[PATCH v6 3/3] btrfs: consolidate device_list_mutex in prepare_sprout to its parent
From: Anand Jain <hidden>
Date: 2021-09-21 04:33:58
Subsystem:
btrfs file system, filesystems (vfs and infrastructure), the rest · Maintainers:
Chris Mason, David Sterba, Alexander Viro, Christian Brauner, Linus Torvalds
btrfs_prepare_sprout() splices seed devices into its own struct fs_devices, so that its parent function btrfs_init_new_device() can add the new sprout device to fs_info->fs_devices. Both btrfs_prepare_sprout() and btrfs_init_new_device() needs device_list_mutex. But they are holding it sequentially, thus creates a small window to an opportunity to race. Close this opportunity and hold device_list_mutex common to both btrfs_init_new_device() and btrfs_prepare_sprout(). This patch splits btrfs_prepare_sprout() into btrfs_alloc_sprout() and btrfs_splice_sprout(). This split is essential because device_list_mutex shouldn't be held for btrfs_alloc_sprout() but must be held for btrfs_splice_sprout(). So now a common device_list_mutex can be used between btrfs_init_new_device() and btrfs_splice_sprout(). This patch also moves the lockdep_assert_held(&uuid_mutex) from the starting of the function to just above the line where we need this lock. Signed-off-by: Anand Jain <redacted> --- v6: Remove RFC. Split btrfs_prepare_sprout so that the allocation part can be outside of the device_list_mutex in the parent function btrfs_init_new_device(). fs/btrfs/volumes.c | 46 +++++++++++++++++++++++++++++++--------------- 1 file changed, 31 insertions(+), 15 deletions(-)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index e4079e25db70..b21eac32ec98 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c@@ -2376,19 +2376,13 @@ struct btrfs_device *btrfs_find_device_by_devspec( return btrfs_find_device_by_path(fs_info, device_path); } -/* - * does all the dirty work required for changing file system's UUID. - */ -static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) +static int btrfs_alloc_sprout(struct btrfs_fs_info *fs_info, + struct btrfs_fs_devices **seed_devices_ret) { struct btrfs_fs_devices *fs_devices = fs_info->fs_devices; struct btrfs_fs_devices *old_devices; struct btrfs_fs_devices *seed_devices; - struct btrfs_super_block *disk_super = fs_info->super_copy; - struct btrfs_device *device; - u64 super_flags; - lockdep_assert_held(&uuid_mutex); if (!fs_devices->seeding) return -EINVAL;
@@ -2412,6 +2406,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) return PTR_ERR(old_devices); } + lockdep_assert_held(&uuid_mutex); list_add(&old_devices->fs_list, &fs_uuids); memcpy(seed_devices, fs_devices, sizeof(*seed_devices));
@@ -2419,7 +2414,23 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) INIT_LIST_HEAD(&seed_devices->devices); INIT_LIST_HEAD(&seed_devices->alloc_list); - mutex_lock(&fs_devices->device_list_mutex); + *seed_devices_ret = seed_devices; + + return 0; +} + +/* + * Splice seed devices into the sprout fs_devices. + * Generate a new fsid for the sprouted readwrite btrfs. + */ +static void btrfs_splice_sprout(struct btrfs_fs_info *fs_info, + struct btrfs_fs_devices *seed_devices) +{ + struct btrfs_fs_devices *fs_devices = fs_info->fs_devices; + struct btrfs_super_block *disk_super = fs_info->super_copy; + struct btrfs_device *device; + u64 super_flags; + list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices, synchronize_rcu); list_for_each_entry(device, &seed_devices->devices, dev_list)
@@ -2435,13 +2446,10 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) generate_random_uuid(fs_devices->fsid); memcpy(fs_devices->metadata_uuid, fs_devices->fsid, BTRFS_FSID_SIZE); memcpy(disk_super->fsid, fs_devices->fsid, BTRFS_FSID_SIZE); - mutex_unlock(&fs_devices->device_list_mutex); super_flags = btrfs_super_flags(disk_super) & ~BTRFS_SUPER_FLAG_SEEDING; btrfs_set_super_flags(disk_super, super_flags); - - return 0; } /*
@@ -2529,6 +2537,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path struct super_block *sb = fs_info->sb; struct rcu_string *name; struct btrfs_fs_devices *fs_devices = fs_info->fs_devices; + struct btrfs_fs_devices *seed_devices; u64 orig_super_total_bytes; u64 orig_super_num_devices; int ret = 0;
@@ -2612,18 +2621,25 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path if (seeding_dev) { btrfs_clear_sb_rdonly(sb); - ret = btrfs_prepare_sprout(fs_info); + + /* GFP_KERNEL alloc should not be under device_list_mutex */ + ret = btrfs_alloc_sprout(fs_info, &seed_devices); if (ret) { btrfs_abort_transaction(trans, ret); goto error_trans; } + } + + mutex_lock(&fs_devices->device_list_mutex); + if (seeding_dev) { + btrfs_splice_sprout(fs_info, seed_devices); + btrfs_assign_next_active_device(fs_info->fs_devices->latest_dev, device); } device->fs_devices = fs_devices; - mutex_lock(&fs_devices->device_list_mutex); mutex_lock(&fs_info->chunk_mutex); list_add_rcu(&device->dev_list, &fs_devices->devices); list_add(&device->dev_alloc_list, &fs_devices->alloc_list);
@@ -2685,7 +2701,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path /* * fs_devices now represents the newly sprouted filesystem and - * its fsid has been changed by btrfs_prepare_sprout + * its fsid has been changed by btrfs_sprout_splice(). */ btrfs_sysfs_update_sprout_fsid(fs_devices); }
--
2.31.1