From 67c5e7d464bc466471b05e027abe8a6b29687ebd Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Thu, 11 Jun 2015 00:58:53 +0100 Subject: [PATCH] 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:[] [] 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] [] btrfs_remove_chunk+0xa4/0x6bb [btrfs] [181631.224566] [] ? join_transaction.isra.8+0xb9/0x3ba [btrfs] [181631.224566] [] ? wait_current_trans.isra.13+0x22/0xfc [btrfs] [181631.224566] [] btrfs_relocate_chunk.isra.29+0x8f/0xa7 [btrfs] [181631.224566] [] btrfs_balance+0xaa4/0xc52 [btrfs] [181631.224566] [] btrfs_ioctl_balance+0x23f/0x2b0 [btrfs] [181631.224566] [] ? trace_hardirqs_on+0xd/0xf [181631.224566] [] btrfs_ioctl+0xfe2/0x2220 [btrfs] [181631.224566] [] ? __this_cpu_preempt_check+0x13/0x15 [181631.224566] [] ? arch_local_irq_save+0x9/0xc [181631.224566] [] ? handle_mm_fault+0x834/0xcd2 [181631.224566] [] ? handle_mm_fault+0x834/0xcd2 [181631.224566] [] ? __do_page_fault+0x211/0x424 [181631.224566] [] 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 ; done Signed-off-by: Filipe Manana Signed-off-by: Chris Mason --- fs/btrfs/ctree.h | 1 + fs/btrfs/disk-io.c | 12 ++++++++++- fs/btrfs/extent-tree.c | 3 +++ fs/btrfs/volumes.c | 48 +++++++++++++++++++++++++++++++++++++----- 4 files changed, 58 insertions(+), 6 deletions(-) diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 80a9aefb0c46..aac314e14188 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -1778,6 +1778,7 @@ struct btrfs_fs_info { spinlock_t unused_bgs_lock; struct list_head unused_bgs; struct mutex unused_bg_unpin_mutex; + struct mutex delete_unused_bgs_mutex; /* For btrfs to record security options */ struct security_mnt_opts security_opts; diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c index b977fc8d8201..b59deb2c63f4 100644 --- a/fs/btrfs/disk-io.c +++ b/fs/btrfs/disk-io.c @@ -1772,7 +1772,6 @@ static int cleaner_kthread(void *arg) } btrfs_run_delayed_iputs(root); - btrfs_delete_unused_bgs(root->fs_info); again = btrfs_clean_one_deleted_snapshot(root); mutex_unlock(&root->fs_info->cleaner_mutex); @@ -1781,6 +1780,16 @@ static int cleaner_kthread(void *arg) * needn't do anything special here. */ btrfs_run_defrag_inodes(root->fs_info); + + /* + * Acquires fs_info->delete_unused_bgs_mutex to avoid racing + * with relocation (btrfs_relocate_chunk) and relocation + * acquires fs_info->cleaner_mutex (btrfs_relocate_block_group) + * after acquiring fs_info->delete_unused_bgs_mutex. So we + * can't hold, nor need to, fs_info->cleaner_mutex when deleting + * unused block groups. + */ + btrfs_delete_unused_bgs(root->fs_info); sleep: if (!try_to_freeze() && !again) { set_current_state(TASK_INTERRUPTIBLE); @@ -2492,6 +2501,7 @@ int open_ctree(struct super_block *sb, spin_lock_init(&fs_info->unused_bgs_lock); rwlock_init(&fs_info->tree_mod_log_lock); mutex_init(&fs_info->unused_bg_unpin_mutex); + mutex_init(&fs_info->delete_unused_bgs_mutex); mutex_init(&fs_info->reloc_mutex); mutex_init(&fs_info->delalloc_root_mutex); seqlock_init(&fs_info->profiles_lock); diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 38b76cc02f48..1c2bd1723e40 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -9889,6 +9889,8 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info) } spin_unlock(&fs_info->unused_bgs_lock); + mutex_lock(&root->fs_info->delete_unused_bgs_mutex); + /* Don't want to race with allocators so take the groups_sem */ down_write(&space_info->groups_sem); spin_lock(&block_group->lock); @@ -9983,6 +9985,7 @@ void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info) end_trans: btrfs_end_transaction(trans, root); next: + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); btrfs_put_block_group(block_group); spin_lock(&fs_info->unused_bgs_lock); } diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index d4cd4059bded..9b95503ddd00 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -2766,6 +2766,20 @@ static int btrfs_relocate_chunk(struct btrfs_root *root, root = root->fs_info->chunk_root; extent_root = root->fs_info->extent_root; + /* + * Prevent races with automatic removal of unused block groups. + * After we relocate and before we remove the chunk with offset + * chunk_offset, automatic removal of the block group can kick in, + * resulting in a failure when calling btrfs_remove_chunk() below. + * + * Make sure to acquire this mutex before doing a tree search (dev + * or chunk trees) to find chunks. Otherwise the cleaner kthread might + * call btrfs_remove_chunk() (through btrfs_delete_unused_bgs()) after + * we release the path used to search the chunk/dev tree and before + * the current task acquires this mutex and calls us. + */ + ASSERT(mutex_is_locked(&root->fs_info->delete_unused_bgs_mutex)); + ret = btrfs_can_relocate(extent_root, chunk_offset); if (ret) return -ENOSPC; @@ -2814,13 +2828,18 @@ again: key.type = BTRFS_CHUNK_ITEM_KEY; while (1) { + mutex_lock(&root->fs_info->delete_unused_bgs_mutex); ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0); - if (ret < 0) + if (ret < 0) { + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); goto error; + } BUG_ON(ret == 0); /* Corruption */ ret = btrfs_previous_item(chunk_root, path, key.objectid, key.type); + if (ret) + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); if (ret < 0) goto error; if (ret > 0) @@ -2843,6 +2862,7 @@ again: else BUG_ON(ret); } + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); if (found_key.offset == 0) break; @@ -3299,9 +3319,12 @@ again: goto error; } + mutex_lock(&fs_info->delete_unused_bgs_mutex); ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0); - if (ret < 0) + if (ret < 0) { + mutex_unlock(&fs_info->delete_unused_bgs_mutex); goto error; + } /* * this shouldn't happen, it means the last relocate @@ -3313,6 +3336,7 @@ again: ret = btrfs_previous_item(chunk_root, path, 0, BTRFS_CHUNK_ITEM_KEY); if (ret) { + mutex_unlock(&fs_info->delete_unused_bgs_mutex); ret = 0; break; } @@ -3321,8 +3345,10 @@ again: slot = path->slots[0]; btrfs_item_key_to_cpu(leaf, &found_key, slot); - if (found_key.objectid != key.objectid) + if (found_key.objectid != key.objectid) { + mutex_unlock(&fs_info->delete_unused_bgs_mutex); break; + } chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk); @@ -3335,10 +3361,13 @@ again: ret = should_balance_chunk(chunk_root, leaf, chunk, found_key.offset); btrfs_release_path(path); - if (!ret) + if (!ret) { + mutex_unlock(&fs_info->delete_unused_bgs_mutex); goto loop; + } if (counting) { + mutex_unlock(&fs_info->delete_unused_bgs_mutex); spin_lock(&fs_info->balance_lock); bctl->stat.expected++; spin_unlock(&fs_info->balance_lock); @@ -3348,6 +3377,7 @@ again: ret = btrfs_relocate_chunk(chunk_root, found_key.objectid, found_key.offset); + mutex_unlock(&fs_info->delete_unused_bgs_mutex); if (ret && ret != -ENOSPC) goto error; if (ret == -ENOSPC) { @@ -4087,11 +4117,16 @@ again: key.type = BTRFS_DEV_EXTENT_KEY; do { + mutex_lock(&root->fs_info->delete_unused_bgs_mutex); ret = btrfs_search_slot(NULL, root, &key, path, 0, 0); - if (ret < 0) + if (ret < 0) { + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); goto done; + } ret = btrfs_previous_item(root, path, 0, key.type); + if (ret) + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); if (ret < 0) goto done; if (ret) { @@ -4105,6 +4140,7 @@ again: btrfs_item_key_to_cpu(l, &key, path->slots[0]); if (key.objectid != device->devid) { + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); btrfs_release_path(path); break; } @@ -4113,6 +4149,7 @@ again: length = btrfs_dev_extent_length(l, dev_extent); if (key.offset + length <= new_size) { + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); btrfs_release_path(path); break; } @@ -4122,6 +4159,7 @@ again: btrfs_release_path(path); ret = btrfs_relocate_chunk(root, chunk_objectid, chunk_offset); + mutex_unlock(&root->fs_info->delete_unused_bgs_mutex); if (ret && ret != -ENOSPC) goto done; if (ret == -ENOSPC)