From d2c609b834d62f1e91f1635a27dca29f7806d3d6 Mon Sep 17 00:00:00 2001 From: Jeff Mahoney Date: Mon, 15 Aug 2016 12:10:33 -0400 Subject: btrfs: properly track when rescan worker is running The qgroup_flags field is overloaded such that it reflects the on-disk status of qgroups and the runtime state. The BTRFS_QGROUP_STATUS_FLAG_RESCAN flag is used to indicate that a rescan operation is in progress, but if the file system is unmounted while a rescan is running, the rescan operation is paused. If the file system is then mounted read-only, the flag will still be present but the rescan operation will not have been resumed. When we go to umount, btrfs_qgroup_wait_for_completion will see the flag and interpret it to mean that the rescan worker is still running and will wait for a completion that will never come. This patch uses a separate flag to indicate when the worker is running. The locking and state surrounding the qgroup rescan worker needs a lot of attention beyond this patch but this is enough to avoid a hung umount. Cc: # v4.4+ Signed-off-by; Jeff Mahoney Reviewed-by: Qu Wenruo Signed-off-by: David Sterba Signed-off-by: Chris Mason --- fs/btrfs/ctree.h | 1 + 1 file changed, 1 insertion(+) (limited to 'fs/btrfs/ctree.h') diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index f66a0ba9a2a9..acc6850a118f 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -1028,6 +1028,7 @@ struct btrfs_fs_info { struct btrfs_workqueue *qgroup_rescan_workers; struct completion qgroup_rescan_completion; struct btrfs_work qgroup_rescan_work; + bool qgroup_rescan_running; /* protected by qgroup_rescan_lock */ /* filesystem state */ unsigned long fs_state; -- cgit v1.2.2 From 18513091af9483ba84328d42092bd4d42a3c958f Mon Sep 17 00:00:00 2001 From: Wang Xiaoguang Date: Mon, 25 Jul 2016 15:51:40 +0800 Subject: btrfs: update btrfs_space_info's bytes_may_use timely This patch can fix some false ENOSPC errors, below test script can reproduce one false ENOSPC error: #!/bin/bash dd if=/dev/zero of=fs.img bs=$((1024*1024)) count=128 dev=$(losetup --show -f fs.img) mkfs.btrfs -f -M $dev mkdir /tmp/mntpoint mount $dev /tmp/mntpoint cd /tmp/mntpoint xfs_io -f -c "falloc 0 $((64*1024*1024))" testfile Above script will fail for ENOSPC reason, but indeed fs still has free space to satisfy this request. Please see call graph: btrfs_fallocate() |-> btrfs_alloc_data_chunk_ondemand() | bytes_may_use += 64M |-> btrfs_prealloc_file_range() |-> btrfs_reserve_extent() |-> btrfs_add_reserved_bytes() | alloc_type is RESERVE_ALLOC_NO_ACCOUNT, so it does not | change bytes_may_use, and bytes_reserved += 64M. Now | bytes_may_use + bytes_reserved == 128M, which is greater | than btrfs_space_info's total_bytes, false enospc occurs. | Note, the bytes_may_use decrease operation will be done in | end of btrfs_fallocate(), which is too late. Here is another simple case for buffered write: CPU 1 | CPU 2 | |-> cow_file_range() |-> __btrfs_buffered_write() |-> btrfs_reserve_extent() | | | | | | | | | ..... | |-> btrfs_check_data_free_space() | | | | |-> extent_clear_unlock_delalloc() | In CPU 1, btrfs_reserve_extent()->find_free_extent()-> btrfs_add_reserved_bytes() do not decrease bytes_may_use, the decrease operation will be delayed to be done in extent_clear_unlock_delalloc(). Assume in this case, btrfs_reserve_extent() reserved 128MB data, CPU2's btrfs_check_data_free_space() tries to reserve 100MB data space. If 100MB > data_sinfo->total_bytes - data_sinfo->bytes_used - data_sinfo->bytes_reserved - data_sinfo->bytes_pinned - data_sinfo->bytes_readonly - data_sinfo->bytes_may_use btrfs_check_data_free_space() will try to allcate new data chunk or call btrfs_start_delalloc_roots(), or commit current transaction in order to reserve some free space, obviously a lot of work. But indeed it's not necessary as long as decreasing bytes_may_use timely, we still have free space, decreasing 128M from bytes_may_use. To fix this issue, this patch chooses to update bytes_may_use for both data and metadata in btrfs_add_reserved_bytes(). For compress path, real extent length may not be equal to file content length, so introduce a ram_bytes argument for btrfs_reserve_extent(), find_free_extent() and btrfs_add_reserved_bytes(), it's becasue bytes_may_use is increased by file content length. Then compress path can update bytes_may_use correctly. Also now we can discard RESERVE_ALLOC_NO_ACCOUNT, RESERVE_ALLOC and RESERVE_FREE. As we know, usually EXTENT_DO_ACCOUNTING is used for error