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

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Message-ID: <ff63b647-0c0b-e7c7-0daf-499dc358e0dd@kernel.dk>
Date:   Thu, 24 Jun 2021 09:54:12 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     edwardh <edwardh@...ology.com>, neilb@...e.com, hch@...radead.org
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        s3t@...ology.com, bingjingc@...ology.com, cccheng@...ology.com,
        Wade Liang <wadel@...ology.com>
Subject: Re: [PATCH v4] block: fix trace completion for chained bio

On 6/24/21 6:30 AM, edwardh wrote:
> From: Edward Hsieh <edwardh@...ology.com>
> 
> 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.

Applied, thanks.

-- 
Jens Axboe