From: Jan Kara <jack@suse.cz>
To: Dongli Zhang <dongli.zhang@oracle.com>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
axboe@kernel.dk, jack@suse.cz
Subject: Re: [PATCH 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part()
Date: Thu, 21 Feb 2019 12:30:05 +0100 [thread overview]
Message-ID: <20190221113005.GF27474@quack2.suse.cz> (raw)
In-Reply-To: <1550722655-15102-3-git-send-email-dongli.zhang@oracle.com>
On Thu 21-02-19 12:17:35, 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
Can you perhaps write a blktest for this? Thanks!
> 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@oracle.com>
> ---
> drivers/block/loop.c | 15 ++++++++++++---
> 1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 7908673..736e55b 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -1034,6 +1034,15 @@ loop_init_xfer(struct loop_device *lo, struct loop_func_table *xfer,
> return err;
> }
>
> +static void loop_disable_partscan(struct loop_device *lo)
> +{
> + mutex_lock(&loop_ctl_mutex);
> + lo->lo_flags = 0;
> + if (!part_shift)
> + lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
> + mutex_unlock(&loop_ctl_mutex);
> +}
> +
> static int __loop_clr_fd(struct loop_device *lo, bool release)
> {
> struct file *filp = NULL;
> @@ -1096,9 +1105,6 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
>
> partscan = lo->lo_flags & LO_FLAGS_PARTSCAN && bdev;
> lo_number = lo->lo_number;
> - lo->lo_flags = 0;
> - if (!part_shift)
> - lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
> loop_unprepare_queue(lo);
> out_unlock:
> mutex_unlock(&loop_ctl_mutex);
> @@ -1121,6 +1127,9 @@ static int __loop_clr_fd(struct loop_device *lo, bool release)
> /* Device is gone, no point in returning error */
> err = 0;
> }
> +
> + loop_disable_partscan(lo);
> +
> /*
> * Need not hold loop_ctl_mutex to fput backing file.
> * Calling fput holding loop_ctl_mutex triggers a circular
So I don't think this change is actually correct. The problem is that once
lo->lo_state is set to Lo_unbound and loop_ctl_mutex is unlocked, the loop
device structure can be reused for a new device (bound to a new file). So
you cannot safely manipulate flags on lo->lo_disk anymore. But I think we
can just move the setting of lo->lo_state to Lo_unbound after partscan has
finished as well. There cannot be anybody else entering __loop_clr_fd() as
lo->lo_backing_file is already cleared and Lo_rundown state protects us
from all the other places trying to change the 'lo' device (please make
this last sentence into a comment in the code explaining why setting
lo->lo_state so late is fine). Thanks!
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2019-02-21 11:30 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-21 4:17 [PATCH 0/2] loop: fix two issues introduced by prior commit Dongli Zhang
2019-02-21 4:17 ` [PATCH 1/2] loop: do not print warn message if partition scan is successful Dongli Zhang
2019-02-21 11:01 ` Jan Kara
2019-02-21 4:17 ` [PATCH 2/2] loop: set GENHD_FL_NO_PART_SCAN after blkdev_reread_part() Dongli Zhang
2019-02-21 11:30 ` Jan Kara [this message]
2019-02-21 15:25 ` Dongli Zhang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190221113005.GF27474@quack2.suse.cz \
--to=jack@suse.cz \
--cc=axboe@kernel.dk \
--cc=dongli.zhang@oracle.com \
--cc=linux-block@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).