[dpdk-dev] bus/vdev: reduce scope of device list lock
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Commit Message
The lock vdev_device_list_lock was taken before calling
"remove" function for the device.
So it prevents to remove sub-devices (as in failsafe) inside
its own "remove" function, because of a deadlock.
The lock is now only protecting the device list inside
the bus driver.
Fixes: 35f462839b69 ("bus/vdev: add lock on device list")
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
---
drivers/bus/vdev/vdev.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
Comments
On 21-May-18 5:11 PM, Thomas Monjalon wrote:
> The lock vdev_device_list_lock was taken before calling
> "remove" function for the device.
> So it prevents to remove sub-devices (as in failsafe) inside
> its own "remove" function, because of a deadlock.
>
> The lock is now only protecting the device list inside
> the bus driver.
>
> Fixes: 35f462839b69 ("bus/vdev: add lock on device list")
>
> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> ---
> drivers/bus/vdev/vdev.c | 10 ++++------
> 1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/bus/vdev/vdev.c b/drivers/bus/vdev/vdev.c
> index 099b9ff85..2fbc86806 100644
> --- a/drivers/bus/vdev/vdev.c
> +++ b/drivers/bus/vdev/vdev.c
> @@ -293,25 +293,23 @@ rte_vdev_uninit(const char *name)
> if (name == NULL)
> return -EINVAL;
>
> - rte_spinlock_lock(&vdev_device_list_lock);
> -
> dev = find_vdev(name);
> if (!dev) {
> ret = -ENOENT;
> - goto unlock;
> + return ret;
> }
Without that lock, all of this would be racy - find_dev would iterate a
tailq that might change under its feet, and tailq_remove may be called
with a pointer that has already been removed.
How about changing the lock to a recursive lock? Failsafe would be
removing devices from within the same thread, correct?
>
> ret = vdev_remove_driver(dev);
> if (ret)
> - goto unlock;
> + return ret;
>
> + rte_spinlock_lock(&vdev_device_list_lock);
> TAILQ_REMOVE(&vdev_device_list, dev, next);
> devargs = dev->device.devargs;
> rte_devargs_remove(devargs->bus->name, devargs->name);
> free(dev);
> -
> -unlock:
> rte_spinlock_unlock(&vdev_device_list_lock);
> +
> return ret;
> }
>
>
22/05/2018 11:05, Burakov, Anatoly:
> On 21-May-18 5:11 PM, Thomas Monjalon wrote:
> > The lock vdev_device_list_lock was taken before calling
> > "remove" function for the device.
> > So it prevents to remove sub-devices (as in failsafe) inside
> > its own "remove" function, because of a deadlock.
> >
> > The lock is now only protecting the device list inside
> > the bus driver.
> >
> > Fixes: 35f462839b69 ("bus/vdev: add lock on device list")
> >
> > Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
>
> Without that lock, all of this would be racy - find_dev would iterate a
> tailq that might change under its feet, and tailq_remove may be called
> with a pointer that has already been removed.
>
> How about changing the lock to a recursive lock? Failsafe would be
> removing devices from within the same thread, correct?
Yes it could work.
I will give it a try.
@@ -293,25 +293,23 @@ rte_vdev_uninit(const char *name)
if (name == NULL)
return -EINVAL;
- rte_spinlock_lock(&vdev_device_list_lock);
-
dev = find_vdev(name);
if (!dev) {
ret = -ENOENT;
- goto unlock;
+ return ret;
}
ret = vdev_remove_driver(dev);
if (ret)
- goto unlock;
+ return ret;
+ rte_spinlock_lock(&vdev_device_list_lock);
TAILQ_REMOVE(&vdev_device_list, dev, next);
devargs = dev->device.devargs;
rte_devargs_remove(devargs->bus->name, devargs->name);
free(dev);
-
-unlock:
rte_spinlock_unlock(&vdev_device_list_lock);
+
return ret;
}