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![Filipe Manana](/assets/img/avatar_default.png)
When a task is doing some modification to the chunk btree and it is not in
the context of a chunk allocation or a chunk removal, it can deadlock with
another task that is currently allocating a new data or metadata chunk.
These contexts are the following:
* When relocating a system chunk, when we need to COW the extent buffers
that belong to the chunk btree;
* When adding a new device (ioctl), where we need to add a new device item
to the chunk btree;
* When removing a device (ioctl), where we need to remove a device item
from the chunk btree;
* When resizing a device (ioctl), where we need to update a device item in
the chunk btree and may need to relocate a system chunk that lies beyond
the new device size when shrinking a device.
The problem happens due to a sequence of steps like the following:
1) Task A starts a data or metadata chunk allocation and it locks the
chunk mutex;
2) Task B is relocating a system chunk, and when it needs to COW an extent
buffer of the chunk btree, it has locked both that extent buffer as
well as its parent extent buffer;
3) Since there is not enough available system space, either because none
of the existing system block groups have enough free space or because
the only one with enough free space is in RO mode due to the relocation,
task B triggers a new system chunk allocation. It blocks when trying to
acquire the chunk mutex, currently held by task A;
4) Task A enters btrfs_chunk_alloc_add_chunk_item(), in order to insert
the new chunk item into the chunk btree and update the existing device
items there. But in order to do that, it has to lock the extent buffer
that task B locked at step 2, or its parent extent buffer, but task B
is waiting on the chunk mutex, which is currently locked by task A,
therefore resulting in a deadlock.
One example report when the deadlock happens with system chunk relocation:
INFO: task kworker/u9:5:546 blocked for more than 143 seconds.
Not tainted 5.15.0-rc3+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u9:5 state:D stack:25936 pid: 546 ppid: 2 flags:0x00004000
Workqueue: events_unbound btrfs_async_reclaim_metadata_space
Call Trace:
context_switch kernel/sched/core.c:4940 [inline]
__schedule+0xcd9/0x2530 kernel/sched/core.c:6287
schedule+0xd3/0x270 kernel/sched/core.c:6366
rwsem_down_read_slowpath+0x4ee/0x9d0 kernel/locking/rwsem.c:993
__down_read_common kernel/locking/rwsem.c:1214 [inline]
__down_read kernel/locking/rwsem.c:1223 [inline]
down_read_nested+0xe6/0x440 kernel/locking/rwsem.c:1590
__btrfs_tree_read_lock+0x31/0x350 fs/btrfs/locking.c:47
btrfs_tree_read_lock fs/btrfs/locking.c:54 [inline]
btrfs_read_lock_root_node+0x8a/0x320 fs/btrfs/locking.c:191
btrfs_search_slot_get_root fs/btrfs/ctree.c:1623 [inline]
btrfs_search_slot+0x13b4/0x2140 fs/btrfs/ctree.c:1728
btrfs_update_device+0x11f/0x500 fs/btrfs/volumes.c:2794
btrfs_chunk_alloc_add_chunk_item+0x34d/0xea0 fs/btrfs/volumes.c:5504
do_chunk_alloc fs/btrfs/block-group.c:3408 [inline]
btrfs_chunk_alloc+0x84d/0xf50 fs/btrfs/block-group.c:3653
flush_space+0x54e/0xd80 fs/btrfs/space-info.c:670
btrfs_async_reclaim_metadata_space+0x396/0xa90 fs/btrfs/space-info.c:953
process_one_work+0x9df/0x16d0 kernel/workqueue.c:2297
worker_thread+0x90/0xed0 kernel/workqueue.c:2444
kthread+0x3e5/0x4d0 kernel/kthread.c:319
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
INFO: task syz-executor:9107 blocked for more than 143 seconds.
