[PATCH 5.4 19/54] cifs: allow syscalls to be restarted in __smb_send_rqst()

Greg Kroah-Hartman
2020-12-10T14:43:36Z

From: Paulo Alcantara <pc@cjr.nz>

commit 6988a619f5b79e4efadea6e19dcfe75fbcd350b5 upstream.

A customer has reported that several files in their multi-threaded app
were left with size of 0 because most of the read(2) calls returned
-EINTR and they assumed no bytes were read. Obviously, they could
have fixed it by simply retrying on -EINTR.

We noticed that most of the -EINTR on read(2) were due to real-time
signals sent by glibc to process wide credential changes (SIGRT_1),
and its signal handler had been established with SA_RESTART, in which
case those calls could have been automatically restarted by the
kernel.

Let the kernel decide to whether or not restart the syscalls when
there is a signal pending in __smb_send_rqst() by returning
-ERESTARTSYS. If it can't, it will return -EINTR anyway.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
CC: Stable <stable@vger.kernel.org>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/cifs/transport.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -340,8 +340,8 @@ __smb_send_rqst(struct TCP_Server_Info *
return -EAGAIN;

if (signal_pending(current)) {
- cifs_dbg(FYI, "signal is pending before sending any data\n");
- return -EINTR;
+ cifs_dbg(FYI, "signal pending before send request\n");
+ return -ERESTARTSYS;
}

/* cork the socket */