On Wed, 17 Jul 2013 16:29:05 +0800, Anand Jain wrote:
> 'btrfs fi label /btrfs' will hang until balance is completed.
> (and probably even set label would hang). This is because we
> are trying to hold volume_mutex lock which balance will hold
> during its tenure.
>
> -------
> static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
> ::
> mutex_lock(&root->fs_info->volume_mutex);
> ret = copy_to_user(arg, label, len);
> mutex_unlock(&root->fs_info->volume_mutex);
> --------
>
> I doubt if get label would need such a heavy weight lock?
> Do we have any other lock which could fit better here ?
> Any comments ?
Just use the uuid_mutex instead of the volume_mutex.
In addition to the btrfs_ioctl_get_fslabel() and
btrfs_ioctl_set_fslabel() functions, only btrfs_scan_one_device()
accesses the label. And btrfs_scan_one_device() holds the uuid_mutex,
not the volume_mutex. You can do the same.
And since cwillu's commit 1332a002b, the uuid_mutex is not hold for a
long time anymore.
And while you change it, please move the mutex_lock() so that it
includes also the strnlen() access to the label, like this:
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 2177bea..30a8126 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4043,15 +4043,16 @@ static int btrfs_ioctl_get_fslabel(struct file
*file, vo
{
struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
const char *label = root->fs_info->super_copy->label;
- size_t len = strnlen(label, BTRFS_LABEL_SIZE);
+ size_t len;
int ret;
+ mutex_lock(&root->fs_info->volume_mutex);
+ len = strnlen(label, BTRFS_LABEL_SIZE);
if (len == BTRFS_LABEL_SIZE) {
pr_warn("btrfs: label is too long, return the first %zu
bytes\n"
--len);
}
- mutex_lock(&root->fs_info->volume_mutex);
ret = copy_to_user(arg, label, len);
mutex_unlock(&root->fs_info->volume_mutex);
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
