[PATCH 1/2] smb: client: transport: avoid reconnects triggered by pending task work

[Fiona Ebner <f.ebner@proxmox.com>]

When io_uring is used in the same task as CIFS, there might be
unnecessary reconnects, causing issues in user-space applications
like QEMU with a log like:

> CIFS: VFS: \\10.10.100.81 Error -512 sending data on socket to server

Certain io_uring completions might be added to task_work with
notify_method being TWA_SIGNAL and thus TIF_NOTIFY_SIGNAL is set for
the task.

In __smb_send_rqst(), signals are masked before calling
smb_send_kvec(), but the masking does not apply to TIF_NOTIFY_SIGNAL.

If sk_stream_wait_memory() is reached via sock_sendmsg() while
TIF_NOTIFY_SIGNAL is set, signal_pending(current) will evaluate to
true there, and -EINTR will be propagated all the way from
sk_stream_wait_memory() to sock_sendmsg() in smb_send_kvec().
Afterwards, __smb_send_rqst() will see that not everything was written
and reconnect.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 fs/smb/client/transport.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/transport.c b/fs/smb/client/transport.c
index a61ba7f3fb86..940e90107134 100644
--- a/fs/smb/client/transport.c
+++ b/fs/smb/client/transport.c
@@ -22,6 +22,7 @@
 #include <linux/mempool.h>
 #include <linux/sched/signal.h>
 #include <linux/task_io_accounting_ops.h>
+#include <linux/task_work.h>
 #include "cifspdu.h"
 #include "cifsglob.h"
 #include "cifsproto.h"
@@ -173,9 +174,16 @@ smb_send_kvec(struct TCP_Server_Info *server, struct msghdr *smb_msg,
 		 * send a packet.  In most cases if we fail to send
 		 * after the retries we will kill the socket and
 		 * reconnect which may clear the network problem.
+		 *
+		 * Even if regular signals are masked, EINTR might be
+		 * propagated from sk_stream_wait_memory() to here when
+		 * TIF_NOTIFY_SIGNAL is used for task work. For example,
+		 * certain io_uring completions will use that. Treat
+		 * having EINTR with pending task work the same as EAGAIN
+		 * to avoid unnecessary reconnects.
 		 */
 		rc = sock_sendmsg(ssocket, smb_msg);
-		if (rc == -EAGAIN) {
+		if (rc == -EAGAIN || unlikely(rc == -EINTR && task_work_pending(current))) {
 			retries++;
 			if (retries >= 14 ||
 			    (!server->noblocksnd && (retries > 2))) {
-- 
2.47.2