Commit b6f8fec4 authored Mar 08, 2017 by Jan Kara Committed by Jens Axboe Mar 08, 2017

block: Allow bdi re-registration



SCSI can call device_add_disk() several times for one request queue when
a device in unbound and bound, creating new gendisk each time. This will
lead to bdi being repeatedly registered and unregistered. This was not a
big problem until commit 165a5e22 "block: Move bdi_unregister() to
del_gendisk()" since bdi was only registered repeatedly (bdi_register()
handles repeated calls fine, only we ended up leaking reference to
gendisk due to overwriting bdi->owner) but unregistered only in
blk_cleanup_queue() which didn't get called repeatedly. After
165a5e22 we were doing correct bdi_register() - bdi_unregister()
cycles however bdi_unregister() is not prepared for it. So make sure
bdi_unregister() cleans up bdi in such a way that it is prepared for
a possible following bdi_register() call.

An easy way to provoke this behavior is to enable
CONFIG_DEBUG_TEST_DRIVER_REMOVE and use scsi_debug driver to create a
scsi disk which immediately hangs without this fix.

Fixes: 165a5e22
Signed-off-by: Jan Kara <jack@suse.cz>
Tested-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

parent b0bfdfc2

mm/backing-dev.c

+7 −0

Original line number	Original line	Diff line number	Diff line
	@@ -710,6 +710,11 @@ static void cgwb_bdi_destroy(struct backing_dev_info *bdi)
	*/		*/
	atomic_dec(&bdi->usage_cnt);		atomic_dec(&bdi->usage_cnt);
	wait_event(cgwb_release_wait, !atomic_read(&bdi->usage_cnt));		wait_event(cgwb_release_wait, !atomic_read(&bdi->usage_cnt));
			/*
			* Grab back our reference so that we hold it when @bdi gets
			* re-registered.
			*/
			atomic_inc(&bdi->usage_cnt);
	}		}

	/**		/**
	@@ -857,6 +862,8 @@ int bdi_register_owner(struct backing_dev_info bdi, struct device owner)
	MINOR(owner->devt));		MINOR(owner->devt));
	if (rc)		if (rc)
	return rc;		return rc;
			/* Leaking owner reference... */
			WARN_ON(bdi->owner);
	bdi->owner = owner;		bdi->owner = owner;
	get_device(owner);		get_device(owner);
	return 0;		return 0;

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