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When logging an inode in full mode, or when logging xattrs or when logging the dir index items of a directory, we are modifying the log tree while holding a read lock on a leaf from the fs/subvolume tree. This can lead to a deadlock in rare circumstances, but it is a real possibility, and it was recently reported by syzbot with the following trace from lockdep: WARNING: possible circular locking dependency detected 6.1.0-rc5-next-20221116-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor.1/16154 is trying to acquire lock: ffff88807e3084a0 (&delayed_node->mutex){+.+.}-{3:3}, at: __btrfs_release_delayed_node.part.0+0xa1/0xf30 fs/btrfs/delayed-inode.c:256 but task is already holding lock: ffff88807df33078 (btrfs-log-00){++++}-{3:3}, at: __btrfs_tree_lock+0x32/0x3d0 fs/btrfs/locking.c:197 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (btrfs-log-00){++++}-{3:3}: down_read_nested+0x9e/0x450 kernel/locking/rwsem.c:1634 __btrfs_tree_read_lock+0x32/0x350 fs/btrfs/locking.c:135 btrfs_tree_read_lock fs/btrfs/locking.c:141 [inline] btrfs_read_lock_root_node+0x82/0x3a0 fs/btrfs/locking.c:280 btrfs_search_slot_get_root fs/btrfs/ctree.c:1678 [inline] btrfs_search_slot+0x3ca/0x2c70 fs/btrfs/ctree.c:1998 btrfs_lookup_csum+0x116/0x3f0 fs/btrfs/file-item.c:209 btrfs_csum_file_blocks+0x40e/0x1370 fs/btrfs/file-item.c:1021 log_csums.isra.0+0x244/0x2d0 fs/btrfs/tree-log.c:4258 copy_items.isra.0+0xbfb/0xed0 fs/btrfs/tree-log.c:4403 copy_inode_items_to_log+0x13d6/0x1d90 fs/btrfs/tree-log.c:5873 btrfs_log_inode+0xb19/0x4680 fs/btrfs/tree-log.c:6495 btrfs_log_inode_parent+0x890/0x2a20 fs/btrfs/tree-log.c:6982 btrfs_log_dentry_safe+0x59/0x80 fs/btrfs/tree-log.c:7083 btrfs_sync_file+0xa41/0x13c0 fs/btrfs/file.c:1921 vfs_fsync_range+0x13e/0x230 fs/sync.c:188 generic_write_sync include/linux/fs.h:2856 [inline] iomap_dio_complete+0x73a/0x920 fs/iomap/direct-io.c:128 btrfs_direct_write fs/btrfs/file.c:1536 [inline] btrfs_do_write_iter+0xba2/0x1470 fs/btrfs/file.c:1668 call_write_iter include/linux/fs.h:2160 [inline] do_iter_readv_writev+0x20b/0x3b0 fs/read_write.c:735 do_iter_write+0x182/0x700 fs/read_write.c:861 vfs_iter_write+0x74/0xa0 fs/read_write.c:902 iter_file_splice_write+0x745/0xc90 fs/splice.c:686 do_splice_from fs/splice.c:764 [inline] direct_splice_actor+0x114/0x180 fs/splice.c:931 splice_direct_to_actor+0x335/0x8a0 fs/splice.c:886 do_splice_direct+0x1ab/0x280 fs/splice.c:974 do_sendfile+0xb19/0x1270 fs/read_write.c:1255 __do_sys_sendfile64 fs/read_write.c:1323 [inline] __se_sys_sendfile64 fs/read_write.c:1309 [inline] __x64_sys_sendfile64+0x259/0x2c0 fs/read_write.c:1309 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd -> #1 (btrfs-tree-00){++++}-{3:3}: __lock_release kernel/locking/lockdep.c:5382 [inline] lock_release+0x371/0x810 kernel/locking/lockdep.c:5688 up_write+0x2a/0x520 kernel/locking/rwsem.c:1614 btrfs_tree_unlock_rw fs/btrfs/locking.h:189 [inline] btrfs_unlock_up_safe+0x1e3/0x290 fs/btrfs/locking.c:238 search_leaf fs/btrfs/ctree.c:1832 [inline] btrfs_search_slot+0x265e/0x2c70 fs/btrfs/ctree.c:2074 btrfs_insert_empty_items+0xbd/0x1c0 fs/btrfs/ctree.c:4133 btrfs_insert_delayed_item+0x826/0xfa0 fs/btrfs/delayed-inode.c:746 btrfs_insert_delayed_items fs/btrfs/delayed-inode.c:824 [inline] __btrfs_commit_inode_delayed_items fs/btrfs/delayed-inode.c:1111 [inline] __btrfs_run_delayed_items+0x280/0x590 fs/btrfs/delayed-inode.c:1153 flush_space+0x147/0xe90 fs/btrfs/space-info.c:728 btrfs_async_reclaim_metadata_space+0x541/0xc10 fs/btrfs/space-info.c:1086 process_one_work+0x9bf/0x1710 kernel/workqueue.c:2289 worker_thread+0x669/0x1090 kernel/workqueue.c:2436 kthread+0x2e8/0x3a0 kernel/kthread.c:376 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308 -> #0 (&delayed_node->mutex){+.+.}-{3:3}: check_prev_add kernel/locking/lockdep.c:3097 [inline] check_prevs_add kernel/locking/lockdep.c:3216 [inline] validate_chain kernel/locking/lockdep.c:3831 [inline] __lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5055 lock_acquire kernel/locking/lockdep.c:5668 [inline] lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633 __mutex_lock_common kernel/locking/mutex.c:603 [inline] __mutex_lock+0x12f/0x1360 kernel/locking/mutex.c:747 __btrfs_release_delayed_node.part.0+0xa1/0xf30 fs/btrfs/delayed-inode.c:256 __btrfs_release_delayed_node fs/btrfs/delayed-inode.c:251 [inline] btrfs_release_delayed_node fs/btrfs/delayed-inode.c:281 [inline] btrfs_remove_delayed_node+0x52/0x60 fs/btrfs/delayed-inode.c:1285 btrfs_evict_inode+0x511/0xf30 fs/btrfs/inode.c:5554 evict+0x2ed/0x6b0 fs/inode.c:664 dispose_list+0x117/0x1e0 fs/inode.c:697 prune_icache_sb+0xeb/0x150 fs/inode.c:896 super_cache_scan+0x391/0x590 fs/super.c:106 do_shrink_slab+0x464/0xce0 mm/vmscan.c:843 shrink_slab_memcg mm/vmscan.c:912 [inline] shrink_slab+0x388/0x660 mm/vmscan.c:991 shrink_node_memcgs mm/vmscan.c:6088 [inline] shrink_node+0x93d/0x1f30 mm/vmscan.c:6117 shrink_zones mm/vmscan.c:6355 [inline] do_try_to_free_pages+0x3b4/0x17a0 mm/vmscan.c:6417 try_to_free_mem_cgroup_pages+0x3a4/0xa70 mm/vmscan.c:6732 reclaim_high.constprop.0+0x182/0x230 mm/memcontrol.c:2393 mem_cgroup_handle_over_high+0x190/0x520 mm/memcontrol.c:2578 try_charge_memcg+0xe0c/0x12f0 mm/memcontrol.c:2816 try_charge mm/memcontrol.c:2827 [inline] charge_memcg+0x90/0x3b0 mm/memcontrol.c:6889 __mem_cgroup_charge+0x2b/0x90 mm/memcontrol.c:6910 mem_cgroup_charge include/linux/memcontrol.h:667 [inline] __filemap_add_folio+0x615/0xf80 mm/filemap.c:852 filemap_add_folio+0xaf/0x1e0 mm/filemap.c:934 __filemap_get_folio+0x389/0xd80 mm/filemap.c:1976 pagecache_get_page+0x2e/0x280 mm/folio-compat.c:104 find_or_create_page include/linux/pagemap.h:612 [inline] alloc_extent_buffer+0x2b9/0x1580 fs/btrfs/extent_io.c:4588 btrfs_init_new_buffer fs/btrfs/extent-tree.c:4869 [inline] btrfs_alloc_tree_block+0x2e1/0x1320 fs/btrfs/extent-tree.c:4988 __btrfs_cow_block+0x3b2/0x1420 fs/btrfs/ctree.c:440 btrfs_cow_block+0x2fa/0x950 fs/btrfs/ctree.c:595 btrfs_search_slot+0x11b0/0x2c70 fs/btrfs/ctree.c:2038 btrfs_update_root+0xdb/0x630 fs/btrfs/root-tree.c:137 update_log_root fs/btrfs/tree-log.c:2841 [inline] btrfs_sync_log+0xbfb/0x2870 fs/btrfs/tree-log.c:3064 btrfs_sync_file+0xdb9/0x13c0 fs/btrfs/file.c:1947 vfs_fsync_range+0x13e/0x230 fs/sync.c:188 generic_write_sync include/linux/fs.h:2856 [inline] iomap_dio_complete+0x73a/0x920 fs/iomap/direct-io.c:128 btrfs_direct_write fs/btrfs/file.c:1536 [inline] btrfs_do_write_iter+0xba2/0x1470 fs/btrfs/file.c:1668 call_write_iter include/linux/fs.h:2160 [inline] do_iter_readv_writev+0x20b/0x3b0 fs/read_write.c:735 do_iter_write+0x182/0x700 fs/read_write.c:861 vfs_iter_write+0x74/0xa0 fs/read_write.c:902 iter_file_splice_write+0x745/0xc90 fs/splice.c:686 do_splice_from fs/splice.c:764 [inline] direct_splice_actor+0x114/0x180 fs/splice.c:931 splice_direct_to_actor+0x335/0x8a0 fs/splice.c:886 do_splice_direct+0x1ab/0x280 fs/splice.c:974 do_sendfile+0xb19/0x1270 fs/read_write.c:1255 __do_sys_sendfile64 fs/read_write.c:1323 [inline] __se_sys_sendfile64 fs/read_write.c:1309 [inline] __x64_sys_sendfile64+0x259/0x2c0 fs/read_write.c:1309 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd other info that might help us debug this: Chain exists of: &delayed_node->mutex --> btrfs-tree-00 --> btrfs-log-00 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(btrfs-log-00); lock(btrfs-tree-00); lock(btrfs-log-00); lock(&delayed_node->mutex); Holding a read lock on a leaf from a fs/subvolume tree creates a nasty lock dependency when we are COWing extent buffers for the log tree and we have two tasks modifying the log tree, with each one in one of the following 2 scenarios: 1) Modifying the log tree triggers an extent buffer allocation while holding a write lock on a parent extent buffer from the log tree. Allocating the pages for an extent buffer, or the extent buffer struct, can trigger inode eviction and finally the inode eviction will trigger a release/remove of a delayed node, which requires taking the delayed node's mutex; 2) Allocating a metadata extent for a log tree can trigger the async reclaim thread and make us wait for it to release enough space and unblock our reservation ticket. The reclaim thread can start flushing delayed items, and that in turn results in the need to lock delayed node mutexes and in the need to write lock extent buffers of a subvolume tree - all this while holding a write lock on the parent extent buffer in the log tree. So one task in scenario 1) running in parallel with another task in scenario 2) could lead to a deadlock, one wanting to lock a delayed node mutex while having a read lock on a leaf from the subvolume, while the other is holding the delayed node's mutex and wants to write lock the same subvolume leaf for flushing delayed items. Fix this by cloning the leaf of the fs/subvolume tree, release/unlock the fs/subvolume leaf and use the clone leaf instead. Reported-by: syzbot+9b7c21f486f5e7f8d029@syzkaller.appspotmail.com Link: https://lore.kernel.org/linux-btrfs/000000000000ccc93c05edc4d8cf@google.com/ CC: stable@vger.kernel.org # 6.0+ Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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