netfs: Fix the handling of stream->front by removing it

[ Upstream commit 0e764b9d46071668969410ec5429be0e2f38c6d3 ]

The netfs_io_stream::front member is meant to point to the subrequest
currently being collected on a stream, but it isn't actually used this way
by direct write (which mostly ignores it).  However, there's a tracepoint
which looks at it.  Further, stream->front is actually redundant with
stream->subrequests.next.

Fix the potential problem in the direct code by just removing the member
and using stream->subrequests.next instead, thereby also simplifying the
code.

Fixes: a0b4c7a49137 ("netfs: Fix unbuffered/DIO writes to dispatch subrequests in strict sequence")
Reported-by: Paulo Alcantara <pc@manguebit.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/4158599.1774426817@warthog.procyon.org.uk
Reviewed-by: Paulo Alcantara (Red Hat) <pc@manguebit.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

7 files changed, 7 insertions, 12 deletions

diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
index 37ab6f28b5ad..88361e8c7096 100644
--- a/fs/netfs/buffered_read.c
+++ b/fs/netfs/buffered_read.c
@@ -171,9 +171,8 @@ static void netfs_queue_read(struct netfs_io_request *rreq,
 	spin_lock(&rreq->lock);
 	list_add_tail(&subreq->rreq_link, &stream->subrequests);
 	if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
-		stream->front = subreq;
 		if (!stream->active) {
-			stream->collected_to = stream->front->start;
+			stream->collected_to = subreq->start;
 			/* Store list pointers before active flag */
 			smp_store_release(&stream->active, true);
 		}
diff --git a/fs/netfs/direct_read.c b/fs/netfs/direct_read.c
index a498ee8d6674..f72e6da88cca 100644
--- a/fs/netfs/direct_read.c
+++ b/fs/netfs/direct_read.c
@@ -71,9 +71,8 @@ static int netfs_dispatch_unbuffered_reads(struct netfs_io_request *rreq)
 		spin_lock(&rreq->lock);
 		list_add_tail(&subreq->rreq_link, &stream->subrequests);
 		if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
-			stream->front = subreq;
 			if (!stream->active) {
-				stream->collected_to = stream->front->start;
+				stream->collected_to = subreq->start;
 				/* Store list pointers before active flag */
 				smp_store_release(&stream->active, true);
 			}
diff --git a/fs/netfs/direct_write.c b/fs/netfs/direct_write.c
index 4d9760e36c11..f9ab69de3e29 100644
--- a/fs/netfs/direct_write.c
+++ b/fs/netfs/direct_write.c
@@ -111,7 +111,6 @@ static int netfs_unbuffered_write(struct netfs_io_request *wreq)
 			netfs_prepare_write(wreq, stream, wreq->start + wreq->transferred);
 			subreq = stream->construct;
 			stream->construct = NULL;
-			stream->front = NULL;
 		}
 
 		/* Check if (re-)preparation failed. */
diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
index 137f0e28a44c..e5f6665b3341 100644
--- a/fs/netfs/read_collect.c
+++ b/fs/netfs/read_collect.c
@@ -205,7 +205,8 @@ reassess:
 	 * in progress.  The issuer thread may be adding stuff to the tail
 	 * whilst we're doing this.
 	 */
-	front = READ_ONCE(stream->front);
+	front = list_first_entry_or_null(&stream->subrequests,
+					 struct netfs_io_subrequest, rreq_link);
 	while (front) {
 		size_t transferred;
 
@@ -301,7 +302,6 @@ reassess:
 		list_del_init(&front->rreq_link);
 		front = list_first_entry_or_null(&stream->subrequests,
 						 struct netfs_io_subrequest, rreq_link);
-		stream->front = front;
 		spin_unlock(&rreq->lock);
 		netfs_put_subrequest(remove,
 				     notes & ABANDON_SREQ ?
diff --git a/fs/netfs/read_single.c b/fs/netfs/read_single.c
index 8e6264f62a8f..d0e23bc42445 100644
--- a/fs/netfs/read_single.c
+++ b/fs/netfs/read_single.c
@@ -107,7 +107,6 @@ static int netfs_single_dispatch_read(struct netfs_io_request *rreq)
 	spin_lock(&rreq->lock);
 	list_add_tail(&subreq->rreq_link, &stream->subrequests);
 	trace_netfs_sreq(subreq, netfs_sreq_trace_added);
-	stream->front = subreq;
 	/* Store list pointers before active flag */
 	smp_store_release(&stream->active, true);
 	spin_unlock(&rreq->lock);
diff --git a/fs/netfs/write_collect.c b/fs/netfs/write_collect.c
index 83eb3dc1adf8..b194447f4b11 100644
--- a/fs/netfs/write_collect.c
+++ b/fs/netfs/write_collect.c
@@ -228,7 +228,8 @@ reassess_streams:
 		if (!smp_load_acquire(&stream->active))
 			continue;
 
-		front = stream->front;
+		front = list_first_entry_or_null(&stream->subrequests,
+						 struct netfs_io_subrequest, rreq_link);
 		while (front) {
 			trace_netfs_collect_sreq(wreq, front);
 			//_debug("sreq [%x] %llx %zx/%zx",
@@ -279,7 +280,6 @@ reassess_streams:
 			list_del_init(&front->rreq_link);
 			front = list_first_entry_or_null(&stream->subrequests,
 							 struct netfs_io_subrequest, rreq_link);
-			stream->front = front;
 			spin_unlock(&wreq->lock);
 			netfs_put_subrequest(remove,
 					     notes & SAW_FAILURE ?
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c
index 437268f65640..2db688f94125 100644
--- a/fs/netfs/write_issue.c
+++ b/fs/netfs/write_issue.c
@@ -206,9 +206,8 @@ void netfs_prepare_write(struct netfs_io_request *wreq,
 	spin_lock(&wreq->lock);
 	list_add_tail(&subreq->rreq_link, &stream->subrequests);
 	if (list_is_first(&subreq->rreq_link, &stream->subrequests)) {
-		stream->front = subreq;
 		if (!stream->active) {
-			stream->collected_to = stream->front->start;
+			stream->collected_to = subreq->start;
 			/* Write list pointers before active flag */
 			smp_store_release(&stream->active, true);
 		}