Not tainted 5.15.0-rc3+ #1
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor state:D stack:23200 pid: 9107 ppid: 7792 flags:0x00004004
Call Trace:
context_switch kernel/sched/core.c:4940 [inline]
__schedule+0xcd9/0x2530 kernel/sched/core.c:6287
schedule+0xd3/0x270 kernel/sched/core.c:6366
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6425
__mutex_lock_common kernel/locking/mutex.c:669 [inline]
__mutex_lock+0xc96/0x1680 kernel/locking/mutex.c:729
btrfs_chunk_alloc+0x31a/0xf50 fs/btrfs/block-group.c:3631
find_free_extent_update_loop fs/btrfs/extent-tree.c:3986 [inline]
find_free_extent+0x25cb/0x3a30 fs/btrfs/extent-tree.c:4335
btrfs_reserve_extent+0x1f1/0x500 fs/btrfs/extent-tree.c:4415
btrfs_alloc_tree_block+0x203/0x1120 fs/btrfs/extent-tree.c:4813
__btrfs_cow_block+0x412/0x1620 fs/btrfs/ctree.c:415
btrfs_cow_block+0x2f6/0x8c0 fs/btrfs/ctree.c:570
btrfs_search_slot+0x1094/0x2140 fs/btrfs/ctree.c:1768
relocate_tree_block fs/btrfs/relocation.c:2694 [inline]
relocate_tree_blocks+0xf73/0x1770 fs/btrfs/relocation.c:2757
relocate_block_group+0x47e/0xc70 fs/btrfs/relocation.c:3673
btrfs_relocate_block_group+0x48a/0xc60 fs/btrfs/relocation.c:4070
btrfs_relocate_chunk+0x96/0x280 fs/btrfs/volumes.c:3181
__btrfs_balance fs/btrfs/volumes.c:3911 [inline]
btrfs_balance+0x1f03/0x3cd0 fs/btrfs/volumes.c:4301
btrfs_ioctl_balance+0x61e/0x800 fs/btrfs/ioctl.c:4137
btrfs_ioctl+0x39ea/0x7b70 fs/btrfs/ioctl.c:4949
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl fs/ioctl.c:860 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
So fix this by making sure that whenever we try to modify the chunk btree
and we are neither in a chunk allocation context nor in a chunk remove
context, we reserve system space before modifying the chunk btree.
Reported-by: Hao Sun <sunhao.th@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CACkBjsax51i4mu6C0C3vJqQN3NR_iVuucoeG3U1HXjrgzn5FFQ@mail.gmail.com/
Fixes: 79bd37120b
("btrfs: rework chunk allocation to avoid exhaustion of the system chunk array")
CC: stable@vger.kernel.org # 5.14+
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
335 lines
11 KiB
C
335 lines
11 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef BTRFS_BLOCK_GROUP_H
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#define BTRFS_BLOCK_GROUP_H
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#include "free-space-cache.h"
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enum btrfs_disk_cache_state {
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BTRFS_DC_WRITTEN,
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BTRFS_DC_ERROR,
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BTRFS_DC_CLEAR,
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BTRFS_DC_SETUP,
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};
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/*
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* This describes the state of the block_group for async discard. This is due
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* to the two pass nature of it where extent discarding is prioritized over
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* bitmap discarding. BTRFS_DISCARD_RESET_CURSOR is set when we are resetting
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* between lists to prevent contention for discard state variables
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* (eg. discard_cursor).
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*/
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enum btrfs_discard_state {
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BTRFS_DISCARD_EXTENTS,
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BTRFS_DISCARD_BITMAPS,
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BTRFS_DISCARD_RESET_CURSOR,
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};
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/*
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* Control flags for do_chunk_alloc's force field CHUNK_ALLOC_NO_FORCE means to
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* only allocate a chunk if we really need one.
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*
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* CHUNK_ALLOC_LIMITED means to only try and allocate one if we have very few
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* chunks already allocated. This is used as part of the clustering code to
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* help make sure we have a good pool of storage to cluster in, without filling
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* the FS with empty chunks
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*
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* CHUNK_ALLOC_FORCE means it must try to allocate one
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*/
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enum btrfs_chunk_alloc_enum {
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CHUNK_ALLOC_NO_FORCE,
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CHUNK_ALLOC_LIMITED,
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CHUNK_ALLOC_FORCE,
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};
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struct btrfs_caching_control {
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struct list_head list;
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struct mutex mutex;
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wait_queue_head_t wait;
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struct btrfs_work work;
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struct btrfs_block_group *block_group;
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u64 progress;
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refcount_t count;
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};
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/* Once caching_thread() finds this much free space, it will wake up waiters. */
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#define CACHING_CTL_WAKE_UP SZ_2M
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struct btrfs_block_group {
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struct btrfs_fs_info *fs_info;
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struct inode *inode;
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spinlock_t lock;
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u64 start;
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u64 length;
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u64 pinned;
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u64 reserved;
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u64 used;
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u64 delalloc_bytes;
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u64 bytes_super;
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u64 flags;
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u64 cache_generation;
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/*
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* If the free space extent count exceeds this number, convert the block
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* group to bitmaps.
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*/
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u32 bitmap_high_thresh;
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/*
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* If the free space extent count drops below this number, convert the
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* block group back to extents.
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*/
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u32 bitmap_low_thresh;
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/*
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* It is just used for the delayed data space allocation because
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* only the data space allocation and the relative metadata update
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* can be done cross the transaction.
