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Btrfs: fix race between balance and unused block group deletion
We have a race between deleting an unused block group and balancing the same block group that leads to an assertion failure/BUG(), producing the following trace: [181631.208236] BTRFS: assertion failed: 0, file: fs/btrfs/volumes.c, line: 2622 [181631.220591] ------------[ cut here ]------------ [181631.222959] kernel BUG at fs/btrfs/ctree.h:4062! [181631.223932] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [181631.224566] Modules linked in: btrfs dm_flakey dm_mod crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace fscache sunrpc loop fuse acpi_cpufreq parpor$ [181631.224566] CPU: 8 PID: 17451 Comm: btrfs Tainted: G W 4.1.0-rc5-btrfs-next-10+ #1 [181631.224566] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014 [181631.224566] task: ffff880127e09590 ti: ffff8800b5824000 task.ti: ffff8800b5824000 [181631.224566] RIP: 0010:[<ffffffffa03f19f6>] [<ffffffffa03f19f6>] assfail.constprop.50+0x1e/0x20 [btrfs] [181631.224566] RSP: 0018:ffff8800b5827ae8 EFLAGS: 00010246 [181631.224566] RAX: 0000000000000040 RBX: ffff8800109fc218 RCX: ffffffff81095dce [181631.224566] RDX: 0000000000005124 RSI: ffffffff81464819 RDI: 00000000ffffffff [181631.224566] RBP: ffff8800b5827ae8 R08: 0000000000000001 R09: 0000000000000000 [181631.224566] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800109fc200 [181631.224566] R13: ffff880020095000 R14: ffff8800b1a13f38 R15: ffff880020095000 [181631.224566] FS: 00007f70ca0b0c80(0000) GS:ffff88013ec00000(0000) knlGS:0000000000000000 [181631.224566] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [181631.224566] CR2: 00007f2872ab6e68 CR3: 00000000a717c000 CR4: 00000000000006e0 [181631.224566] Stack: [181631.224566] ffff8800b5827ba8 ffffffffa03f3916 ffff8800b5827b38 ffffffffa03d080e [181631.224566] ffffffffa03d1423 ffff880020095000 ffff88001233c000 0000000000000001 [181631.224566] ffff880020095000 ffff8800b1a13f38 0000000a69c00000 0000000000000000 [181631.224566] Call Trace: [181631.224566] [<ffffffffa03f3916>] btrfs_remove_chunk+0xa4/0x6bb [btrfs] [181631.224566] [<ffffffffa03d080e>] ? join_transaction.isra.8+0xb9/0x3ba [btrfs] [181631.224566] [<ffffffffa03d1423>] ? wait_current_trans.isra.13+0x22/0xfc [btrfs] [181631.224566] [<ffffffffa03f3fbc>] btrfs_relocate_chunk.isra.29+0x8f/0xa7 [btrfs] [181631.224566] [<ffffffffa03f54df>] btrfs_balance+0xaa4/0xc52 [btrfs] [181631.224566] [<ffffffffa03fd388>] btrfs_ioctl_balance+0x23f/0x2b0 [btrfs] [181631.224566] [<ffffffff810872f9>] ? trace_hardirqs_on+0xd/0xf [181631.224566] [<ffffffffa04019a3>] btrfs_ioctl+0xfe2/0x2220 [btrfs] [181631.224566] [<ffffffff812603ed>] ? __this_cpu_preempt_check+0x13/0x15 [181631.224566] [<ffffffff81084669>] ? arch_local_irq_save+0x9/0xc [181631.224566] [<ffffffff81138def>] ? handle_mm_fault+0x834/0xcd2 [181631.224566] [<ffffffff81138def>] ? handle_mm_fault+0x834/0xcd2 [181631.224566] [<ffffffff8103e48c>] ? __do_page_fault+0x211/0x424 [181631.224566] [<ffffffff811755e6>] do_vfs_ioctl+0x3c6/0x479 (...) The sequence of steps leading to this are: CPU 0 CPU 1 btrfs_balance() btrfs_relocate_chunk() btrfs_relocate_block_group(bg X) btrfs_lookup_block_group(bg X) cleaner_kthread locks fs_info->cleaner_mutex btrfs_delete_unused_bgs() finds bg X, which became unused in the previous transaction checks bg X ->ro == 0, so it proceeds sets bg X ->ro to 1 (btrfs_set_block_group_ro(bg X)) blocks on fs_info->cleaner_mutex btrfs_remove_chunk(bg X) unlocks fs_info->cleaner_mutex acquires fs_info->cleaner_mutex relocate_block_group() --> does nothing, no extents found in the extent tree from bg X unlocks fs_info->cleaner_mutex btrfs_relocate_block_group(bg X) returns btrfs_remove_chunk(bg X) extent map not found --> ASSERT(0) Fix this by using a new mutex to make sure these 2 operations, block group relocation and removal, are serialized. This issue is reproducible by running fstests generic/038 (which stresses chunk allocation and automatic removal of unused block groups) together with the following balance loop: while true; do btrfs balance start -dusage=0 <mountpoint> ; done Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Filipe Manana
Chris Mason
parent
e82afc52ab
commit
67c5e7d464
@ -1778,6 +1778,7 @@ struct btrfs_fs_info {
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spinlock_t unused_bgs_lock;
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struct list_head unused_bgs;
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struct mutex unused_bg_unpin_mutex;
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struct mutex delete_unused_bgs_mutex;
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/* For btrfs to record security options */
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struct security_mnt_opts security_opts;
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@ -1772,7 +1772,6 @@ static int cleaner_kthread(void *arg)
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}
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btrfs_run_delayed_iputs(root);
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btrfs_delete_unused_bgs(root->fs_info);
