Am testing this fix now (especially with multichannel scenarios which
were failing before)
On Fri, Feb 28, 2025 at 11:22 AM David Howells <dhowells@xxxxxxxxxx> wrote:
>
>
> 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: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
> Reported-by: Steve French <stfrench@xxxxxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> cc: Paulo Alcantara <pc@xxxxxxxxxxxxx>
> cc: Jeff Layton <jlayton@xxxxxxxxxx>
> cc: linux-cifs@xxxxxxxxxxxxxxx
> cc: netfs@xxxxxxxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> ---
> fs/netfs/read_collect.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/fs/netfs/read_collect.c b/fs/netfs/read_collect.c
> index 636cc5a98ef5..23c75755ad4e 100644
> --- a/fs/netfs/read_collect.c
> +++ b/fs/netfs/read_collect.c
> @@ -682,14 +682,16 @@ 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);
>
> - subreq = list_first_entry_or_null(&stream->subrequests,
> - struct netfs_io_subrequest, rreq_link);
> - if (subreq &&
> - (!test_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags) ||
> - test_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags))) {
> - __set_current_state(TASK_RUNNING);
> - netfs_read_collection(rreq);
> - continue;
> + 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 &&
> + (!test_bit(NETFS_SREQ_IN_PROGRESS, &subreq->flags) ||
> + test_bit(NETFS_SREQ_MADE_PROGRESS, &subreq->flags))) {
> + __set_current_state(TASK_RUNNING);
> + netfs_read_collection(rreq);
> + continue;
> + }
> }
>
> if (!test_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags) ||
>
>
--
Thanks,
Steve
