Messages in this thread | | | Subject | Re: [BUG] fs: btrfs: several possible ABBA deadlocks | From | Nikolay Borisov <> | Date | Mon, 29 Nov 2021 16:37:14 +0200 |
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On 29.11.21 г. 2:34, Josef Bacik wrote: > On Sat, Nov 27, 2021 at 04:23:37PM +0800, Jia-Ju Bai wrote: >> Hello, >> >> My static analysis tool reports several possible ABBA deadlocks in the btrfs >> module in Linux 5.10: >> >> # DEADLOCK 1: >> __clear_extent_bit() >> spin_lock(&tree->lock); --> Line 733 (Lock A) >> split_state() >> btrfs_split_delalloc_extent() >> spin_lock(&BTRFS_I(inode)->lock); --> Line 1870 (Lock B) >> >> btrfs_inode_safe_disk_i_size_write() >> spin_lock(&BTRFS_I(inode)->lock); --> Line 53 (Lock B) >> find_contiguous_extent_bit() >> spin_lock(&tree->lock); --> Line 1620 (Lock A) >> >> When __clear_extent_bit() and btrfs_inode_safe_disk_i_size_write() are >> concurrently executed, the deadlock can occur. >> >> # DEADLOCK 2: >> __set_extent_bit() >> spin_lock(&tree->lock); --> Line 995 (Lock A) >> set_state_bits() >> btrfs_set_delalloc_extent() >> spin_lock(&BTRFS_I(inode)->lock); --> Line 2007 or 2017 or 2029 (Lock >> B) >> >> btrfs_inode_safe_disk_i_size_write() >> spin_lock(&BTRFS_I(inode)->lock); --> Line 53 (Lock B) >> find_contiguous_extent_bit() >> spin_lock(&tree->lock); --> Line 1620 (Lock A) >> >> When __set_extent_bit() and btrfs_inode_safe_disk_i_size_write() are >> concurrently executed, the deadlock can occur. >> >> # DEADLOCK 3: >> convert_extent_bit() >> spin_lock(&tree->lock); --> Line 1241 (Lock A) >> set_state_bits() >> btrfs_set_delalloc_extent() >> spin_lock(&BTRFS_I(inode)->lock); --> Line 2007 or 2017 or 2029 (Lock >> B) >> >> btrfs_inode_safe_disk_i_size_write() >> spin_lock(&BTRFS_I(inode)->lock); --> Line 53 (Lock B) >> find_contiguous_extent_bit() >> spin_lock(&tree->lock); --> Line 1620 (Lock A) >> >> When convert_extent_bit() and btrfs_inode_safe_disk_i_size_write() are >> concurrently executed, the deadlock can occur. >> >> I am not quite sure whether these possible deadlocks are real and how to fix >> them if they are real. >> Any feedback would be appreciated, thanks :) >> > > Hey Jia-Ju, > > This is pretty good work, unfortunately it's wrong but it's in a subtle way that > a tool wouldn't be able to catch. The btrfs_inode_safe_disk_i_size_write() > helper only messes with BTRFS_I(inode)->file_extent_tree, which is separate from > the BTRFS_I(inode)->io_tree. io_tree gets the btrfs_set_delalloc_extent() stuff > called on it, but the file_extent_tree does not. The file_extent_tree has > inode->lock -> tree->lock as the locking order, whereas the file_extent_tree has > inode->lock -> tree->lock as the locking order. Thanks,
nit: did you mean to reverse tree->lock ->inode->lock for the file_extent_tree?
> > Josef >
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