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loop: make autoclear operation asynchronous
syzbot is reporting circular locking problem at __loop_clr_fd() [1], for
commit 87579e9b7d
("loop: use worker per cgroup instead of kworker")
is calling destroy_workqueue() with disk->open_mutex held.
This circular dependency cannot be broken unless we call __loop_clr_fd()
without holding disk->open_mutex. Therefore, defer __loop_clr_fd() from
lo_release() to a WQ context.
Link: https://syzkaller.appspot.com/bug?extid=643e4ce4b6ad1347d372 [1]
Reported-by: syzbot <syzbot+643e4ce4b6ad1347d372@syzkaller.appspotmail.com>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Cc: Jan Kara <jack@suse.cz>
Tested-by: syzbot+643e4ce4b6ad1347d372@syzkaller.appspotmail.com
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/1ed7df28-ebd6-71fb-70e5-1c2972e05ddb@i-love.sakura.ne.jp
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
parent
c5eafd790e
commit
322c4293ec
2 changed files with 37 additions and 29 deletions
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@ -1082,7 +1082,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
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return error;
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}
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static void __loop_clr_fd(struct loop_device *lo, bool release)
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static void __loop_clr_fd(struct loop_device *lo)
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{
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struct file *filp;
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gfp_t gfp = lo->old_gfp_mask;
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@ -1144,8 +1144,6 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
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/* let user-space know about this change */
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kobject_uevent(&disk_to_dev(lo->lo_disk)->kobj, KOBJ_CHANGE);
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mapping_set_gfp_mask(filp->f_mapping, gfp);
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/* This is safe: open() is still holding a reference. */
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module_put(THIS_MODULE);
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blk_mq_unfreeze_queue(lo->lo_queue);
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disk_force_media_change(lo->lo_disk, DISK_EVENT_MEDIA_CHANGE);
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@ -1153,44 +1151,52 @@ static void __loop_clr_fd(struct loop_device *lo, bool release)
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if (lo->lo_flags & LO_FLAGS_PARTSCAN) {
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int err;
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/*
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* open_mutex has been held already in release path, so don't
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* acquire it if this function is called in such case.
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*
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* If the reread partition isn't from release path, lo_refcnt
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* must be at least one and it can only become zero when the
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* current holder is released.
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*/
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if (!release)
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mutex_lock(&lo->lo_disk->open_mutex);
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mutex_lock(&lo->lo_disk->open_mutex);
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err = bdev_disk_changed(lo->lo_disk, false);
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if (!release)
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mutex_unlock(&lo->lo_disk->open_mutex);
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mutex_unlock(&lo->lo_disk->open_mutex);
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if (err)
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pr_warn("%s: partition scan of loop%d failed (rc=%d)\n",
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__func__, lo->lo_number, err);
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/* Device is gone, no point in returning error */
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}
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/*
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* lo->lo_state is set to Lo_unbound here after above partscan has
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* finished. There cannot be anybody else entering __loop_clr_fd() as
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* Lo_rundown state protects us from all the other places trying to
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* change the 'lo' device.
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*/
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lo->lo_flags = 0;
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if (!part_shift)
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lo->lo_disk->flags |= GENHD_FL_NO_PART;
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fput(filp);
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}
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static void loop_rundown_completed(struct loop_device *lo)
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{
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mutex_lock(&lo->lo_mutex);
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lo->lo_state = Lo_unbound;
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mutex_unlock(&lo->lo_mutex);
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module_put(THIS_MODULE);
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}
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/*
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* Need not hold lo_mutex to fput backing file. Calling fput holding
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* lo_mutex triggers a circular lock dependency possibility warning as
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* fput can take open_mutex which is usually taken before lo_mutex.
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*/
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fput(filp);
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static void loop_rundown_workfn(struct work_struct *work)
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{
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struct loop_device *lo = container_of(work, struct loop_device,
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rundown_work);
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struct block_device *bdev = lo->lo_device;
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struct gendisk *disk = lo->lo_disk;
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__loop_clr_fd(lo);
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kobject_put(&bdev->bd_device.kobj);
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module_put(disk->fops->owner);
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loop_rundown_completed(lo);
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}
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static void loop_schedule_rundown(struct loop_device *lo)
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{
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struct block_device *bdev = lo->lo_device;
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struct gendisk *disk = lo->lo_disk;
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__module_get(disk->fops->owner);
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kobject_get(&bdev->bd_device.kobj);
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INIT_WORK(&lo->rundown_work, loop_rundown_workfn);
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queue_work(system_long_wq, &lo->rundown_work);
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}
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static int loop_clr_fd(struct loop_device *lo)
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@ -1222,7 +1228,8 @@ static int loop_clr_fd(struct loop_device *lo)
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lo->lo_state = Lo_rundown;
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mutex_unlock(&lo->lo_mutex);
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__loop_clr_fd(lo, false);
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__loop_clr_fd(lo);
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loop_rundown_completed(lo);
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return 0;
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}
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@ -1747,7 +1754,7 @@ static void lo_release(struct gendisk *disk, fmode_t mode)
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* In autoclear mode, stop the loop thread
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* and remove configuration after last close.
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*/
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__loop_clr_fd(lo, true);
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loop_schedule_rundown(lo);
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return;
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} else if (lo->lo_state == Lo_bound) {
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/*
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@ -56,6 +56,7 @@ struct loop_device {
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struct gendisk *lo_disk;
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struct mutex lo_mutex;
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bool idr_visible;
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struct work_struct rundown_work;
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};
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struct loop_cmd {
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