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Commit c05f3e3c authored by Roger Pau Monne's avatar Roger Pau Monne Committed by Konrad Rzeszutek Wilk
Browse files

xen-blkback: fix shutdown race 



Introduce a new variable to keep track of the number of in-flight
requests. We need to make sure that when xen_blkif_put is called the
request has already been freed and we can safely free xen_blkif, which
was not the case before.

Signed-off-by: default avatarRoger Pau Monné <roger.pau@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Tested-by: default avatarMatt Rushton <mrushton@amazon.com>
Reviewed-by: default avatarMatt Rushton <mrushton@amazon.com>
Cc: Matt Wilson <msw@amazon.com>
Cc: Ian Campbell <Ian.Campbell@citrix.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent ef753411

drivers/block/xen-blkback/blkback.c

+22 −10
Original line number Diff line number Diff line
@@ -943,9 +943,7 @@ static void xen_blk_drain_io(struct xen_blkif *blkif) 
{

	atomic_set(&blkif->drain, 1);

	do {

		/* The initial value is one, and one refcnt taken at the

		 * start of the xen_blkif_schedule thread. */

		if (atomic_read(&blkif->refcnt) <= 2)

		if (atomic_read(&blkif->inflight) == 0)

			break;

		wait_for_completion_interruptible_timeout(

				&blkif->drain_complete, HZ);
@@ -985,17 +983,30 @@ static void __end_block_io_op(struct pending_req *pending_req, int error) 
	 * the proper response on the ring.

	 */

	if (atomic_dec_and_test(&pending_req->pendcnt)) {

		xen_blkbk_unmap(pending_req->blkif,

		struct xen_blkif *blkif = pending_req->blkif;



		xen_blkbk_unmap(blkif,

		                pending_req->segments,

		                pending_req->nr_pages);

		make_response(pending_req->blkif, pending_req->id,

		make_response(blkif, pending_req->id,

			      pending_req->operation, pending_req->status);

		xen_blkif_put(pending_req->blkif);

		if (atomic_read(&pending_req->blkif->refcnt) <= 2) {

			if (atomic_read(&pending_req->blkif->drain))

				complete(&pending_req->blkif->drain_complete);

		free_req(blkif, pending_req);

		/*

		 * Make sure the request is freed before releasing blkif,

		 * or there could be a race between free_req and the

		 * cleanup done in xen_blkif_free during shutdown.

		 *

		 * NB: The fact that we might try to wake up pending_free_wq

		 * before drain_complete (in case there's a drain going on)

		 * it's not a problem with our current implementation

		 * because we can assure there's no thread waiting on

		 * pending_free_wq if there's a drain going on, but it has

		 * to be taken into account if the current model is changed.

		 */

		if (atomic_dec_and_test(&blkif->inflight) && atomic_read(&blkif->drain)) {

			complete(&blkif->drain_complete);

		}

		free_req(pending_req->blkif, pending_req);

		xen_blkif_put(blkif);

	}

}
@@ -1249,6 +1260,7 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif, 
	 * below (in "!bio") if we are handling a BLKIF_OP_DISCARD.

	 */

	xen_blkif_get(blkif);

	atomic_inc(&blkif->inflight);



	for (i = 0; i < nseg; i++) {

		while ((bio == NULL) ||

drivers/block/xen-blkback/common.h

+1 −0
Original line number Diff line number Diff line
@@ -278,6 +278,7 @@ struct xen_blkif { 
	/* for barrier (drain) requests */

	struct completion	drain_complete;

	atomic_t		drain;

	atomic_t		inflight;

	/* One thread per one blkif. */

	struct task_struct	*xenblkd;

	unsigned int		waiting_reqs;

drivers/block/xen-blkback/xenbus.c

+1 −0
Original line number Diff line number Diff line
@@ -128,6 +128,7 @@ static struct xen_blkif *xen_blkif_alloc(domid_t domid) 
	INIT_LIST_HEAD(&blkif->persistent_purge_list);

	blkif->free_pages_num = 0;

	atomic_set(&blkif->persistent_gnt_in_use, 0);

	atomic_set(&blkif->inflight, 0);



	INIT_LIST_HEAD(&blkif->pending_free);