From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: [PATCH 4/5] Btrfs: drop unnecessary device lock Date: Wed, 20 Apr 2011 18:08:47 +0800 Message-ID: <4DAEB0AF.6030306@cn.fujitsu.com> References: <4DAEB030.1070303@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Cc: LKML , BTRFS To: Chris Mason Return-path: In-Reply-To: <4DAEB030.1070303@cn.fujitsu.com> List-ID: Drop device_list_mutex for the reader side on clone_fs_devices and btrfs_rm_device pathes since the fs_info->volume_mutex can ensure the device list is not updated btrfs_close_extra_devices is the initialized path, we can not add or remove device at this time, so we can simply drop the mutex safely, like other initialized function does(add_missing_dev, __find_device, __btrfs_open_devices ...). Signed-off-by: Xiao Guangrong --- fs/btrfs/volumes.c | 13 ++++++------- 1 files changed, 6 insertions(+), 7 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index d20351f..f43b946 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -440,7 +440,7 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig) fs_devices->latest_trans = orig->latest_trans; memcpy(fs_devices->fsid, orig->fsid, sizeof(fs_devices->fsid)); - mutex_lock(&orig->device_list_mutex); + /* We have held the volume lock, it is safe to get the devices. */ list_for_each_entry(orig_dev, &orig->devices, dev_list) { device = kzalloc(sizeof(*device), GFP_NOFS); if (!device) @@ -463,10 +463,8 @@ static struct btrfs_fs_devices *clone_fs_devices(struct btrfs_fs_devices *orig) device->fs_devices = fs_devices; fs_devices->num_devices++; } - mutex_unlock(&orig->device_list_mutex); return fs_devices; error: - mutex_unlock(&orig->device_list_mutex); free_fs_devices(fs_devices); return ERR_PTR(-ENOMEM); } @@ -477,7 +475,7 @@ int btrfs_close_extra_devices(struct btrfs_fs_devices *fs_devices) mutex_lock(&uuid_mutex); again: - mutex_lock(&fs_devices->device_list_mutex); + /* This is the initialized path, it is safe to release the devices. */ list_for_each_entry_safe(device, next, &fs_devices->devices, dev_list) { if (device->in_fs_metadata) continue; @@ -497,7 +495,6 @@ again: kfree(device->name); kfree(device); } - mutex_unlock(&fs_devices->device_list_mutex); if (fs_devices->seed) { fs_devices = fs_devices->seed; @@ -1276,14 +1273,16 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) device = NULL; devices = &root->fs_info->fs_devices->devices; - mutex_lock(&root->fs_info->fs_devices->device_list_mutex); + /* + * It is safe to read the devices since the volume_mutex + * is held. + */ list_for_each_entry(tmp, devices, dev_list) { if (tmp->in_fs_metadata && !tmp->bdev) { device = tmp; break; } } - mutex_unlock(&root->fs_info->fs_devices->device_list_mutex); bdev = NULL; bh = NULL; disk_super = NULL; -- 1.7.4.4