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authorDave Chinner <dchinner@redhat.com>2010-08-23 10:33:53 +1000
committerDave Chinner <david@fromorbit.com>2010-08-23 10:33:53 +1000
commit144dcfc01221e1a79fa47ca897df7d5e3ab298e6 (patch)
tree70b0d0bf73815fb242502a562da3a8c7667843ba /drivers/usb
parentb6dd08652e2b70e73661c4975ae46398066c06f8 (diff)
radix-tree: radix_tree_range_tag_if_tagged() can set incorrect tags
Commit ebf8aa44beed48cd17893a83d92a4403e5f9d9e2 ("radix-tree: omplement function radix_tree_range_tag_if_tagged") does not safely set tags on on intermediate tree nodes. The code walks down the tree setting tags before it has fully resolved the path to the leaf under the assumption there will be a leaf slot with the tag set in the range it is searching. Unfortunately, this is not a valid assumption - we can abort after setting a tag on an intermediate node if we overrun the number of tags we are allowed to set in a batch, or stop scanning because we we have passed the last scan index before we reach a leaf slot with the tag we are searching for set. As a result, we can leave the function with tags set on intemediate nodes which can be tripped over later by tag-based lookups. The result of these stale tags is that lookup may end prematurely or livelock because the lookup cannot make progress. The fix for the problem involves reocrding the traversal path we take to the leaf nodes, and only propagating the tags back up the tree once the tag is set in the leaf node slot. We are already recording the path for efficient traversal, so there is no additional overhead to do the intermediately node tag setting in this manner. This fixes a radix tree lookup livelock triggered by the new writeback sync livelock avoidance code introduced in commit f446daaea9d4a420d16c606f755f3689dcb2d0ce ("mm: implement writeback livelock avoidance using page tagging"). Signed-off-by: Dave Chinner <dchinner@redhat.com> Acked-by: Jan Kara <jack@suse.cz>
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