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authorRoger Pau Monne <roger.pau@citrix.com>2014-02-04 11:26:14 +0100
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2014-02-07 12:59:30 -0500
commitc05f3e3c85df1d89673e00cee7ece5ae4eb4c6ec (patch)
treebf77875d2640a0f4388aa9c20d7867e51878c45a
parentef753411339eae46b9a3151906901f8bfd12b0f1 (diff)
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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: Roger Pau Monné <roger.pau@citrix.com> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: David Vrabel <david.vrabel@citrix.com> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> Tested-by: Matt Rushton <mrushton@amazon.com> Reviewed-by: Matt Rushton <mrushton@amazon.com> Cc: Matt Wilson <msw@amazon.com> Cc: Ian Campbell <Ian.Campbell@citrix.com> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
-rw-r--r--drivers/block/xen-blkback/blkback.c32
-rw-r--r--drivers/block/xen-blkback/common.h1
-rw-r--r--drivers/block/xen-blkback/xenbus.c1
3 files changed, 24 insertions, 10 deletions
diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index dcfe49fd3cb4..394fa2eabf87 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -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) ||
diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index f733d7627120..e40326a7f707 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -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;
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 8afef67fecdd..84973c6a856a 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -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);