The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 082b6c970f02fefd278c7833880cda29691a5f34 Mon Sep 17 00:00:00 2001 From: Qu Wenruo <wqu@xxxxxxxx> Date: Tue, 16 Jun 2020 10:17:37 +0800 Subject: [PATCH] btrfs: free anon block device right after subvolume deletion [BUG] When a lot of subvolumes are created, there is a user report about transaction aborted caused by slow anonymous block device reclaim: 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 anonymous device pool is shared and its size is 1M. It's possible to hit that limit if the subvolume deletion is not fast enough and the subvolumes to be cleaned keep the ids allocated. [WORKAROUND] We can't avoid the anon device pool exhaustion but we can shorten the time the id is attached to the subvolume root once the subvolume becomes invisible to the user. Reported-by: Greed Rong <greedrong@xxxxxxxxx> Link: https://lore.kernel.org/linux-btrfs/CA+UqX+NTrZ6boGnWHhSeZmEY5J76CTqmYjO2S+=tHJX7nb9DPw@xxxxxxxxxxxxxx/ CC: stable@xxxxxxxxxxxxxxx # 4.4+ Reviewed-by: Josef Bacik <josef@xxxxxxxxxxxxxx> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> Reviewed-by: David Sterba <dsterba@xxxxxxxx> Signed-off-by: David Sterba <dsterba@xxxxxxxx> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 5d2ce8092531..f066cad2d039 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -4026,6 +4026,8 @@ 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;
