From: Anand Jain <anand.jain@oracle.com>
To: linux-btrfs@vger.kernel.org, dsterba@suse.com
Subject: [PATCH v6 3/3] btrfs: consolidate device_list_mutex in prepare_sprout to its parent
Date: Tue, 21 Sep 2021 12:33:25 +0800 [thread overview]
Message-ID: <ec3ecca596bf5d9de5e152942a277ab48915f0cf.1632179897.git.anand.jain@oracle.com> (raw)
In-Reply-To: <cover.1632179897.git.anand.jain@oracle.com>
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 <anand.jain@oracle.com>
---
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
next prev parent reply other threads:[~2021-09-21 4:33 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-21 4:33 [PATCH v6 0/3] btrfs: cleanup prepare_sprout Anand Jain
2021-09-21 4:33 ` [PATCH v6 1/3] btrfs: declare seeding_dev in init_new_device as bool Anand Jain
2021-09-21 11:01 ` Nikolay Borisov
2021-10-13 8:00 ` Anand Jain
2021-10-28 4:39 ` Anand Jain
2021-11-08 20:06 ` David Sterba
2021-09-21 4:33 ` [PATCH v6 2/3] btrfs: remove unused device_list_mutex for seed fs_devices Anand Jain
2021-09-21 6:44 ` Nikolay Borisov
2021-09-22 11:29 ` Anand Jain
2021-09-21 4:33 ` Anand Jain [this message]
2021-09-21 11:01 ` [PATCH v6 3/3] btrfs: consolidate device_list_mutex in prepare_sprout to its parent Nikolay Borisov
2021-09-22 11:41 ` Anand Jain
2021-09-23 6:52 ` Nikolay Borisov
2021-09-23 11:55 ` Anand Jain
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