smb: client: transport: avoid reconnects triggered by pending task work

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>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/client/transport.c b/fs/smb/client/transport.c
index a61ba7f3fb86bd0925180918993a22016069bc7d..940e901071343d0aba219d11571b94ef648fe5fa 100644 (file)
--- 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))) {