linux-kernel - [PATCH] cifs: Fix cifs readv callback merge resolution issue

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Message-ID: <1947793.1726494616@warthog.procyon.org.uk>
Date: Mon, 16 Sep 2024 14:50:16 +0100
From: David Howells <dhowells@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: dhowells@...hat.com, Christian Brauner <brauner@...nel.org>,
    linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
    Steve French <stfrench@...rosoft.com>
Subject: [PATCH] cifs: Fix cifs readv callback merge resolution issue

Fix an upstream merge resolution issue[1].  Prior to the netfs read
healpers, the SMB1 asynchronous read callback, cifs_readv_worker()
performed the cleanup for the operation in the network message processing
loop, potentially slowing down the processing of incoming SMB messages.

With commit a68c74865f51 ("cifs: Fix SMB1 readv/writev callback in the same
way as SMB2/3"), this was moved to a worker thread (as is done in the
SMB2/3 transport variant).  However, the "was_async" argument to
netfs_subreq_terminated (which was originally incorrectly "false" got
flipped to "true" - which was then incorrect because, being in a kernel
thread, it's not in an async context).

This got corrected in the sample merge[2], but Linus, not unreasonably,
switched it back to its previous value.

Note that this value tells netfslib whether or not it can run sleepable
stuff or stuff that takes a long time, such as retries and cleanups, in the
calling thread, or whether it should offload to a worker thread.

Fix this so that it is "false".  The callback to netfslib in both SMB1 and
SMB2/3 now gets offloaded from the network message thread to a separate
worker thread and thus it's fine to do the slow work in this thread.

Fixes: 35219bc5c71f ("Merge tag 'vfs-6.12.netfs' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs")
Signed-off-by: David Howells <dhowells@...hat.com>
cc: Linus Torvalds <torvalds@...ux-foundation.org>
cc: Steve French <stfrench@...rosoft.com>
cc: Paulo Alcantara <pc@...guebit.com>
cc: Christian Brauner <brauner@...nel.org>
cc: Jeff Layton <jlayton@...nel.org>
cc: linux-cifs@...r.kernel.org
cc: netfs@...ts.linux.dev
cc: linux-fsdevel@...r.kernel.org
Link: https://lore.kernel.org/r/CAHk-=wjr8fxk20-wx=63mZruW1LTvBvAKya1GQ1EhyzXb-okMA@mail.gmail.com/ [1]
Link: https://lore.kernel.org/linux-fsdevel/20240913-vfs-netfs-39ef6f974061@brauner/ [2]
---
 fs/smb/client/cifssmb.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/smb/client/cifssmb.c b/fs/smb/client/cifssmb.c
index d81da161d3ed..7f3b37120a21 100644
--- a/fs/smb/client/cifssmb.c
+++ b/fs/smb/client/cifssmb.c
@@ -1266,7 +1266,7 @@ static void cifs_readv_worker(struct work_struct *work)
 	struct cifs_io_subrequest *rdata =
 		container_of(work, struct cifs_io_subrequest, subreq.work);

-	netfs_read_subreq_terminated(&rdata->subreq, rdata->result, true);
+	netfs_read_subreq_terminated(&rdata->subreq, rdata->result, false);
 }

 static void