Re: [PATCH 1/2] md/raid5: Remove unnecessary bio_put() in raid5_read_one_chunk()

Paul Menzel
2022-09-05T06:07:29Z

Dear Logan, dear David,

Thank you for the patch.

Am 02.09.22 um 19:16 schrieb Logan Gunthorpe:
> From: David Sloan <david.sloan@eideticom.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@eideticom.com>
> [logang@deltatee.com: minor rewording of commit message]
> Signed-off-by: Logan Gunthorpe <logang@deltatee.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;
> }