From 1f78160ce1b1b8e657e2248118c4d91f881763f0 Mon Sep 17 00:00:00 2001 From: Xiao Guangrong Date: Wed, 20 Apr 2011 10:09:16 +0000 Subject: [PATCH] Btrfs: using rcu lock in the reader side of devices list fs_devices->devices is only updated on remove and add device paths, so we can use rcu to protect it in the reader side Signed-off-by: Xiao Guangrong Signed-off-by: Chris Mason --- fs/btrfs/disk-io.c | 14 ++++---- fs/btrfs/ioctl.c | 7 ++-- fs/btrfs/volumes.c | 85 ++++++++++++++++++++++++++++++++-------------- fs/btrfs/volumes.h | 2 ++ 4 files changed, 72 insertions(+), 36 deletions(-) diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index 4e53a4fc467f..deba3d9c8853 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -1410,8 +1410,8 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits) struct btrfs_device *device; struct backing_dev_info *bdi; - mutex_lock(&info->fs_devices->device_list_mutex); - list_for_each_entry(device, &info->fs_devices->devices, dev_list) { + rcu_read_lock(); + list_for_each_entry_rcu(device, &info->fs_devices->devices, dev_list) { if (!device->bdev) continue; bdi = blk_get_backing_dev_info(device->bdev); @@ -1420,7 +1420,7 @@ static int btrfs_congested_fn(void *congested_data, int bdi_bits) break; } } - mutex_unlock(&info->fs_devices->device_list_mutex); + rcu_read_unlock(); return ret; } @@ -2332,9 +2332,9 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors) sb = &root->fs_info->super_for_commit; dev_item = &sb->dev_item; - mutex_lock(&root->fs_info->fs_devices->device_list_mutex); + rcu_read_lock(); head = &root->fs_info->fs_devices->devices; - list_for_each_entry(dev, head, dev_list) { + list_for_each_entry_rcu(dev, head, dev_list) { if (!dev->bdev) { total_errors++; continue; @@ -2367,7 +2367,7 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors) } total_errors = 0; - list_for_each_entry(dev, head, dev_list) { + list_for_each_entry_rcu(dev, head, dev_list) { if (!dev->bdev) continue; if (!dev->in_fs_metadata || !dev->writeable) @@ -2377,7 +2377,7 @@ int write_all_supers(struct btrfs_root *root, int max_mirrors) if (ret) total_errors++; } - mutex_unlock(&root->fs_info->fs_devices->device_list_mutex); + rcu_read_unlock(); if (total_errors > max_errors) { printk(KERN_ERR "btrfs: %d errors while writing supers\n", total_errors); diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index ce773fb736a1..0de71feb8e1c 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -281,8 +281,9 @@ static noinline int btrfs_ioctl_fitrim(struct file *file, void __user *arg) if (!capable(CAP_SYS_ADMIN)) return -EPERM; - mutex_lock(&fs_info->fs_devices->device_list_mutex); - list_for_each_entry(device, &fs_info->fs_devices->devices, dev_list) { + rcu_read_lock(); + list_for_each_entry_rcu(device, &fs_info->fs_devices->devices, + dev_list) { if (!device->bdev) continue; q = bdev_get_queue(device->bdev); @@ -292,7 +293,7 @@ static noinline int btrfs_ioctl_fitrim(struct file *file, void __user *arg) minlen); } } - mutex_unlock(&fs_info->fs_devices->device_list_mutex); + rcu_read_unlock(); if (!num_devices) return -EOPNOTSUPP; diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 0b5ca2737268..e7844f8a347a 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -363,7 +363,7 @@ static noinline int device_list_add(const char *path, INIT_LIST_HEAD(&device->dev_alloc_list); mutex_lock(&fs_devices->device_list_mutex); - list_add(&device->dev_list, &fs_devices->devices); + list_add_rcu(&device->dev_list, &fs_devices->devices); mutex_unlock(&fs_devices->device_list_mutex); device->fs_devices = fs_devices; @@ -471,6 +471,29 @@ again: return 0; } +static void __free_device(struct work_struct *work) +{ + struct btrfs_device *device; + + device = container_of(work, struct btrfs_device, rcu_work); + + if (device->bdev) + blkdev_put(device->bdev, device->mode); + + kfree(device->name); + kfree(device); +} + +static void free_device(struct rcu_head *head) +{ + struct btrfs_device *device; + + device = container_of(head, struct btrfs_device, rcu); + + INIT_WORK(&device->rcu_work, __free_device); + schedule_work(&device->rcu_work); +} + static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices) { struct btrfs_device *device; @@ -480,18 +503,27 @@ static int __btrfs_close_devices(struct btrfs_fs_devices *fs_devices) mutex_lock(&fs_devices->device_list_mutex); list_for_each_entry(device, &fs_devices->devices, dev_list) { - if (device->bdev) { - blkdev_put(device->bdev, device->mode); + struct btrfs_device *new_device; + + if (device->bdev) fs_devices->open_devices--; - } + if (device->writeable) { list_del_init(&device->dev_alloc_list); fs_devices->rw_devices--; } - device->bdev = NULL; - device->writeable = 0; - device->in_fs_metadata = 0; + new_device = kmalloc(sizeof(*new_device), GFP_NOFS); + BUG_ON(!new_device); + memcpy(new_device, device, sizeof(*new_device)); + new_device->name = kstrdup(device->name, GFP_NOFS); + BUG_ON(!new_device->name); + new_device->bdev = NULL; + new_device->writeable = 0; + new_device->in_fs_metadata = 0; + list_replace_rcu(&device->dev_list, &new_device->dev_list); + + call_rcu(&device->rcu, free_device); } mutex_unlock(&fs_devices->device_list_mutex); @@ -1204,11 +1236,13 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) struct block_device *bdev; struct buffer_head *bh = NULL; struct btrfs_super_block *disk_super; + struct btrfs_fs_devices *cur_devices; u64 all_avail; u64 devid; u64 num_devices; u8 *dev_uuid; int ret = 0; + bool clear_super = false; mutex_lock(&uuid_mutex); mutex_lock(&root->fs_info->volume_mutex); @@ -1294,6 +1328,7 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) list_del_init(&device->dev_alloc_list); unlock_chunks(root); root->fs_info->fs_devices->rw_devices--; + clear_super = true; } ret = btrfs_shrink_device(device, 0); @@ -1304,16 +1339,15 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) if (ret) goto error_undo; - device->in_fs_metadata = 0; - /* * the device list mutex makes sure that we don't change * the device list while someone else is writing out all * the device supers. */ + + cur_devices = device->fs_devices; mutex_lock(&root->fs_info->fs_devices->device_list_mutex); - list_del_init(&device->dev_list); - mutex_unlock(&root->fs_info->fs_devices->device_list_mutex); + list_del_rcu(&device->dev_list); device->fs_devices->num_devices--; @@ -1327,36 +1361,36 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) if (device->bdev == root->fs_info->fs_devices->latest_bdev) root->fs_info->fs_devices->latest_bdev = next_device->bdev; - if (device->bdev) { - blkdev_put(device->bdev, device->mode); - device->bdev = NULL; + if (device->bdev) device->fs_devices->open_devices--; - } + + call_rcu(&device->rcu, free_device); + mutex_unlock(&root->fs_info->fs_devices->device_list_mutex); num_devices = btrfs_super_num_devices(&root->fs_info->super_copy) - 1; btrfs_set_super_num_devices(&root->fs_info->super_copy, num_devices); - if (device->fs_devices->open_devices == 0) { + if (cur_devices->open_devices == 0) { struct btrfs_fs_devices *fs_devices; fs_devices = root->fs_info->fs_devices; while (fs_devices) { - if (fs_devices->seed == device->fs_devices) + if (fs_devices->seed == cur_devices) break; fs_devices = fs_devices->seed; } - fs_devices->seed = device->fs_devices->seed; - device->fs_devices->seed = NULL; + fs_devices->seed = cur_devices->seed; + cur_devices->seed = NULL; lock_chunks(root); - __btrfs_close_devices(device->fs_devices); + __btrfs_close_devices(cur_devices); unlock_chunks(root); - free_fs_devices(device->fs_devices); + free_fs_devices(cur_devices); } /* * at this point, the device is zero sized. We want to * remove it from the devices list and zero out the old super */ - if (device->writeable) { + if (clear_super) { /* make sure this device isn't detected as part of * the FS anymore */ @@ -1365,8 +1399,6 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) sync_dirty_buffer(bh); } - kfree(device->name); - kfree(device); ret = 0; error_brelse: @@ -1425,7 +1457,8 @@ static int btrfs_prepare_sprout(struct btrfs_trans_handle *trans, mutex_init(&seed_devices->device_list_mutex); mutex_lock(&root->fs_info->fs_devices->device_list_mutex); - list_splice_init(&fs_devices->devices, &seed_devices->devices); + list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices, + synchronize_rcu); mutex_unlock(&root->fs_info->fs_devices->device_list_mutex); list_splice_init(&fs_devices->alloc_list, &seed_devices->alloc_list); @@ -1624,7 +1657,7 @@ int btrfs_init_new_device(struct btrfs_root *root, char *device_path) * half setup */ mutex_lock(&root->fs_info->fs_devices->device_list_mutex); - list_add(&device->dev_list, &root->fs_info->fs_devices->devices); + list_add_rcu(&device->dev_list, &root->fs_info->fs_devices->devices); list_add(&device->dev_alloc_list, &root->fs_info->fs_devices->alloc_list); root->fs_info->fs_devices->num_devices++; diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h index cc2eadaf7a27..f1b2e4f53fc2 100644 --- a/fs/btrfs/volumes.h +++ b/fs/btrfs/volumes.h @@ -86,6 +86,8 @@ struct btrfs_device { u8 uuid[BTRFS_UUID_SIZE]; struct btrfs_work work; + struct rcu_head rcu; + struct work_struct rcu_work; }; struct btrfs_fs_devices { -- 2.30.2