btrfs: fix readdir deadlock with pagefault
Readdir does dir_emit while under the btree lock. dir_emit can trigger the page fault which means we can deadlock. Fix this by allocating a buffer on opening a directory and copying the readdir into this buffer and doing dir_emit from outside of the tree lock. Thread A readdir <holding tree lock> dir_emit <page fault> down_read(mmap_sem) Thread B mmap write down_write(mmap_sem) page_mkwrite wait_ordered_extents Process C finish_ordered_extent insert_reserved_file_extent try to lock leaf <hang> Signed-off-by: NJosef Bacik <jbacik@fb.com> Reviewed-by: NDavid Sterba <dsterba@suse.com> [ copy the deadlock scenario to changelog ] Signed-off-by: NDavid Sterba <dsterba@suse.com>
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