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again = btrfs_clean_one_deleted_snapshot(root);
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mutex_unlock(&root->fs_info->cleaner_mutex);
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@ -1781,6 +1780,16 @@ static int cleaner_kthread(void *arg)
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* needn't do anything special here.
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*/
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btrfs_run_defrag_inodes(root->fs_info);
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/*
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* Acquires fs_info->delete_unused_bgs_mutex to avoid racing
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* with relocation (btrfs_relocate_chunk) and relocation
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* acquires fs_info->cleaner_mutex (btrfs_relocate_block_group)
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* after acquiring fs_info->delete_unused_bgs_mutex. So we
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* can't hold, nor need to, fs_info->cleaner_mutex when deleting
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* unused block groups.
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*/
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btrfs_delete_unused_bgs(root->fs_info);
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sleep:
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if (!try_to_freeze() && !again) {
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set_current_state(TASK_INTERRUPTIBLE);
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@ -2492,6 +2501,7 @@ int open_ctree(struct super_block *sb,
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spin_lock_init(&fs_info->unused_bgs_lock);
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rwlock_init(&fs_info->tree_mod_log_lock);
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mutex_init(&fs_info->unused_bg_unpin_mutex);
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mutex_init(&fs_info->delete_unused_bgs_mutex);
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mutex_init(&fs_info->reloc_mutex);
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mutex_init(&fs_info->delalloc_root_mutex);
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seqlock_init(&fs_info->profiles_lock);
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@ -9889,6 +9889,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
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}
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spin_unlock(&fs_info->unused_bgs_lock);
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mutex_lock(&root->fs_info->delete_unused_bgs_mutex);
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/* Don't want to race with allocators so take the groups_sem */
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down_write(&space_info->groups_sem);
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spin_lock(&block_group->lock);
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@ -9983,6 +9985,7 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
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end_trans:
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btrfs_end_transaction(trans, root);
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next:
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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btrfs_put_block_group(block_group);
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spin_lock(&fs_info->unused_bgs_lock);
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}
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@ -2766,6 +2766,20 @@ static int btrfs_relocate_chunk(struct btrfs_root *root,
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root = root->fs_info->chunk_root;
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extent_root = root->fs_info->extent_root;
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/*
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* Prevent races with automatic removal of unused block groups.
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* After we relocate and before we remove the chunk with offset
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* chunk_offset, automatic removal of the block group can kick in,
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* resulting in a failure when calling btrfs_remove_chunk() below.
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*
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* Make sure to acquire this mutex before doing a tree search (dev
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* or chunk trees) to find chunks. Otherwise the cleaner kthread might
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* call btrfs_remove_chunk() (through btrfs_delete_unused_bgs()) after
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* we release the path used to search the chunk/dev tree and before
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* the current task acquires this mutex and calls us.
