Re: [PATCH RESEND v4] loop: fix I/O error on fsync() in detached loop devices

From: Jens Axboe <axboe@kernel.dk>
To: Mauricio Faria de Oliveira <mfo@canonical.com>
Cc: linux-block@vger.kernel.org, ming.lei@redhat.com,
	krisman@collabora.com, eric.desrochers@canonical.com
Subject: Re: [PATCH RESEND v4] loop: fix I/O error on fsync() in detached loop devices
Date: Mon, 22 Feb 2021 08:44:10 -0700	[thread overview]
Message-ID: <8d338b39-af7f-4c03-ea93-b5cad3a91abb@kernel.dk> (raw)
In-Reply-To: <20210222154123.61797-1-mfo@canonical.com>

On 2/22/21 8:41 AM, Mauricio Faria de Oliveira wrote:
> There's an I/O error on fsync() in a detached loop device
> if it has been previously attached.
> 
> The issue is write cache is enabled in the attach path in
> loop_configure() but it isn't disabled in the detach path;
> thus it remains enabled in the block device regardless of
> whether it is attached or not.
> 
> Now fsync() can get an I/O request that will just be failed
> later in loop_queue_rq() as device's state is not 'Lo_bound'.
> 
> So, disable write cache in the detach path.
> 
> Do so based on the queue flag, not the loop device flag for
> read-only (used to enable) as the queue flag can be changed
> via sysfs even on read-only loop devices (e.g., losetup -r.)
> 
> Test-case:
> 
>     # DEV=/dev/loop7
> 
>     # IMG=/tmp/image
>     # truncate --size 1M $IMG
> 
>     # losetup $DEV $IMG
>     # losetup -d $DEV
> 
> Before:
> 
>     # strace -e fsync parted -s $DEV print 2>&1 | grep fsync
>     fsync(3)                                = -1 EIO (Input/output error)
>     Warning: Error fsyncing/closing /dev/loop7: Input/output error
>     [  982.529929] blk_update_request: I/O error, dev loop7, sector 0 op 0x1:(WRITE) flags 0x800 phys_seg 0 prio class 0
> 
> After:
> 
>     # strace -e fsync parted -s $DEV print 2>&1 | grep fsync
>     fsync(3)                                = 0

Applied, thanks.

-- 
Jens Axboe