Re: [PATCH v4] block: fix trace completion for chained bio
From: Jens Axboe
Date: Thu Jun 24 2021 - 11:54:16 EST
On 6/24/21 6:30 AM, 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.