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Subject[32/65] USB: cdc-wdm: use two mutexes to allow simultaneous read and write
3.0-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Bjørn Mork <bjorn@mork.no>

commit e8537bd2c4f325a4796da33564ddcef9489b7feb upstream.

using a separate read and write mutex for locking is sufficient to make the
driver accept simultaneous read and write. This improves useability a lot.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/class/cdc-wdm.c | 49 +++++++++++++++++++++++++++-----------------
1 file changed, 31 insertions(+), 18 deletions(-)
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -88,7 +88,8 @@ struct wdm_device {
int count;
dma_addr_t shandle;
dma_addr_t ihandle;
- struct mutex lock;
+ struct mutex wlock;
+ struct mutex rlock;
wait_queue_head_t wait;
struct work_struct rxwork;
int werr;
@@ -323,7 +324,7 @@ static ssize_t wdm_write
}

/* concurrent writes and disconnect */
- r = mutex_lock_interruptible(&desc->lock);
+ r = mutex_lock_interruptible(&desc->wlock);
rv = -ERESTARTSYS;
if (r) {
kfree(buf);
@@ -386,7 +387,7 @@ static ssize_t wdm_write
out:
usb_autopm_put_interface(desc->intf);
outnp:
- mutex_unlock(&desc->lock);
+ mutex_unlock(&desc->wlock);
outnl:
return rv < 0 ? rv : count;
}
@@ -399,7 +400,7 @@ static ssize_t wdm_read
struct wdm_device *desc = file->private_data;


- rv = mutex_lock_interruptible(&desc->lock); /*concurrent reads */
+ rv = mutex_lock_interruptible(&desc->rlock); /*concurrent reads */
if (rv < 0)
return -ERESTARTSYS;

@@ -476,7 +477,7 @@ retry:
rv = cntr;

err:
- mutex_unlock(&desc->lock);
+ mutex_unlock(&desc->rlock);
return rv;
}

@@ -542,7 +543,8 @@ static int wdm_open(struct inode *inode,
}
intf->needs_remote_wakeup = 1;

- mutex_lock(&desc->lock);
+ /* using write lock to protect desc->count */
+ mutex_lock(&desc->wlock);
if (!desc->count++) {
desc->werr = 0;
desc->rerr = 0;
@@ -555,7 +557,7 @@ static int wdm_open(struct inode *inode,
} else {
rv = 0;
}
- mutex_unlock(&desc->lock);
+ mutex_unlock(&desc->wlock);
usb_autopm_put_interface(desc->intf);
out:
mutex_unlock(&wdm_mutex);
@@ -567,9 +569,11 @@ static int wdm_release(struct inode *ino
struct wdm_device *desc = file->private_data;

mutex_lock(&wdm_mutex);
- mutex_lock(&desc->lock);
+
+ /* using write lock to protect desc->count */
+ mutex_lock(&desc->wlock);
desc->count--;
- mutex_unlock(&desc->lock);
+ mutex_unlock(&desc->wlock);

if (!desc->count) {
dev_dbg(&desc->intf->dev, "wdm_release: cleanup");
@@ -667,7 +671,8 @@ next_desc:
desc = kzalloc(sizeof(struct wdm_device), GFP_KERNEL);
if (!desc)
goto out;
- mutex_init(&desc->lock);
+ mutex_init(&desc->rlock);
+ mutex_init(&desc->wlock);
spin_lock_init(&desc->iuspin);
init_waitqueue_head(&desc->wait);
desc->wMaxCommand = maxcom;
@@ -781,10 +786,12 @@ static void wdm_disconnect(struct usb_in
/* to terminate pending flushes */
clear_bit(WDM_IN_USE, &desc->flags);
spin_unlock_irqrestore(&desc->iuspin, flags);
- mutex_lock(&desc->lock);
+ mutex_lock(&desc->rlock);
+ mutex_lock(&desc->wlock);
kill_urbs(desc);
cancel_work_sync(&desc->rxwork);
- mutex_unlock(&desc->lock);
+ mutex_unlock(&desc->wlock);
+ mutex_unlock(&desc->rlock);
wake_up_all(&desc->wait);
if (!desc->count)
cleanup(desc);
@@ -800,8 +807,10 @@ static int wdm_suspend(struct usb_interf
dev_dbg(&desc->intf->dev, "wdm%d_suspend\n", intf->minor);

/* if this is an autosuspend the caller does the locking */
- if (!(message.event & PM_EVENT_AUTO))
- mutex_lock(&desc->lock);
+ if (!(message.event & PM_EVENT_AUTO)) {
+ mutex_lock(&desc->rlock);
+ mutex_lock(&desc->wlock);
+ }
spin_lock_irq(&desc->iuspin);

if ((message.event & PM_EVENT_AUTO) &&
@@ -817,8 +826,10 @@ static int wdm_suspend(struct usb_interf
kill_urbs(desc);
cancel_work_sync(&desc->rxwork);
}
- if (!(message.event & PM_EVENT_AUTO))
- mutex_unlock(&desc->lock);
+ if (!(message.event & PM_EVENT_AUTO)) {
+ mutex_unlock(&desc->wlock);
+ mutex_unlock(&desc->rlock);
+ }

return rv;
}
@@ -856,7 +867,8 @@ static int wdm_pre_reset(struct usb_inte
{
struct wdm_device *desc = usb_get_intfdata(intf);

- mutex_lock(&desc->lock);
+ mutex_lock(&desc->rlock);
+ mutex_lock(&desc->wlock);
kill_urbs(desc);

/*
@@ -878,7 +890,8 @@ static int wdm_post_reset(struct usb_int
int rv;

rv = recover_from_urb_loss(desc);
- mutex_unlock(&desc->lock);
+ mutex_unlock(&desc->wlock);
+ mutex_unlock(&desc->rlock);
return 0;
}


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