From: Christoph Hellwig <hch@lst.de>
To: axboe@kernel.dk
Cc: ming.lei@redhat.com, pasha.tatashin@soleen.com,
linux-block@vger.kernel.org,
Colin Ian King <colin.king@canonical.com>
Subject: [PATCH] block: loop: fix deadlock between open and remove
Date: Sat, 5 Jun 2021 17:09:50 +0300 [thread overview]
Message-ID: <20210605140950.5800-1-hch@lst.de> (raw)
Commit c76f48eb5c08 ("block: take bd_mutex around delete_partitions in
del_gendisk") adds disk->part0->bd_mutex in del_gendisk(), this way
causes the following AB/BA deadlock between removing loop and opening
loop:
1) loop_control_ioctl(LOOP_CTL_REMOVE)
-> mutex_lock(&loop_ctl_mutex)
-> del_gendisk
-> mutex_lock(&disk->part0->bd_mutex)
2) blkdev_get_by_dev
-> mutex_lock(&disk->part0->bd_mutex)
-> lo_open
-> mutex_lock(&loop_ctl_mutex)
Add a new Lo_deleting state to remove the need for clearing
->private_data and thus holding loop_ctl_mutex in the ioctl
LOOP_CTL_REMOVE path.
Based on an analysis and earlier patch from
Ming Lei <ming.lei@redhat.com>.
Reported-by: Colin Ian King <colin.king@canonical.com>
Fixes: c76f48eb5c08 ("block: take bd_mutex around delete_partitions in del_gendisk")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
drivers/block/loop.c | 25 +++++++------------------
drivers/block/loop.h | 1 +
2 files changed, 8 insertions(+), 18 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index d58d68f3c7cd..76e12f3482a9 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1879,29 +1879,18 @@ static int lo_compat_ioctl(struct block_device *bdev, fmode_t mode,
static int lo_open(struct block_device *bdev, fmode_t mode)
{
- struct loop_device *lo;
+ struct loop_device *lo = bdev->bd_disk->private_data;
int err;
- /*
- * take loop_ctl_mutex to protect lo pointer from race with
- * loop_control_ioctl(LOOP_CTL_REMOVE), however, to reduce contention
- * release it prior to updating lo->lo_refcnt.
- */
- err = mutex_lock_killable(&loop_ctl_mutex);
- if (err)
- return err;
- lo = bdev->bd_disk->private_data;
- if (!lo) {
- mutex_unlock(&loop_ctl_mutex);
- return -ENXIO;
- }
err = mutex_lock_killable(&lo->lo_mutex);
- mutex_unlock(&loop_ctl_mutex);
if (err)
return err;
- atomic_inc(&lo->lo_refcnt);
+ if (lo->lo_state == Lo_deleting)
+ err = -ENXIO;
+ else
+ atomic_inc(&lo->lo_refcnt);
mutex_unlock(&lo->lo_mutex);
- return 0;
+ return err;
}
static void lo_release(struct gendisk *disk, fmode_t mode)
@@ -2285,7 +2274,7 @@ static long loop_control_ioctl(struct file *file, unsigned int cmd,
mutex_unlock(&lo->lo_mutex);
break;
}
- lo->lo_disk->private_data = NULL;
+ lo->lo_state = Lo_deleting;
mutex_unlock(&lo->lo_mutex);
idr_remove(&loop_index_idr, lo->lo_number);
loop_remove(lo);
diff --git a/drivers/block/loop.h b/drivers/block/loop.h
index a3c04f310672..5beb959b94d3 100644
--- a/drivers/block/loop.h
+++ b/drivers/block/loop.h
@@ -22,6 +22,7 @@ enum {
Lo_unbound,
Lo_bound,
Lo_rundown,
+ Lo_deleting,
};
struct loop_func_table;
--
2.30.2
next reply other threads:[~2021-06-05 14:09 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-05 14:09 Christoph Hellwig [this message]
2021-06-05 15:00 ` [PATCH] block: loop: fix deadlock between open and remove Colin Ian King
2021-06-07 0:11 ` Ming Lei
2021-06-11 17:51 ` Jens Axboe
-- strict thread matches above, loose matches on Subject: below --
2021-06-04 0:04 Ming Lei
2021-06-04 6:57 ` Christoph Hellwig
2021-06-04 8:56 ` Ming Lei
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