btrfs: fix deadlock when cloning inline extents and low on available space
There are a few cases where cloning an inline extent requires copying data into a page of the destination inode. For these cases we are allocating the required data and metadata space while holding a leaf locked. This can result in a deadlock when we are low on available space because allocating the space may flush delalloc and two deadlock scenarios can happen: 1) When starting writeback for an inode with a very small dirty range that fits in an inline extent, we deadlock during the writeback when trying to insert the inline extent, at cow_file_range_inline(), if the extent is going to be located in the leaf for which we are already holding a read lock; 2) After successfully starting writeback, for non-inline extent cases, the async reclaim thread will hang waiting for an ordered extent to complete if the ordered extent completion needs to modify the leaf for which the clone task is holding a read lock (for adding or replacing file extent items). So the cloning task will wait forever on the async reclaim thread to make progress, which in turn is waiting for the ordered extent completion which in turn is waiting to acquire a write lock on the same leaf. So fix this by making sure we release the path (and therefore the leaf) every time we need to copy the inline extent's data into a page of the destination inode, as by that time we do not need to have the leaf locked. Fixes: 05a5a762 ("Btrfs: implement full reflink support for inline extents") CC: stable@vger.kernel.org # 5.10+ Signed-off-by:Filipe Manana <fdmanana@suse.com> Signed-off-by:
David Sterba <dsterba@suse.com>
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