On Tue, 07 Dec 2010 20:01:49 +0100 Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> wrote: > I got the same warning as reported by Arun Bhanu in "[BUG?] [Ext4] INFO: > suspicious rcu_dereference_check() usage" during memory hotplug test on > 2.6.37-rc5, see below. > > migrate_pages() -> unmap_and_move() only calls rcu_read_lock() for anonymous > pages, as introduced by git commit 989f89c57e6361e7d16fbd9572b5da7d313b073d. > This should be ok, as the comment suggests, so the warning is probably a > false positive. Eventually, migrate_page_move_mapping() will call > radix_tree_deref_slot() with tree_lock held, but w/o rcu_read_lock() for > non-anonymous pages. > > As suggested by Milton before, a new version of radix_tree_deref_slot that > uses rcu_dereference_protected could help, if this is a false positive, or > maybe the rcu_read_lock() should be called for all pages, not just anonymous. > Any thoughts? > Hmm, in radix_tree_deref_slot() comment, 140 * For use with radix_tree_lookup_slot(). Caller must hold tree at least read 141 * locked across slot lookup and dereference. More likely, will be used with 142 * radix_tree_replace_slot(), as well, so caller will hold tree write locked. racy update must not happen. rcu_dereference_protected() sounds nice. Thanks, -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