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*/
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struct rw_semaphore data_rwsem;
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/* For raid56, this is a full stripe, without parity */
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unsigned long full_stripe_len;
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unsigned int ro;
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unsigned int iref:1;
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unsigned int has_caching_ctl:1;
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unsigned int removed:1;
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unsigned int to_copy:1;
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unsigned int relocating_repair:1;
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unsigned int chunk_item_inserted:1;
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unsigned int zone_is_active:1;
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int disk_cache_state;
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/* Cache tracking stuff */
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int cached;
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struct btrfs_caching_control *caching_ctl;
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u64 last_byte_to_unpin;
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struct btrfs_space_info *space_info;
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/* Free space cache stuff */
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struct btrfs_free_space_ctl *free_space_ctl;
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/* Block group cache stuff */
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struct rb_node cache_node;
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/* For block groups in the same raid type */
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struct list_head list;
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refcount_t refs;
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/*
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* List of struct btrfs_free_clusters for this block group.
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* Today it will only have one thing on it, but that may change
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*/
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struct list_head cluster_list;
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/* For delayed block group creation or deletion of empty block groups */
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struct list_head bg_list;
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/* For read-only block groups */
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struct list_head ro_list;
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/*
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* When non-zero it means the block group's logical address and its
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* device extents can not be reused for future block group allocations
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* until the counter goes down to 0. This is to prevent them from being
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* reused while some task is still using the block group after it was
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* deleted - we want to make sure they can only be reused for new block
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* groups after that task is done with the deleted block group.
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*/
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atomic_t frozen;
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/* For discard operations */
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struct list_head discard_list;
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int discard_index;
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u64 discard_eligible_time;
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u64 discard_cursor;
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enum btrfs_discard_state discard_state;
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/* For dirty block groups */
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struct list_head dirty_list;
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struct list_head io_list;
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struct btrfs_io_ctl io_ctl;
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/*
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* Incremented when doing extent allocations and holding a read lock
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* on the space_info's groups_sem semaphore.
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* Decremented when an ordered extent that represents an IO against this
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* block group's range is created (after it's added to its inode's
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* root's list of ordered extents) or immediately after the allocation
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* if it's a metadata extent or fallocate extent (for these cases we
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* don't create ordered extents).
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*/
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atomic_t reservations;
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/*
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* Incremented while holding the spinlock *lock* by a task checking if
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* it can perform a nocow write (incremented if the value for the *ro*
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* field is 0). Decremented by such tasks once they create an ordered
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* extent or before that if some error happens before reaching that step.
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* This is to prevent races between block group relocation and nocow
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* writes through direct IO.
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*/
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atomic_t nocow_writers;
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/* Lock for free space tree operations. */
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struct mutex free_space_lock;
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/*
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* Does the block group need to be added to the free space tree?
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* Protected by free_space_lock.
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*/
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int needs_free_space;
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/* Flag indicating this block group is placed on a sequential zone */
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bool seq_zone;
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/*
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* Number of extents in this block group used for swap files.
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* All accesses protected by the spinlock 'lock'.
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*/
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int swap_extents;
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/* Record locked full stripes for RAID5/6 block group */
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struct btrfs_full_stripe_locks_tree full_stripe_locks_root;
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/*
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* Allocation offset for the block group to implement sequential
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* allocation. This is used only on a zoned filesystem.
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*/
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u64 alloc_offset;
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u64 zone_unusable;
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u64 zone_capacity;
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u64 meta_write_pointer;
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struct map_lookup *physical_map;
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struct list_head active_bg_list;
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};
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static inline u64 btrfs_block_group_end(struct btrfs_block_group *block_group)
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{
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return (block_group->start + block_group->length);
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}
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static inline bool btrfs_is_block_group_data_only(
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struct btrfs_block_group *block_group)
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{
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/*
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* In mixed mode the fragmentation is expected to be high, lowering the
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* efficiency, so only proper data block groups are considered.
