From 6f6485463aada1ec6a0f3db6a03eb8e393d6bb55 Mon Sep 17 00:00:00 2001 From: Johan Hovold Date: Sat, 9 Nov 2013 12:38:09 +0100 Subject: 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 # 2.6.35 Signed-off-by: Johan Hovold Signed-off-by: Greg Kroah-Hartman --- drivers/usb/serial/generic.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-) (limited to 'drivers/usb/serial/generic.c') diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c index 2b01ec8651c..e36b25a2fa0 100644 --- a/drivers/usb/serial/generic.c +++ b/drivers/usb/serial/generic.c @@ -173,16 +173,8 @@ retry: 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); -- cgit v1.2.3-70-g09d2 From 043e3f834530e15e89c58c1b7af59cc646700134 Mon Sep 17 00:00:00 2001 From: Johan Hovold Date: Sat, 9 Nov 2013 12:38:10 +0100 Subject: USB: serial: fix write memory-allocation flag Fix regression introduced by commit 818f60365a29 ("USB: serial: add memory flags to usb_serial_generic_write_start"), which incorrectly used GFP_KERNEL in write(), which must not not sleep. Reported-by: Dave Jones Tested-by: Dave Jones Cc: Dave Jones Signed-off-by: Johan Hovold Signed-off-by: Greg Kroah-Hartman --- drivers/usb/serial/generic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'drivers/usb/serial/generic.c') diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c index e36b25a2fa0..b63ce023f96 100644 --- a/drivers/usb/serial/generic.c +++ b/drivers/usb/serial/generic.c @@ -200,7 +200,7 @@ int usb_serial_generic_write(struct tty_struct *tty, return 0; count = kfifo_in_locked(&port->write_fifo, buf, count, &port->lock); - result = usb_serial_generic_write_start(port, GFP_KERNEL); + result = usb_serial_generic_write_start(port, GFP_ATOMIC); if (result) return result; -- cgit v1.2.3-70-g09d2