netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 22 insertions, 0 deletions

diff --git a/drivers/accessibility/speakup/TODO b/drivers/accessibility/speakup/TODO
new file mode 100644
index 000000000..d4ca093bf
--- /dev/null
+++ b/drivers/accessibility/speakup/TODO
@@ -0,0 +1,22 @@
+Speakup project home:  http://www.linux-speakup.org
+
+Mailing List:  speakup@linux-speakup.org
+
+Speakup is a kernel based screen review package for the linux operating
+system.  It allows blind users to interact with applications on the
+linux console by means of synthetic speech.
+
+Currently, speakup has one issue we know of.
+
+It seems to only happen on SMP systems. It seems that text in the output buffer
+gets garbled because a lock is not set. This bug happens regularly, but no one
+has been able to find a situation which produces it consistently.
+
+Patches, suggestions, corrections, etc, are definitely welcome.
+
+We prefer that you contact us on the mailing list; however, if you do
+not want to subscribe to a mailing list, send your email to all of the
+following:
+
+okash.khawaja@gmail.com, w.d.hubbs@gmail.com, chris@the-brannons.com,
+kirk@reisers.ca and samuel.thibault@ens-lyon.org.