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*/
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return (block_group->flags & BTRFS_BLOCK_GROUP_DATA) &&
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!(block_group->flags & BTRFS_BLOCK_GROUP_METADATA);
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}
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#ifdef CONFIG_BTRFS_DEBUG
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static inline int btrfs_should_fragment_free_space(
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struct btrfs_block_group *block_group)
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{
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struct btrfs_fs_info *fs_info = block_group->fs_info;
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return (btrfs_test_opt(fs_info, FRAGMENT_METADATA) &&
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block_group->flags & BTRFS_BLOCK_GROUP_METADATA) ||
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(btrfs_test_opt(fs_info, FRAGMENT_DATA) &&
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block_group->flags & BTRFS_BLOCK_GROUP_DATA);
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}
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#endif
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struct btrfs_block_group *btrfs_lookup_first_block_group(
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struct btrfs_fs_info *info, u64 bytenr);
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struct btrfs_block_group *btrfs_lookup_block_group(
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struct btrfs_fs_info *info, u64 bytenr);
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struct btrfs_block_group *btrfs_next_block_group(
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struct btrfs_block_group *cache);
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void btrfs_get_block_group(struct btrfs_block_group *cache);
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void btrfs_put_block_group(struct btrfs_block_group *cache);
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void btrfs_dec_block_group_reservations(struct btrfs_fs_info *fs_info,
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const u64 start);
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void btrfs_wait_block_group_reservations(struct btrfs_block_group *bg);
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bool btrfs_inc_nocow_writers(struct btrfs_fs_info *fs_info, u64 bytenr);
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void btrfs_dec_nocow_writers(struct btrfs_fs_info *fs_info, u64 bytenr);
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void btrfs_wait_nocow_writers(struct btrfs_block_group *bg);
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void btrfs_wait_block_group_cache_progress(struct btrfs_block_group *cache,
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u64 num_bytes);
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int btrfs_wait_block_group_cache_done(struct btrfs_block_group *cache);
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int btrfs_cache_block_group(struct btrfs_block_group *cache,
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int load_cache_only);
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void btrfs_put_caching_control(struct btrfs_caching_control *ctl);
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struct btrfs_caching_control *btrfs_get_caching_control(
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struct btrfs_block_group *cache);
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u64 add_new_free_space(struct btrfs_block_group *block_group,
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u64 start, u64 end);
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struct btrfs_trans_handle *btrfs_start_trans_remove_block_group(
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struct btrfs_fs_info *fs_info,
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const u64 chunk_offset);
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int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
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u64 group_start, struct extent_map *em);
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void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info);
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void btrfs_mark_bg_unused(struct btrfs_block_group *bg);
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void btrfs_reclaim_bgs_work(struct work_struct *work);
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void btrfs_reclaim_bgs(struct btrfs_fs_info *fs_info);
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void btrfs_mark_bg_to_reclaim(struct btrfs_block_group *bg);
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int btrfs_read_block_groups(struct btrfs_fs_info *info);
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struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *trans,
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u64 bytes_used, u64 type,
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u64 chunk_offset, u64 size);
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void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans);
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int btrfs_inc_block_group_ro(struct btrfs_block_group *cache,
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bool do_chunk_alloc);
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void btrfs_dec_block_group_ro(struct btrfs_block_group *cache);
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int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans);
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int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans);
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int btrfs_setup_space_cache(struct btrfs_trans_handle *trans);
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int btrfs_update_block_group(struct btrfs_trans_handle *trans,
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u64 bytenr, u64 num_bytes, bool alloc);
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int btrfs_add_reserved_bytes(struct btrfs_block_group *cache,
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u64 ram_bytes, u64 num_bytes, int delalloc);
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void btrfs_free_reserved_bytes(struct btrfs_block_group *cache,
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u64 num_bytes, int delalloc);
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int btrfs_chunk_alloc(struct btrfs_trans_handle *trans, u64 flags,
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enum btrfs_chunk_alloc_enum force);
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int btrfs_force_chunk_alloc(struct btrfs_trans_handle *trans, u64 type);
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void check_system_chunk(struct btrfs_trans_handle *trans, const u64 type);
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void btrfs_reserve_chunk_metadata(struct btrfs_trans_handle *trans,
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bool is_item_insertion);
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u64 btrfs_get_alloc_profile(struct btrfs_fs_info *fs_info, u64 orig_flags);
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void btrfs_put_block_group_cache(struct btrfs_fs_info *info);
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int btrfs_free_block_groups(struct btrfs_fs_info *info);
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void btrfs_wait_space_cache_v1_finished(struct btrfs_block_group *cache,
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struct btrfs_caching_control *caching_ctl);
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int btrfs_rmap_block(struct btrfs_fs_info *fs_info, u64 chunk_start,
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struct block_device *bdev, u64 physical, u64 **logical,
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int *naddrs, int *stripe_len);
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static inline u64 btrfs_data_alloc_profile(struct btrfs_fs_info *fs_info)
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{
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return btrfs_get_alloc_profile(fs_info, BTRFS_BLOCK_GROUP_DATA);
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}
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static inline u64 btrfs_metadata_alloc_profile(struct btrfs_fs_info *fs_info)
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{
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return btrfs_get_alloc_profile(fs_info, BTRFS_BLOCK_GROUP_METADATA);
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}
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static inline u64 btrfs_system_alloc_profile(struct btrfs_fs_info *fs_info)
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{
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return btrfs_get_alloc_profile(fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
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}
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static inline int btrfs_block_group_done(struct btrfs_block_group *cache)
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{
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|
smp_mb();
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return cache->cached == BTRFS_CACHE_FINISHED ||
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cache->cached == BTRFS_CACHE_ERROR;
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}
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|
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void btrfs_freeze_block_group(struct btrfs_block_group *cache);
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void btrfs_unfreeze_block_group(struct btrfs_block_group *cache);
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|
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bool btrfs_inc_block_group_swap_extents(struct btrfs_block_group *bg);
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void btrfs_dec_block_group_swap_extents(struct btrfs_block_group *bg, int amount);
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|
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#endif /* BTRFS_BLOCK_GROUP_H */
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