path. In run_delalloc_nocow(), for inode marked as NODATACOW or extent marked as PREALLOC, we also need to update bytes_may_use, but can not pass EXTENT_DO_ACCOUNTING, because it also clears metadata reservation, so here we introduce EXTENT_CLEAR_DATA_RESV flag to indicate btrfs_clear_bit_hook() to update btrfs_space_info's bytes_may_use. Meanwhile __btrfs_prealloc_file_range() will call btrfs_free_reserved_data_space() internally for both sucessful and failed path, btrfs_prealloc_file_range()'s callers does not need to call btrfs_free_reserved_data_space() any more. Signed-off-by: Wang Xiaoguang Reviewed-by: Josef Bacik Signed-off-by: David Sterba Signed-off-by: Chris Mason --- fs/btrfs/ctree.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/btrfs/ctree.h') diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index acc6850a118f..09cdff0d58e8 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -2579,7 +2579,7 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans, struct btrfs_root *root, u64 root_objectid, u64 owner, u64 offset, struct btrfs_key *ins); -int btrfs_reserve_extent(struct btrfs_root *root, u64 num_bytes, +int btrfs_reserve_extent(struct btrfs_root *root, u64 ram_bytes, u64 num_bytes, u64 min_alloc_size, u64 empty_size, u64 hint_byte, struct btrfs_key *ins, int is_data, int delalloc); int btrfs_inc_ref(struct btrfs_trans_handle *trans, struct btrfs_root *root, -- cgit v1.2.2 From 9e7cc91a6d18a4973c6d2cc104871439c9e94f3d Mon Sep 17 00:00:00 2001 From: Wang Xiaoguang Date: Mon, 1 Aug 2016 13:28:08 +0800 Subject: btrfs: fix fsfreeze hang caused by delayed iputs deal When running fstests generic/068, sometimes we got below deadlock: xfs_io D ffff8800331dbb20 0 6697 6693 0x00000080 ffff8800331dbb20 ffff88007acfc140 ffff880034d895c0 ffff8800331dc000 ffff880032d243e8 fffffffeffffffff ffff880032d24400 0000000000000001 ffff8800331dbb38 ffffffff816a9045 ffff880034d895c0 ffff8800331dbba8 Call Trace: [] schedule+0x35/0x80 [] rwsem_down_read_failed+0xf2/0x140 [] ? __filemap_fdatawrite_range+0xd1/0x100 [] call_rwsem_down_read_failed+0x18/0x30 [] ? btrfs_alloc_block_rsv+0x2c/0xb0 [btrfs] [] percpu_down_read+0x35/0x50 [] __sb_start_write+0x2c/0x40 [] start_transaction+0x2a5/0x4d0 [btrfs] [] btrfs_join_transaction+0x17/0x20 [btrfs] [] btrfs_evict_inode+0x3c4/0x5d0 [btrfs] [] evict+0xba/0x1a0 [] iput+0x196/0x200 [] btrfs_run_delayed_iputs+0x70/0xc0 [btrfs] [] btrfs_commit_transaction+0x928/0xa80 [btrfs] [] btrfs_freeze+0x30/0x40 [btrfs] [] freeze_super+0xf0/0x190 [] do_vfs_ioctl+0x4a5/0x5c0 [] ? do_audit_syscall_entry+0x66/0x70 [] ? syscall_trace_enter_phase1+0x11f/0x140 [] SyS_ioctl+0x79/0x90 [] do_syscall_64+0x62/0x110 [] entry_SYSCALL64_slow_path+0x25/0x25 >From this warning, freeze_super() already holds SB_FREEZE_FS, but btrfs_freeze() will call btrfs_commit_transaction() again, if btrfs_commit_transaction() finds that it has delayed iputs to handle, it'll start_transaction(), which will try to get SB_FREEZE_FS lock again, then deadlock occurs. The root cause is that in btrfs, sync_filesystem(sb) does not make sure all metadata is updated. There still maybe some codes adding delayed iputs, see below sample race window: CPU1 | CPU2 |-> freeze_super() | |-> sync_filesystem(sb); | | |-> cleaner_kthread() | | |-> btrfs_delete_unused_bgs() | | |-> btrfs_remove_chunk() | | |-> btrfs_remove_block_group() | | |-> btrfs_add_delayed_iput() | | |-> sb->s_writers.frozen = SB_FREEZE_FS; | |-> sb_wait_write(sb, SB_FREEZE_FS); | | acquire SB_FREEZE_FS lock. | | | |-> btrfs_freeze() | |-> btrfs_commit_transaction() | |-> btrfs_run_delayed_iputs() | | will handle delayed iputs, | | that means start_transaction() | | will be called, which will try | | to get SB_FREEZE_FS lock. | To fix this issue, introduce a "int fs_frozen" to record internally whether fs has been frozen. If fs has been frozen, we can not handle delayed iputs. Signed-off-by: Wang Xiaoguang Reviewed-by: David Sterba [ add comment to btrfs_freeze ] Signed-off-by: David Sterba Signed-off-by: Chris Mason --- fs/btrfs/ctree.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'fs/btrfs/ctree.h') diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h index 09cdff0d58e8..ec4154faab61 100644 --- a/fs/btrfs/ctree.h +++ b/fs/btrfs/ctree.h @@ -1080,6 +1080,8 @@ struct btrfs_fs_info { struct list_head pinned_chunks; int creating_free_space_tree; + /* Used to record internally whether fs has been frozen */ + int fs_frozen; }; struct btrfs_subvolume_writers { -- cgit v1.2.2