• Josef Bacik's avatar
    btrfs: fix readdir deadlock with pagefault · 23b5ec74
    Josef Bacik authored
    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: default avatarJosef Bacik <jbacik@fb.com>
    Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
    [ copy the deadlock scenario to changelog ]
    Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
    23b5ec74
ctree.h 127 KB