linux-kernel - [PATCH 01/11] netfs: Fix hang due to missing case in final DIO read result collection

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Message-ID: <20250623124835.1106414-2-dhowells@redhat.com>
Date: Mon, 23 Jun 2025 13:48:21 +0100
From: David Howells <dhowells@...hat.com>
To: Christian Brauner <christian@...uner.io>,
	Steve French <sfrench@...ba.org>
Cc: David Howells <dhowells@...hat.com>,
	Paulo Alcantara <pc@...guebit.com>,
	netfs@...ts.linux.dev,
	linux-afs@...ts.infradead.org,
	linux-cifs@...r.kernel.org,
	linux-nfs@...r.kernel.org,
	ceph-devel@...r.kernel.org,
	v9fs@...ts.linux.dev,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Paulo Alcantara <pc@...guebit.org>
Subject: [PATCH 01/11] netfs: Fix hang due to missing case in final DIO read result collection

When doing a DIO read, if the subrequests we issue fail and cause the
request PAUSE flag to be set to put a pause on subrequest generation, we
may complete collection of the subrequests (possibly discarding them) prior
to the ALL_QUEUED flags being set.

In such a case, netfs_read_collection() doesn't see ALL_QUEUED being set
after netfs_collect_read_results() returns and will just return to the app
(the collector can be seen unpausing the generator in the trace log).

The subrequest generator can then set ALL_QUEUED and the app thread reaches
netfs_wait_for_request().  This causes netfs_collect_in_app() to be called
to see if we're done yet, but there's missing case here.

netfs_collect_in_app() will see that a thread is active and set inactive to
false, but won't see any subrequests in the read stream, and so won't set
need_collect to true.  The function will then just return 0, indicating
that the caller should just sleep until further activity (which won't be
forthcoming) occurs.

Fix this by making netfs_collect_in_app() check to see if an active thread
is complete - i.e. that ALL_QUEUED is set and the subrequests list is empty
- and to skip the sleep return path.  The collector will then be called
which will clear the request IN_PROGRESS flag, allowing the app to
progress.

Fixes: 2b1424cd131c ("netfs: Fix wait/wake to be consistent about the waitqueue used")
Reported-by: Steve French <sfrench@...ba.org>
Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: Paulo Alcantara <pc@...guebit.org>
cc: linux-cifs@...r.kernel.org
cc: netfs@...ts.linux.dev
cc: linux-fsdevel@...r.kernel.org
---
 fs/netfs/misc.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/netfs/misc.c b/fs/netfs/misc.c
index 43b67a28a8fa..0a54b1203486 100644
--- a/fs/netfs/misc.c
+++ b/fs/netfs/misc.c
@@ -381,7 +381,7 @@ void netfs_wait_for_in_progress_stream(struct netfs_io_request *rreq,
 static int netfs_collect_in_app(struct netfs_io_request *rreq,
 				bool (*collector)(struct netfs_io_request *rreq))
 {
-	bool need_collect = false, inactive = true;
+	bool need_collect = false, inactive = true, done = true;

 	for (int i = 0; i < NR_IO_STREAMS; i++) {
 		struct netfs_io_subrequest *subreq;
@@ -400,9 +400,11 @@ static int netfs_collect_in_app(struct netfs_io_request *rreq,
 			need_collect = true;
 			break;
 		}
+		if (subreq || !test_bit(NETFS_RREQ_ALL_QUEUED, &rreq->flags))
+			done = false;
 	}

-	if (!need_collect && !inactive)
+	if (!need_collect && !inactive && !done)
 		return 0; /* Sleep */

 	__set_current_state(TASK_RUNNING);