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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>
This commit is contained in:
Fan Li 2015-08-18 17:13:13 +08:00 committed by Jaegeuk Kim
parent 217940d4f0
commit f8b703da2c
1 changed files with 4 additions and 4 deletions
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8
fs/f2fs/extent_cache.c
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@ -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) {