From: Anand Jain <anand.jain@oracle.com>
Date: Tue, 9 Nov 2021 09:51:58 +0000 (+0800)
Subject: btrfs: consolidate device_list_mutex in prepare_sprout to its parent
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=849eae5e57a703105aa6cdce0d860ab95f44d81c;p=linux.git
btrfs: consolidate device_list_mutex in prepare_sprout to its parent
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() need
device_list_mutex. But they are holding it separately, thus create a
small race window. Close it and hold device_list_mutex across both
functions btrfs_init_new_device() and btrfs_prepare_sprout().
Split btrfs_prepare_sprout() into btrfs_init_sprout() and
btrfs_setup_sprout(). This split is essential because device_list_mutex
must not be held for allocations in btrfs_init_sprout() but must be held
for btrfs_setup_sprout(). So now a common device_list_mutex can be used
between btrfs_init_new_device() and btrfs_setup_sprout().
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 836e1b661fc9..53753e04af14 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2431,21 +2431,15 @@ struct btrfs_device *btrfs_find_device_by_devspec(
return device;
}
-/*
- * does all the dirty work required for changing file system's UUID.
- */
-static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
+static struct btrfs_fs_devices *btrfs_init_sprout(struct btrfs_fs_info *fs_info)
{
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;
+ return ERR_PTR(-EINVAL);
/*
* Private copy of the seed devices, anchored at
@@ -2453,7 +2447,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
*/
seed_devices = alloc_fs_devices(NULL, NULL);
if (IS_ERR(seed_devices))
- return PTR_ERR(seed_devices);
+ return seed_devices;
/*
* It's necessary to retain a copy of the original seed fs_devices in
@@ -2464,7 +2458,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
old_devices = clone_fs_devices(fs_devices);
if (IS_ERR(old_devices)) {
kfree(seed_devices);
- return PTR_ERR(old_devices);
+ return old_devices;
}
list_add(&old_devices->fs_list, &fs_uuids);
@@ -2475,7 +2469,41 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
INIT_LIST_HEAD(&seed_devices->alloc_list);
mutex_init(&seed_devices->device_list_mutex);
- mutex_lock(&fs_devices->device_list_mutex);
+ return seed_devices;
+}
+
+/*
+ * Splice seed devices into the sprout fs_devices.
+ * Generate a new fsid for the sprouted read-write filesystem.
+ */
+static void btrfs_setup_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;
+
+ /*
+ * We are updating the fsid, the thread leading to device_list_add()
+ * could race, so uuid_mutex is needed.
+ */
+ lockdep_assert_held(&uuid_mutex);
+
+ /*
+ * The threads listed below may traverse dev_list but can do that without
+ * device_list_mutex:
+ * - All device ops and balance - as we are in btrfs_exclop_start.
+ * - Various dev_list readers - are using RCU.
+ * - btrfs_ioctl_fitrim() - is using RCU.
+ *
+ * For-read threads as below are using device_list_mutex:
+ * - Readonly scrub btrfs_scrub_dev()
+ * - Readonly scrub btrfs_scrub_progress()
+ * - btrfs_get_dev_stats()
+ */
+ lockdep_assert_held(&fs_devices->device_list_mutex);
+
list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices,
synchronize_rcu);
list_for_each_entry(device, &seed_devices->devices, dev_list)
@@ -2491,13 +2519,10 @@ 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;
}
/*
@@ -2588,6 +2613,7 @@ 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;
@@ -2671,18 +2697,25 @@ 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);
- if (ret) {
+
+ /* GFP_KERNEL allocation must not be under device_list_mutex */
+ seed_devices = btrfs_init_sprout(fs_info);
+ if (IS_ERR(seed_devices)) {
+ ret = PTR_ERR(seed_devices);
btrfs_abort_transaction(trans, ret);
goto error_trans;
}
+ }
+
+ mutex_lock(&fs_devices->device_list_mutex);
+ if (seeding_dev) {
+ btrfs_setup_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);
@@ -2744,7 +2777,7 @@ 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);
}