linux-kernel - Re: [PATCH v2 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread

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Date:   Fri, 22 Feb 2019 12:47:19 +0100
From:   Jan Kara <jack@...e.cz>
To:     Dongli Zhang <dongli.zhang@...cle.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        axboe@...nel.dk, jack@...e.cz
Subject: Re: [PATCH v2 2/2] loop: set GENHD_FL_NO_PART_SCAN after
 blkdev_reread_part()

On Thu 21-02-19 23:33:43, Dongli Zhang wrote:
> Commit 0da03cab87e6
> ("loop: Fix deadlock when calling blkdev_reread_part()") moves
> blkdev_reread_part() out of the loop_ctl_mutex. However,
> GENHD_FL_NO_PART_SCAN is set before __blkdev_reread_part(). As a result,
> __blkdev_reread_part() will fail the check of GENHD_FL_NO_PART_SCAN and
> will not rescan the loop device to delete all partitions.
> 
> Below are steps to reproduce the issue:
> 
> step1 # dd if=/dev/zero of=tmp.raw bs=1M count=100
> step2 # losetup -P /dev/loop0 tmp.raw
> step3 # parted /dev/loop0 mklabel gpt
> step4 # parted -a none -s /dev/loop0 mkpart primary 64s 1
> step5 # losetup -d /dev/loop0
> 
> Step5 will not be able to delete /dev/loop0p1 (introduced by step4) and
> there is below kernel warning message:
> 
> [  464.414043] __loop_clr_fd: partition scan of loop0 failed (rc=-22)
> 
> This patch sets GENHD_FL_NO_PART_SCAN after blkdev_reread_part().
> 
> Fixes: 0da03cab87e6 ("loop: Fix deadlock when calling blkdev_reread_part()")
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
> ---
> Changed since v1:
>   * move the setting of lo->lo_state to Lo_unbound after partscan has finished as well
>     (suggested by Jan Kara)
> 
>  drivers/block/loop.c | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)

Thanks the patch looks good! Just one nit below:

> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 7908673..a13f5dc 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1034,6 +1034,16 @@ loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
>  	return err;
>  }
>  
> +static void loop_disable_partscan(struct loop_device *lo)
> +{

I don't think there's any benefit in having this small function with a single
caller and furthermore with the subtle sideeffect that it changes lo_state.
So I'd just put the code inline in __loop_clr_fd(). With that you can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR