![Filipe Manana](/assets/img/avatar_default.png)
Trimming is completely transactionless, and the way it operates consists of hiding free space entries from a block group, perform the trim/discard and then make the free space entries visible again. Therefore while a free space entry is being trimmed, we can have free space cache writing running in parallel (as part of a transaction commit) which will miss the free space entry. This means that an unmount (or crash/reboot) after that transaction commit and mount again before another transaction starts/commits after the discard finishes, we will have some free space that won't be used again unless the free space cache is rebuilt. After the unmount, fsck (btrfsck, btrfs check) reports the issue like the following example: *** fsck.btrfs output *** checking extents checking free space cache There is no free space entry for 521764864-521781248 There is no free space entry for 521764864-1103101952 cache appears valid but isnt 29360128 Checking filesystem on /dev/sdc UUID: b4789e27-4774-4626-98e9-ae8dfbfb0fb5 found 1235681286 bytes used err is -22 (...) Another issue caused by this race is a crash while writing bitmap entries to the cache, because while the cache writeout task accesses the bitmaps, the trim task can be concurrently modifying the bitmap or worse might be freeing the bitmap. The later case results in the following crash: [55650.804460] general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC [55650.804835] Modules linked in: btrfs dm_flakey dm_mod crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd fscache sunrpc loop parport_pc parport i2c_piix4 psmouse evdev pcspkr microcode processor i2ccore serio_raw thermal_sys button ext4 crc16 jbd2 mbcache sg sd_mod crc_t10dif sr_mod cdrom crct10dif_generic crct10dif_common ata_generic virtio_scsi floppy ata_piix libata virtio_pci virtio_ring virtio scsi_mod e1000 [last unloaded: btrfs] [55650.806169] CPU: 1 PID: 31002 Comm: btrfs-transacti Tainted: G W 3.17.0-rc5-btrfs-next-1+ #1 [55650.806493] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014 [55650.806867] task: ffff8800b12f6410 ti: ffff880071538000 task.ti: ffff880071538000 [55650.807166] RIP: 0010:[<ffffffffa037cf45>] [<ffffffffa037cf45>] write_bitmap_entries+0x65/0xbb [btrfs] [55650.807514] RSP: 0018:ffff88007153bc30 EFLAGS: 00010246 [55650.807687] RAX: 000000005d1ec000 RBX: ffff8800a665df08 RCX: 0000000000000400 [55650.807885] RDX: ffff88005d1ec000 RSI: 6b6b6b6b6b6b6b6b RDI: ffff88005d1ec000 [55650.808017] RBP: ffff88007153bc58 R08: 00000000ddd51536 R09: 00000000000001e0 [55650.808017] R10: 0000000000000000 R11: 0000000000000037 R12: 6b6b6b6b6b6b6b6b [55650.808017] R13: ffff88007153bca8 R14: 6b6b6b6b6b6b6b6b R15: ffff88007153bc98 [55650.808017] FS: 0000000000000000(0000) GS:ffff88023ec80000(0000) knlGS:0000000000000000 [55650.808017] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [55650.808017] CR2: 0000000002273b88 CR3: 00000000b18f6000 CR4: 00000000000006e0 [55650.808017] Stack: [55650.808017] ffff88020e834e00 ffff880172d68db0 0000000000000000 ffff88019257c800 [55650.808017] ffff8801d42ea720 ffff88007153bd10 ffffffffa037d2fa ffff880224e99180 [55650.808017] ffff8801469a6188 ffff880224e99140 ffff880172d68c50 00000003000000b7 [55650.808017] Call Trace: [55650.808017] [<ffffffffa037d2fa>] __btrfs_write_out_cache+0x1ea/0x37f [btrfs] [55650.808017] [<ffffffffa037d959>] btrfs_write_out_cache+0xa1/0xd8 [btrfs] [55650.808017] [<ffffffffa033936b>] btrfs_write_dirty_block_groups+0x4b5/0x505 [btrfs] [55650.808017] [<ffffffffa03aa98e>] commit_cowonly_roots+0x15e/0x1f7 [btrfs] [55650.808017] [<ffffffff813eb9c7>] ? _raw_spin_lock+0xe/0x10 [55650.808017] [<ffffffffa0346e46>] btrfs_commit_transaction+0x411/0x882 [btrfs] [55650.808017] [<ffffffffa03432a4>] transaction_kthread+0xf2/0x1a4 [btrfs] [55650.808017] [<ffffffffa03431b2>] ? btrfs_cleanup_transaction+0x3d8/0x3d8 [btrfs] [55650.808017] [<ffffffff8105966b>] kthread+0xb7/0xbf [55650.808017] [<ffffffff810595b4>] ? __kthread_parkme+0x67/0x67 [55650.808017] [<ffffffff813ebeac>] ret_from_fork+0x7c/0xb0 [55650.808017] [<ffffffff810595b4>] ? __kthread_parkme+0x67/0x67 [55650.808017] Code: 4c 89 ef 8d 70 ff e8 d4 fc ff ff 41 8b 45 34 41 39 45 30 7d 5c 31 f6 4c 89 ef e8 80 f6 ff ff 49 8b 7d 00 4c 89 f6 b9 00 04 00 00 <f3> a5 4c 89 ef 41 8b 45 30 8d 70 ff e8 a3 fc ff ff 41 8b 45 34 [55650.808017] RIP [<ffffffffa037cf45>] write_bitmap_entries+0x65/0xbb [btrfs] [55650.808017] RSP <ffff88007153bc30> [55650.815725] ---[ end trace 1c032e96b149ff86 ]--- Fix this by serializing both tasks in such a way that cache writeout doesn't wait for the trim/discard of free space entries to finish and doesn't miss any free space entry. Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
127 lines
4.6 KiB
C
127 lines
4.6 KiB
C
/*
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* Copyright (C) 2009 Oracle. All rights reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public
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* License v2 as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public
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* License along with this program; if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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* Boston, MA 021110-1307, USA.
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*/
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#ifndef __BTRFS_FREE_SPACE_CACHE
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#define __BTRFS_FREE_SPACE_CACHE
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struct btrfs_free_space {
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struct rb_node offset_index;
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u64 offset;
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u64 bytes;
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unsigned long *bitmap;
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struct list_head list;
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};
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struct btrfs_free_space_ctl {
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spinlock_t tree_lock;
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struct rb_root free_space_offset;
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u64 free_space;
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int extents_thresh;
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int free_extents;
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int total_bitmaps;
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int unit;
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u64 start;
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struct btrfs_free_space_op *op;
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void *private;
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struct mutex cache_writeout_mutex;
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struct list_head trimming_ranges;
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};
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struct btrfs_free_space_op {
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void (*recalc_thresholds)(struct btrfs_free_space_ctl *ctl);
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bool (*use_bitmap)(struct btrfs_free_space_ctl *ctl,
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struct btrfs_free_space *info);
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};
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struct inode *lookup_free_space_inode(struct btrfs_root *root,
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struct btrfs_block_group_cache
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*block_group, struct btrfs_path *path);
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int create_free_space_inode(struct btrfs_root *root,
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struct btrfs_trans_handle *trans,
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struct btrfs_block_group_cache *block_group,
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struct btrfs_path *path);
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int btrfs_check_trunc_cache_free_space(struct btrfs_root *root,
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struct btrfs_block_rsv *rsv);
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int btrfs_truncate_free_space_cache(struct btrfs_root *root,
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struct btrfs_trans_handle *trans,
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struct inode *inode);
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int load_free_space_cache(struct btrfs_fs_info *fs_info,
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struct btrfs_block_group_cache *block_group);
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int btrfs_write_out_cache(struct btrfs_root *root,
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struct btrfs_trans_handle *trans,
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struct btrfs_block_group_cache *block_group,
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struct btrfs_path *path);
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struct inode *lookup_free_ino_inode(struct btrfs_root *root,
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struct btrfs_path *path);
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int create_free_ino_inode(struct btrfs_root *root,
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struct btrfs_trans_handle *trans,
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struct btrfs_path *path);
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int load_free_ino_cache(struct btrfs_fs_info *fs_info,
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struct btrfs_root *root);
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int btrfs_write_out_ino_cache(struct btrfs_root *root,
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struct btrfs_trans_handle *trans,
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struct btrfs_path *path,
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struct inode *inode);
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void btrfs_init_free_space_ctl(struct btrfs_block_group_cache *block_group);
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int __btrfs_add_free_space(struct btrfs_free_space_ctl *ctl,
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u64 bytenr, u64 size);
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static inline int
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btrfs_add_free_space(struct btrfs_block_group_cache *block_group,
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u64 bytenr, u64 size)
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{
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return __btrfs_add_free_space(block_group->free_space_ctl,
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bytenr, size);
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}
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int btrfs_remove_free_space(struct btrfs_block_group_cache *block_group,
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u64 bytenr, u64 size);
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void __btrfs_remove_free_space_cache(struct btrfs_free_space_ctl *ctl);
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void btrfs_remove_free_space_cache(struct btrfs_block_group_cache
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*block_group);
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u64 btrfs_find_space_for_alloc(struct btrfs_block_group_cache *block_group,
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u64 offset, u64 bytes, u64 empty_size,
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u64 *max_extent_size);
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u64 btrfs_find_ino_for_alloc(struct btrfs_root *fs_root);
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void btrfs_dump_free_space(struct btrfs_block_group_cache *block_group,
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u64 bytes);
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int btrfs_find_space_cluster(struct btrfs_root *root,
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struct btrfs_block_group_cache *block_group,
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struct btrfs_free_cluster *cluster,
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u64 offset, u64 bytes, u64 empty_size);
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void btrfs_init_free_cluster(struct btrfs_free_cluster *cluster);
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u64 btrfs_alloc_from_cluster(struct btrfs_block_group_cache *block_group,
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struct btrfs_free_cluster *cluster, u64 bytes,
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u64 min_start, u64 *max_extent_size);
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int btrfs_return_cluster_to_free_space(
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struct btrfs_block_group_cache *block_group,
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struct btrfs_free_cluster *cluster);
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int btrfs_trim_block_group(struct btrfs_block_group_cache *block_group,
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u64 *trimmed, u64 start, u64 end, u64 minlen);
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/* Support functions for runnint our sanity tests */
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#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
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int test_add_free_space_entry(struct btrfs_block_group_cache *cache,
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u64 offset, u64 bytes, bool bitmap);
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int test_check_exists(struct btrfs_block_group_cache *cache,
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u64 offset, u64 bytes);
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#endif
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#endif
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