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*/
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ASSERT(mutex_is_locked(&root->fs_info->delete_unused_bgs_mutex));
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ret = btrfs_can_relocate(extent_root, chunk_offset);
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if (ret)
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return -ENOSPC;
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@ -2814,13 +2828,18 @@ static int btrfs_relocate_sys_chunks(struct btrfs_root *root)
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key.type = BTRFS_CHUNK_ITEM_KEY;
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while (1) {
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mutex_lock(&root->fs_info->delete_unused_bgs_mutex);
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ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
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if (ret < 0)
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if (ret < 0) {
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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goto error;
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}
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BUG_ON(ret == 0); /* Corruption */
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ret = btrfs_previous_item(chunk_root, path, key.objectid,
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key.type);
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if (ret)
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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if (ret < 0)
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goto error;
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if (ret > 0)
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@ -2843,6 +2862,7 @@ static int btrfs_relocate_sys_chunks(struct btrfs_root *root)
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else
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BUG_ON(ret);
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}
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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if (found_key.offset == 0)
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break;
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@ -3299,9 +3319,12 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
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goto error;
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}
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mutex_lock(&fs_info->delete_unused_bgs_mutex);
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ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
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if (ret < 0)
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if (ret < 0) {
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mutex_unlock(&fs_info->delete_unused_bgs_mutex);
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goto error;
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}
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/*
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* this shouldn't happen, it means the last relocate
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@ -3313,6 +3336,7 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
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ret = btrfs_previous_item(chunk_root, path, 0,
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BTRFS_CHUNK_ITEM_KEY);
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if (ret) {
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mutex_unlock(&fs_info->delete_unused_bgs_mutex);
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ret = 0;
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break;
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}
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@ -3321,8 +3345,10 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
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slot = path->slots[0];
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btrfs_item_key_to_cpu(leaf, &found_key, slot);
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if (found_key.objectid != key.objectid)
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if (found_key.objectid != key.objectid) {
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mutex_unlock(&fs_info->delete_unused_bgs_mutex);
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break;
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}
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chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
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@ -3335,10 +3361,13 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
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ret = should_balance_chunk(chunk_root, leaf, chunk,
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found_key.offset);
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btrfs_release_path(path);
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if (!ret)
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if (!ret) {
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mutex_unlock(&fs_info->delete_unused_bgs_mutex);
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goto loop;
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}
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if (counting) {
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mutex_unlock(&fs_info->delete_unused_bgs_mutex);
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spin_lock(&fs_info->balance_lock);
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bctl->stat.expected++;
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spin_unlock(&fs_info->balance_lock);
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@ -3348,6 +3377,7 @@ static int __btrfs_balance(struct btrfs_fs_info *fs_info)
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ret = btrfs_relocate_chunk(chunk_root,
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found_key.objectid,
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found_key.offset);
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mutex_unlock(&fs_info->delete_unused_bgs_mutex);
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if (ret && ret != -ENOSPC)
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goto error;
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if (ret == -ENOSPC) {
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@ -4087,11 +4117,16 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
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key.type = BTRFS_DEV_EXTENT_KEY;
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do {
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mutex_lock(&root->fs_info->delete_unused_bgs_mutex);
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ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
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if (ret < 0)
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if (ret < 0) {
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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goto done;
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}
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ret = btrfs_previous_item(root, path, 0, key.type);
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if (ret)
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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if (ret < 0)
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goto done;
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if (ret) {
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@ -4105,6 +4140,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
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btrfs_item_key_to_cpu(l, &key, path->slots[0]);
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if (key.objectid != device->devid) {
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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btrfs_release_path(path);
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break;
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}
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@ -4113,6 +4149,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
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length = btrfs_dev_extent_length(l, dev_extent);
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if (key.offset + length <= new_size) {
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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btrfs_release_path(path);
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break;
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}
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@ -4122,6 +4159,7 @@ int btrfs_shrink_device(struct btrfs_device *device, u64 new_size)
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btrfs_release_path(path);
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ret = btrfs_relocate_chunk(root, chunk_objectid, chunk_offset);
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mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
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if (ret && ret != -ENOSPC)
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goto done;
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if (ret == -ENOSPC)
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