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Subject[PATCH 4.19 86/99] loop: Push loop_ctl_mutex down into loop_clr_fd()
Date
4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@suse.cz>

commit 7ccd0791d98531df7cd59e92d55e4f063d48a070 upstream.

loop_clr_fd() has a weird locking convention that is expects
loop_ctl_mutex held, releases it on success and keeps it on failure.
Untangle the mess by moving locking of loop_ctl_mutex into
loop_clr_fd().

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/block/loop.c | 49 +++++++++++++++++++++++++++++--------------------
1 file changed, 29 insertions(+), 20 deletions(-)

--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1028,15 +1028,22 @@ loop_init_xfer(struct loop_device *lo, s

static int __loop_clr_fd(struct loop_device *lo)
{
- struct file *filp = lo->lo_backing_file;
+ struct file *filp = NULL;
gfp_t gfp = lo->old_gfp_mask;
struct block_device *bdev = lo->lo_device;
+ int err = 0;

- if (WARN_ON_ONCE(lo->lo_state != Lo_rundown))
- return -ENXIO;
+ mutex_lock(&loop_ctl_mutex);
+ if (WARN_ON_ONCE(lo->lo_state != Lo_rundown)) {
+ err = -ENXIO;
+ goto out_unlock;
+ }

- if (filp == NULL)
- return -EINVAL;
+ filp = lo->lo_backing_file;
+ if (filp == NULL) {
+ err = -EINVAL;
+ goto out_unlock;
+ }

/* freeze request queue during the transition */
blk_mq_freeze_queue(lo->lo_queue);
@@ -1083,6 +1090,7 @@ static int __loop_clr_fd(struct loop_dev
if (!part_shift)
lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
loop_unprepare_queue(lo);
+out_unlock:
mutex_unlock(&loop_ctl_mutex);
/*
* Need not hold loop_ctl_mutex to fput backing file.
@@ -1090,14 +1098,22 @@ static int __loop_clr_fd(struct loop_dev
* lock dependency possibility warning as fput can take
* bd_mutex which is usually taken before loop_ctl_mutex.
*/
- fput(filp);
- return 0;
+ if (filp)
+ fput(filp);
+ return err;
}

static int loop_clr_fd(struct loop_device *lo)
{
- if (lo->lo_state != Lo_bound)
+ int err;
+
+ err = mutex_lock_killable_nested(&loop_ctl_mutex, 1);
+ if (err)
+ return err;
+ if (lo->lo_state != Lo_bound) {
+ mutex_unlock(&loop_ctl_mutex);
return -ENXIO;
+ }
/*
* If we've explicitly asked to tear down the loop device,
* and it has an elevated reference count, set it for auto-teardown when
@@ -1114,6 +1130,7 @@ static int loop_clr_fd(struct loop_devic
return 0;
}
lo->lo_state = Lo_rundown;
+ mutex_unlock(&loop_ctl_mutex);

return __loop_clr_fd(lo);
}
@@ -1448,14 +1465,7 @@ static int lo_ioctl(struct block_device
mutex_unlock(&loop_ctl_mutex);
break;
case LOOP_CLR_FD:
- err = mutex_lock_killable_nested(&loop_ctl_mutex, 1);
- if (err)
- return err;
- /* loop_clr_fd would have unlocked loop_ctl_mutex on success */
- err = loop_clr_fd(lo);
- if (err)
- mutex_unlock(&loop_ctl_mutex);
- break;
+ return loop_clr_fd(lo);
case LOOP_SET_STATUS:
err = -EPERM;
if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN)) {
@@ -1691,7 +1701,6 @@ out:
static void lo_release(struct gendisk *disk, fmode_t mode)
{
struct loop_device *lo;
- int err;

mutex_lock(&loop_ctl_mutex);
lo = disk->private_data;
@@ -1702,13 +1711,13 @@ static void lo_release(struct gendisk *d
if (lo->lo_state != Lo_bound)
goto out_unlock;
lo->lo_state = Lo_rundown;
+ mutex_unlock(&loop_ctl_mutex);
/*
* In autoclear mode, stop the loop thread
* and remove configuration after last close.
*/
- err = __loop_clr_fd(lo);
- if (!err)
- return;
+ __loop_clr_fd(lo);
+ return;
} else if (lo->lo_state == Lo_bound) {
/*
* Otherwise keep thread (if running) and config,

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