd9c3e528     (not supported) 
  253 ffff92bbca726e00   dm-0       ffff92bbcad7dd60       0     0     0 
  253 ffff92bbe03f1000   dm-1       ffff92bbe1d587c8       0     0     0 
  253 ffff92bbe02fa800   dm-2       ffff92bc01b11f20       0     0     0 

where dm-X devices don't use mq interface.

I've modified the patch and attached, you can merge it if you are OK.

Thanks,
Kazu

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