From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: radix-tree: fix comment about "exceptional" bits
The bottom two bits of radix tree entries are reserved for special use by
the radix tree code itself. A comment detailing their usage was added by:
commit 3bcadd6fa6c4 ("radix-tree: free up the bottom bit of exceptional
entries for reuse")
This comment states that if the bottom two bits are '11', this means that
this is a locked exceptional entry.
It turns out that this bit combination was never actually used. Radix tree
locking for DAX was indeed implemented, but it actually used the third LSB:
/* We use lowest available exceptional entry bit for locking */
#define RADIX_DAX_ENTRY_LOCK (1 << RADIX_TREE_EXCEPTIONAL_SHIFT)
This locking code was also made specific to the DAX code instead of being
generally implemented in radix-tree.h.
So, fix the comment.
Link: http://lkml.kernel.org/r/1468997731-2155-1-git-send-email-ross.zwisler@xxxxxxxxxxxxxxx
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Reviewed-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/radix-tree.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN include/linux/radix-tree.h~radix-tree-fix-comment-about-exceptional-bits include/linux/radix-tree.h
--- a/include/linux/radix-tree.h~radix-tree-fix-comment-about-exceptional-bits
+++ a/include/linux/radix-tree.h
@@ -35,7 +35,7 @@
* 00 - data pointer
* 01 - internal entry
* 10 - exceptional entry
- * 11 - locked exceptional entry
+ * 11 - this bit combination is currently unused/reserved
*
* The internal entry may be a pointer to the next level in the tree, a
* sibling entry, or an indicator that the entry in this slot has been moved
_
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