Commit f8b703da authored Aug 18, 2015 by Fan Li Committed by Jaegeuk Kim Aug 21, 2015

f2fs: fix to update cached_en of extent tree properly



In f2fs_lookup_extent_tree, et->cached_en was read and updated with only
read lock held,
it could cause __lookup_extent_tree within return entirely wrong
extent_node, if other
thread update et->cached_en just before __lookup_extent_tree return.

However, there are two things about this patch that need to be noticed:
1. It does no good to arrange the order of concurrent read/write, the result
would still
be random in such case.
2. It's built on this assumption: the mix up of reads and writes on a single
pointer would
not make the pointer partially wrong at any time. Please let me know if I'm
wrong, thx.

Signed-off-by: Fan li <fanofcode.li@samsung.com>
Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

parent 217940d4

fs/f2fs/extent_cache.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -85,13 +85,13 @@ static struct extent_node __lookup_extent_tree(struct extent_tree et,
		unsigned int fofs)
		{
		struct rb_node *node = et->root.rb_node;
		struct extent_node *en;
		struct extent_node *en = et->cached_en;

		if (et->cached_en) {
		struct extent_info *cei = &et->cached_en->ei;
		if (en) {
		struct extent_info *cei = &en->ei;

		if (cei->fofs <= fofs && cei->fofs + cei->len > fofs)
		return et->cached_en;
		return en;
		}

		while (node) {