[BUG] When a lot of subvolumes are created, there is a user report about transaction aborted: ------------[ cut here ]------------ BTRFS: Transaction aborted (error -24) WARNING: CPU: 17 PID: 17041 at fs/btrfs/transaction.c:1576 create_pending_snapshot+0xbc4/0xd10 [btrfs] RIP: 0010:create_pending_snapshot+0xbc4/0xd10 [btrfs] Call Trace: create_pending_snapshots+0x82/0xa0 [btrfs] btrfs_commit_transaction+0x275/0x8c0 [btrfs] btrfs_mksubvol+0x4b9/0x500 [btrfs] btrfs_ioctl_snap_create_transid+0x174/0x180 [btrfs] btrfs_ioctl_snap_create_v2+0x11c/0x180 [btrfs] btrfs_ioctl+0x11a4/0x2da0 [btrfs] do_vfs_ioctl+0xa9/0x640 ksys_ioctl+0x67/0x90 __x64_sys_ioctl+0x1a/0x20 do_syscall_64+0x5a/0x110 entry_SYSCALL_64_after_hwframe+0x44/0xa9 ---[ end trace 33f2f83f3d5250e9 ]--- BTRFS: error (device sda1) in create_pending_snapshot:1576: errno=-24 unknown BTRFS info (device sda1): forced readonly BTRFS warning (device sda1): Skipping commit of aborted transaction. BTRFS: error (device sda1) in cleanup_transaction:1831: errno=-24 unknown [CAUSE] The root cause is we don't have unlimited resource for anonymous block device number. The anonymous block device pool only contains 1<<20 devices, and is shared across a several fses, like ceph and overlayfs. While btrfs has support for 1<<48 subvolumes, so it's just a problem of time to hit such limit. [WORKAROUND] Here we can free btrfs_root::anon_dev as long as the subvolume is no longer visible to users. By freeing it earlier we reclaim the anon_dev quicker, hopefully to reduce the chance of exhausting the pool. Reported-by: Greed Rong <greedrong@xxxxxxxxx> Link: https://lore.kernel.org/linux-btrfs/CA+UqX+NTrZ6boGnWHhSeZmEY5J76CTqmYjO2S+=tHJX7nb9DPw@xxxxxxxxxxxxxx/ Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> --- fs/btrfs/inode.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 195aac71fe32..e9f5a166d056 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -4045,6 +4045,8 @@ int btrfs_delete_subvolume(struct inode *dir, struct dentry *dentry) } } + free_anon_bdev(dest->anon_dev); + dest->anon_dev = 0; out_end_trans: trans->block_rsv = NULL; trans->bytes_reserved = 0; -- 2.27.0
