From 6f6485463aada1ec6a0f3db6a03eb8e393d6bb55 Mon Sep 17 00:00:00 2001
From: Johan Hovold <jhovold@gmail.com>
Date: Sat, 9 Nov 2013 12:38:09 +0100
Subject: [PATCH] USB: serial: fix race in generic write
Fix race in generic write implementation, which could lead to
temporarily degraded throughput.
The current generic write implementation introduced by commit
27c7acf22047 ("USB: serial: reimplement generic fifo-based writes") has
always had this bug, although it's fairly hard to trigger and the
consequences are not likely to be noticed.
Specifically, a write() on one CPU while the completion handler is
running on another could result in only one of the two write urbs being
utilised to empty the remainder of the write fifo (unless there is a
second write() that doesn't race during that time).
Cc: stable <stable@vger.kernel.org> # 2.6.35
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/usb/serial/generic.c | 10 +---------
1 file changed, 1 insertion(+), 9 deletions(-)
diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index 2b01ec8651c29..e36b25a2fa02b 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -173,16 +173,8 @@ int usb_serial_generic_write_start(struct usb_serial_port *port,
clear_bit_unlock(USB_SERIAL_WRITE_BUSY, &port->flags);
return result;
}
- /*
- * Try sending off another urb, unless called from completion handler
- * (in which case there will be no free urb or no data).
- */
- if (mem_flags != GFP_ATOMIC)
- goto retry;
- clear_bit_unlock(USB_SERIAL_WRITE_BUSY, &port->flags);
-
- return 0;
+ goto retry; /* try sending off another urb */
}
EXPORT_SYMBOL_GPL(usb_serial_generic_write_start);