USB: cdc-acm: fix write and suspend race
commit 5a345c20c17d87099224a4be12e69e5bd7023dca upstream.
Fix race between write() and suspend() which could lead to writes being
dropped (or I/O while suspended) if the device is runtime suspended
while a write request is being processed.
Specifically, suspend() releases the write_lock after determining the
device is idle but before incrementing the susp_count, thus leaving a
window where a concurrent write() can submit an urb.
Fixes: 11ea859d64b6 ("USB: additional power savings for cdc-acm devices
that support remote wakeup")
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 89cce1a..a456d88 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1434,18 +1434,15 @@
struct acm *acm = usb_get_intfdata(intf);
int cnt;
- if (PMSG_IS_AUTO(message)) {
- int b;
-
- spin_lock_irq(&acm->write_lock);
- b = acm->transmitting;
- spin_unlock_irq(&acm->write_lock);
- if (b)
- return -EBUSY;
- }
-
spin_lock_irq(&acm->read_lock);
spin_lock(&acm->write_lock);
+ if (PMSG_IS_AUTO(message)) {
+ if (acm->transmitting) {
+ spin_unlock(&acm->write_lock);
+ spin_unlock_irq(&acm->read_lock);
+ return -EBUSY;
+ }
+ }
cnt = acm->susp_count++;
spin_unlock(&acm->write_lock);
spin_unlock_irq(&acm->read_lock);