linux-kernel - Re: [PATCH 1/2] md/raid5: Remove unnecessary bio_put() in raid5_read_one

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Date:   Mon, 5 Sep 2022 08:07:17 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org,
        Song Liu <song@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Guoqing Jiang <guoqing.jiang@...ux.dev>,
        Stephen Bates <sbates@...thlin.com>,
        Martin Oliveira <Martin.Oliveira@...eticom.com>,
        David Sloan <David.Sloan@...eticom.com>
Subject: Re: [PATCH 1/2] md/raid5: Remove unnecessary bio_put() in
 raid5_read_one_chunk()

Dear Logan, dear David,


Thank you for the patch.

Am 02.09.22 um 19:16 schrieb Logan Gunthorpe:
> From: David Sloan <david.sloan@...eticom.com>
> 
> When running chunk-sized reads on disks with badblocks duplicate bio
> free/puts are observed:
> 
>     =============================================================================
>     BUG bio-200 (Not tainted): Object already free
>     -----------------------------------------------------------------------------
>     Allocated in mempool_alloc_slab+0x17/0x20 age=3 cpu=2 pid=7504
>      __slab_alloc.constprop.0+0x5a/0xb0

[…]

> The double free is caused by an unnecessary bio_put() in the
> if(is_badblock(...)) error path in raid5_read_one_chunk().
> 
> The error path was moved ahead of bio_alloc_clone() in c82aa1b76787c
> ("md/raid5: move checking badblock before clone bio in
> raid5_read_one_chunk"). The previous code checked and freed align_bio
> which required a bio_put. After he move that is no longer needed as

*t*he move

> raid_bio is returned to the control of the common io path which
> performs its own endio resulting in a double free on bad device blocks.
> 
> Fixes: c82aa1b76787c ("md/raid5: move checking badblock before clone bio in raid5_read_one_chunk")

This commit was added to Linux in v5.14-rc1, so it’s not a recent commit 
– or I misunderstood the cover letter.


Kind regards,

Paul


> Signed-off-by: David Sloan <david.sloan@...eticom.com>
> [logang@...tatee.com: minor rewording of commit message]
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>   drivers/md/raid5.c | 1 -
>   1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 4e6d865a6456..734f92e75f85 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -5538,7 +5538,6 @@ static int raid5_read_one_chunk(struct mddev *mddev, struct bio *raid_bio)
>   
>   	if (is_badblock(rdev, sector, bio_sectors(raid_bio), &first_bad,
>   			&bad_sectors)) {
> -		bio_put(raid_bio);
>   		rdev_dec_pending(rdev, mddev);
>   		return 0;
>   	}