mm: readahead scan lockless

radix_tree_next_hole() is implemented as a series of radix_tree_lookup()s.
So it can be called locklessly, under rcu_read_lock().

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/readahead.c b/mm/readahead.c
index d8723a5..77e8ddf 100644 (file)
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -382,9 +382,9 @@ ondemand_readahead(struct address_space *mapping,
        if (hit_readahead_marker) {
                pgoff_t start;
 
-               read_lock_irq(&mapping->tree_lock);
-               start = radix_tree_next_hole(&mapping->page_tree, offset, max+1);
-               read_unlock_irq(&mapping->tree_lock);
+               rcu_read_lock();
+               start = radix_tree_next_hole(&mapping->page_tree, offset,max+1);
+               rcu_read_unlock();
 
                if (!start || start - offset > max)
                        return 0;