On Sun, Nov 30, 2014 at 3:26 AM, Omar Sandoval <osan...@osandov.com> wrote:
> A naked read of the value of an RCU pointer isn't safe. Put the whole access
> in
> an RCU critical section, not just the pointer dereference.
>
> Signed-off-by: Omar Sandoval <osan...@osandov.com>
You can use rcu_access_pointer() in the if() condition check rather
than increasing the read critical section. We should try to keep the
critical section as small as possible.
Also, since we have rcu_str_deref() we can use that instead of
rcu_dereference() on device->name. Thoughts?
> ---
> fs/btrfs/ioctl.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index ecdf68f..dd55844 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2706,6 +2706,7 @@ static long btrfs_ioctl_dev_info(struct btrfs_root
> *root, void __user *arg)
> struct btrfs_fs_devices *fs_devices = root->fs_info->fs_devices;
> int ret = 0;
> char *s_uuid = NULL;
> + struct rcu_string *name;
>
> di_args = memdup_user(arg, sizeof(*di_args));
> if (IS_ERR(di_args))
> @@ -2726,17 +2727,16 @@ static long btrfs_ioctl_dev_info(struct btrfs_root
> *root, void __user *arg)
> di_args->bytes_used = btrfs_device_get_bytes_used(dev);
> di_args->total_bytes = btrfs_device_get_total_bytes(dev);
> memcpy(di_args->uuid, dev->uuid, sizeof(di_args->uuid));
> - if (dev->name) {
> - struct rcu_string *name;
>
> - rcu_read_lock();
> - name = rcu_dereference(dev->name);
> + rcu_read_lock();
> + name = rcu_dereference(dev->name);
> + if (name) {
> strncpy(di_args->path, name->str, sizeof(di_args->path));
> - rcu_read_unlock();
> di_args->path[sizeof(di_args->path) - 1] = 0;
> } else {
> di_args->path[0] = '\0';
> }
> + rcu_read_unlock();
>
> out:
> mutex_unlock(&fs_devices->device_list_mutex);
> --
> 2.1.3
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majord...@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
