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Commit fcac03ab authored by Milan Broz's avatar Milan Broz Committed by Linus Torvalds
Browse files

dm snapshot: fix invalidation deadlock 



Process persistent exception store metadata IOs in a separate thread.

A snapshot may become invalid while inside generic_make_request().
A synchronous write is then needed to update the metadata while still
inside that function.  Since the introduction of
md-dm-reduce-stack-usage-with-stacked-block-devices.patch this has to
be performed by a separate thread to avoid deadlock.

Signed-off-by: default avatarMilan Broz <mbroz@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 596f138e

drivers/md/dm-exception-store.c

+43 −5
Original line number Original line Diff line number Diff line
@@ -125,6 +125,8 @@ struct pstore { 
	uint32_t callback_count;

	uint32_t callback_count;

	struct commit_callback *callbacks;

	struct commit_callback *callbacks;

	struct dm_io_client *io_client;

	struct dm_io_client *io_client;



	struct workqueue_struct *metadata_wq;

};

};





static unsigned sectors_to_pages(unsigned sectors)

static unsigned sectors_to_pages(unsigned sectors)
@@ -156,10 +158,24 @@ static void free_area(struct pstore *ps) 
	ps->area = NULL;

	ps->area = NULL;

}

}





struct mdata_req {

	struct io_region *where;

	struct dm_io_request *io_req;

	struct work_struct work;

	int result;

};



static void do_metadata(struct work_struct *work)

{

	struct mdata_req *req = container_of(work, struct mdata_req, work);



	req->result = dm_io(req->io_req, 1, req->where, NULL);

}



/*

/*

 * Read or write a chunk aligned and sized block of data from a device.

 * Read or write a chunk aligned and sized block of data from a device.

 */

 */

static int chunk_io(struct pstore *ps, uint32_t chunk, int rw)

static int chunk_io(struct pstore *ps, uint32_t chunk, int rw, int metadata)

{

{

	struct io_region where = {

	struct io_region where = {

		.bdev = ps->snap->cow->bdev,

		.bdev = ps->snap->cow->bdev,
@@ -173,8 +189,23 @@ static int chunk_io(struct pstore *ps, uint32_t chunk, int rw) 
		.client = ps->io_client,

		.client = ps->io_client,

		.notify.fn = NULL,

		.notify.fn = NULL,

	};

	};

	struct mdata_req req;





	if (!metadata)

		return dm_io(&io_req, 1, &where, NULL);

		return dm_io(&io_req, 1, &where, NULL);



	req.where = &where;

	req.io_req = &io_req;



	/*

	 * Issue the synchronous I/O from a different thread

	 * to avoid generic_make_request recursion.

	 */

	INIT_WORK(&req.work, do_metadata);

	queue_work(ps->metadata_wq, &req.work);

	flush_workqueue(ps->metadata_wq);



	return req.result;

}

}





/*

/*
@@ -189,7 +220,7 @@ static int area_io(struct pstore *ps, uint32_t area, int rw) 
	/* convert a metadata area index to a chunk index */

	/* convert a metadata area index to a chunk index */

	chunk = 1 + ((ps->exceptions_per_area + 1) * area);

	chunk = 1 + ((ps->exceptions_per_area + 1) * area);





	r = chunk_io(ps, chunk, rw);

	r = chunk_io(ps, chunk, rw, 0);

	if (r)

	if (r)

		return r;

		return r;
@@ -230,7 +261,7 @@ static int read_header(struct pstore *ps, int *new_snapshot) 
	if (r)

	if (r)

		return r;

		return r;





	r = chunk_io(ps, 0, READ);

	r = chunk_io(ps, 0, READ, 1);

	if (r)

	if (r)

		goto bad;

		goto bad;
@@ -292,7 +323,7 @@ static int write_header(struct pstore *ps) 
	dh->version = cpu_to_le32(ps->version);

	dh->version = cpu_to_le32(ps->version);

	dh->chunk_size = cpu_to_le32(ps->snap->chunk_size);

	dh->chunk_size = cpu_to_le32(ps->snap->chunk_size);





	return chunk_io(ps, 0, WRITE);

	return chunk_io(ps, 0, WRITE, 1);

}

}





/*

/*
@@ -409,6 +440,7 @@ static void persistent_destroy(struct exception_store *store) 
{

{

	struct pstore *ps = get_info(store);

	struct pstore *ps = get_info(store);





	destroy_workqueue(ps->metadata_wq);

	dm_io_client_destroy(ps->io_client);

	dm_io_client_destroy(ps->io_client);

	vfree(ps->callbacks);

	vfree(ps->callbacks);

	free_area(ps);

	free_area(ps);
@@ -588,6 +620,12 @@ int dm_create_persistent(struct exception_store *store) 
	atomic_set(&ps->pending_count, 0);

	atomic_set(&ps->pending_count, 0);

	ps->callbacks = NULL;

	ps->callbacks = NULL;





	ps->metadata_wq = create_singlethread_workqueue("ksnaphd");

	if (!ps->metadata_wq) {

		DMERR("couldn't start header metadata update thread");

		return -ENOMEM;

	}



	store->destroy = persistent_destroy;

	store->destroy = persistent_destroy;

	store->read_metadata = persistent_read_metadata;

	store->read_metadata = persistent_read_metadata;

	store->prepare_exception = persistent_prepare;

	store->prepare_exception = persistent_prepare;