Unverified Commit f298e376 authored by David Howells's avatar David Howells Committed by Christian Brauner
Browse files

netfs: Fix collection of results during pause when collection offloaded 



A netfs read request can run in one of two modes: for synchronous reads
writes, the app thread does the collection of results and for asynchronous
reads, this is offloaded to a worker thread.  This is controlled by the
NETFS_RREQ_OFFLOAD_COLLECTION flag.

Now, if a subrequest incurs an error, the NETFS_RREQ_PAUSE flag is set to
stop the issuing loop temporarily from issuing more subrequests until a
retry is successful or the request is abandoned.

When the issuing loop sees NETFS_RREQ_PAUSE, it jumps to
netfs_wait_for_pause() which will wait for the PAUSE flag to be cleared -
and whilst it is waiting, it will call out to the collector as more results
acrue...  But this is the wrong thing to do if OFFLOAD_COLLECTION is set as
we can then end up with both the app thread and the work item collecting
results simultaneously.

This manifests itself occasionally when running the generic/323 xfstest
against multichannel cifs as an oops that's a bit random but frequently
involving io_submit() (the test does lots of simultaneous async DIO reads).

Fix this by only doing the collection in netfs_wait_for_pause() if the
NETFS_RREQ_OFFLOAD_COLLECTION is not set.

Fixes: e2d46f2e ("netfs: Change the read result collector to only use one work item")
Reported-by: default avatarSteve French <stfrench@microsoft.com>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20250314164201.1993231-2-dhowells@redhat.com


Acked-by: default avatar"Paulo Alcantara (Red Hat)" <pc@manguebit.com>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent d9ecc771

fs/netfs/read_collect.c

+10 −8
Original line number Diff line number Diff line
@@ -682,6 +682,7 @@ void netfs_wait_for_pause(struct netfs_io_request *rreq) 
		trace_netfs_rreq(rreq, netfs_rreq_trace_wait_queue);

		prepare_to_wait(&rreq->waitq, &myself, TASK_UNINTERRUPTIBLE);



		if (!test_bit(NETFS_RREQ_OFFLOAD_COLLECTION, &rreq->flags)) {

			subreq = list_first_entry_or_null(&stream->subrequests,

							  struct netfs_io_subrequest, rreq_link);

			if (subreq &&
@@ -691,6 +692,7 @@ void netfs_wait_for_pause(struct netfs_io_request *rreq) 
				netfs_read_collection(rreq);

				continue;

			}

		}



		if (!test_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags) ||

		    !test_bit(NETFS_RREQ_PAUSE, &rreq->flags))