Re: [PATCH v4] block: fix trace completion for chained bio

[Christoph Hellwig]

On Thu, Jun 24, 2021 at 08:30:30PM +0800, edwardh wrote:
> From: Edward Hsieh <edwardh@xxxxxxxxxxxx>
> 
> For chained bio, trace_block_bio_complete in bio_endio is currently called
> only by the parent bio once upon all chained bio completed.
> However, the sector and size for the parent bio are modified in bio_split.
> Therefore, the size and sector of the complete events might not match the
> queue events in blktrace.
> 
> The original fix of bio completion trace <fbbaf700e7b1> ("block: trace
> completion of all bios.") wants multiple complete events to correspond
> to one queue event but missed this.
> 
> The issue can be reproduced by md/raid5 read with bio cross chunks.
> 
> To fix, move trace completion into the loop for every chained bio to call.
> 
> Fixes: fbbaf700e7b1 ("block: trace completion of all bios.")
> Reviewed-by: Wade Liang <wadel@xxxxxxxxxxxx>
> Reviewed-by: BingJing Chang <bingjingc@xxxxxxxxxxxx>
> Signed-off-by: Edward Hsieh <edwardh@xxxxxxxxxxxx>

Looks good,

Reviewed-by: Christoph Hellwig <hch@xxxxxx>