On Wed, 2011-02-23 at 21:31 -0800, Hugh Dickins wrote:

The radix_tree_deref_retry() case in find_get_pages() has a strange
little excrescence, not seen in the other gang lookups: it looks like
the start of an abandoned attempt to guarantee forward progress in a
case that cannot arise.

ret should always be 0 here: if it isn't, then going back to restart
will leak references to pages already gotten.  There used to be a
comment saying nr_found is necessarily 1 here: that's not quite true,
but the radix_tree_deref_retry() case is peculiar to the entry at index
0, when we race with it being moved out of the radix_tree root or back.

Remove the worrisome two lines, add a brief comment here and in
find_get_pages_contig() and find_get_pages_tag(), and a WARN_ON
in find_get_pages() should it ever be seen elsewhere than at 0.

Signed-off-by: Hugh Dickins <hughd@google.com>

Acked-by: Peter Zijlstra <redacted>


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