[PATCH 04/12] btrfs: open block devices after superblock creation

Christoph Hellwig
2023-08-02T15:42:11Z

Currently btrfs_mount_root opens the block devices before committing to
allocating a super block. That creates problems for restricting the
number of writers to a device, and also leads to a unusual and not very
helpful holder (the fs_type).

Reorganize the code to first look whether the superblock for a
particular fsid does already exist and open the block devices only if it
doesn't, mirror the recent changes to the VFS mount helpers.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/btrfs/super.c | 51 ++++++++++++++++++++++------------------------
fs/btrfs/volumes.c | 4 ++--
2 files changed, 26 insertions(+), 29 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index b318bddefd5236..5980b5dcc6b163 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1434,10 +1434,8 @@ static struct dentry *mount_subvol(const char *subvol_name, u64 subvol_objectid,
static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
int flags, const char *device_name, void *data)
{
- struct block_device *bdev = NULL;
struct super_block *s;
struct btrfs_device *device = NULL;
- struct btrfs_fs_devices *fs_devices = NULL;
struct btrfs_fs_info *fs_info = NULL;
void *new_sec_opts = NULL;
int error = 0;
@@ -1483,35 +1481,36 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
error = PTR_ERR(device);
goto error_fs_info;
}
-
- fs_devices = device->fs_devices;
- fs_info->fs_devices = fs_devices;
-
- error = btrfs_open_devices(fs_devices, sb_open_mode(flags), fs_type);
+ fs_info->fs_devices = device->fs_devices;
mutex_unlock(&uuid_mutex);
- if (error)
- goto error_fs_info;
-
- if (!(flags & SB_RDONLY) && fs_devices->rw_devices == 0) {
- error = -EACCES;
- goto error_close_devices;
- }

- bdev = fs_devices->latest_dev->bdev;
s = sget(fs_type, btrfs_test_super, btrfs_set_super, flags | SB_NOSEC,
fs_info);
if (IS_ERR(s)) {
error = PTR_ERR(s);
- goto error_close_devices;
+ goto error_fs_info;
}

if (s->s_root) {
- btrfs_close_devices(fs_devices);
btrfs_free_fs_info(fs_info);
if ((flags ^ s->s_flags) & SB_RDONLY)
error = -EBUSY;
} else {
- snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
+ struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
+
+ error = btrfs_open_devices(fs_devices, sb_open_mode(flags),
+ fs_type);
+ if (error)
+ goto out_deactivate;
+
+ if (!(flags & SB_RDONLY) && fs_devices->rw_devices == 0) {
+ error = -EACCES;
+ btrfs_close_devices(fs_info->fs_devices);
+ goto out_deactivate;
+ }
+
+ snprintf(s->s_id, sizeof(s->s_id), "%pg",
+ fs_devices->latest_dev->bdev);
shrinker_debugfs_rename(&s->s_shrink, "sb-%s:%s", fs_type->name,
s->s_id);
btrfs_sb(s)->bdev_holder = fs_type;
@@ -1519,21 +1518,19 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
}
if (!error)
error = security_sb_set_mnt_opts(s, new_sec_opts, 0, NULL);
+ if (error)
+ goto out_deactivate;
security_free_mnt_opts(&new_sec_opts);
- if (error) {
- deactivate_locked_super(s);
- return ERR_PTR(error);
- }
-
return dget(s->s_root);

-error_close_devices:
- btrfs_close_devices(fs_devices);
-error_fs_info:
- btrfs_free_fs_info(fs_info);
+out_deactivate:
+ deactivate_locked_super(s);
error_sec_opts:
security_free_mnt_opts(&new_sec_opts);
return ERR_PTR(error);
+error_fs_info:
+ btrfs_free_fs_info(fs_info);
+ goto error_sec_opts;
}

/*
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 8246578c70f55b..88e9daae5e74ed 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1269,7 +1269,6 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
{
int ret;

- lockdep_assert_held(&uuid_mutex);
/*
* The device_list_mutex cannot be taken here in case opening the
* underlying device takes further locks like open_mutex.
@@ -1277,7 +1276,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
* We also don't need the lock here as this is called during mount and
* exclusion is provided by uuid_mutex
*/
-
+ mutex_lock(&uuid_mutex);
if (fs_devices->opened) {
fs_devices->opened++;
ret = 0;
@@ -1285,6 +1284,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
list_sort(NULL, &fs_devices->devices, devid_cmp);
ret = open_fs_devices(fs_devices, flags, holder);
}
+ mutex_unlock(&uuid_mutex);

return ret;
}
--
2.39.2