linux-kernel - [PATCH 5.4 19/54] cifs: allow syscalls to be restarted in __smb_send

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Date:   Thu, 10 Dec 2020 15:26:56 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Paulo Alcantara (SUSE)" <pc@....nz>,
        Ronnie Sahlberg <lsahlber@...hat.com>,
        Pavel Shilovsky <pshilov@...rosoft.com>,
        Steve French <stfrench@...rosoft.com>
Subject: [PATCH 5.4 19/54] cifs: allow syscalls to be restarted in __smb_send_rqst()

From: Paulo Alcantara <pc@....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@....nz>
CC: Stable <stable@...r.kernel.org>
Reviewed-by: Ronnie Sahlberg <lsahlber@...hat.com>
Reviewed-by: Pavel Shilovsky <pshilov@...rosoft.com>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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 */