* [PATCH] btrfs-progs: do not reclaim extent buffer
@ 2014-09-30 14:40 Naohiro Aota
0 siblings, 0 replies; only message in thread
From: Naohiro Aota @ 2014-09-30 14:40 UTC (permalink / raw)
To: linux-btrfs; +Cc: bo.li.liu
We should kill free_some_buffers() to stop reclaiming extent buffers or
we will hit a problem described below.
As of commit 53ee1bccf99cd5b474fe1aa857b7dd176e3a1407, we are not
counting a reference for tree->lru anymore. However free_some_buffers()
is still left and is reclaiming extent buffers whose @refs == 1. This
cause extent buffers to be reclaimed unintentionally. Thus the following
steps could happen:
1. A buffer at address A is reclaimed by free_some_buffers()
(address A is also free()ed)
2. Some code call alloc_extent_buffer()
3. Address A is assigned to newly allocated buffer
4. You see a buffer pointed by A suddenly changed its content
This problem is also pointed out here and it has a reproducer:
https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg36703.html
This commit drop free_some_buffers() and related variables, and also it
modify extent_io_tree_cleanup() to catch non-free'ed buffers properly.
Signed-off-by: Naohiro Aota <naota@elisp.net>
---
extent_io.c | 37 +++----------------------------------
1 file changed, 3 insertions(+), 34 deletions(-)
diff --git a/extent_io.c b/extent_io.c
index 1df377d..425af8a 100644
--- a/extent_io.c
+++ b/extent_io.c
@@ -30,9 +30,6 @@
#include "ctree.h"
#include "volumes.h"
-static u64 cache_soft_max = 1024 * 1024 * 256;
-static u64 cache_hard_max = 1 * 1024 * 1024 * 1024;
-
void extent_io_tree_init(struct extent_io_tree *tree)
{
cache_tree_init(&tree->state);
@@ -77,12 +74,9 @@ void extent_io_tree_cleanup(struct extent_io_tree *tree)
while(!list_empty(&tree->lru)) {
eb = list_entry(tree->lru.next, struct extent_buffer, lru);
- if (eb->refs != 1) {
- fprintf(stderr, "extent buffer leak: "
- "start %llu len %u\n",
- (unsigned long long)eb->start, eb->len);
- eb->refs = 1;
- }
+ fprintf(stderr, "extent buffer leak: "
+ "start %llu len %u\n",
+ (unsigned long long)eb->start, eb->len);
free_extent_buffer(eb);
}
@@ -541,30 +535,6 @@ out:
return ret;
}
-static int free_some_buffers(struct extent_io_tree *tree)
-{
- u32 nrscan = 0;
- struct extent_buffer *eb;
- struct list_head *node, *next;
-
- if (tree->cache_size < cache_soft_max)
- return 0;
-
- list_for_each_safe(node, next, &tree->lru) {
- eb = list_entry(node, struct extent_buffer, lru);
- if (eb->refs == 1 && !(eb->flags & EXTENT_DIRTY)) {
- free_extent_buffer(eb);
- if (tree->cache_size < cache_hard_max)
- break;
- } else {
- list_move_tail(&eb->lru, &tree->lru);
- }
- if (nrscan++ > 64 && tree->cache_size < cache_hard_max)
- break;
- }
- return 0;
-}
-
static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
u64 bytenr, u32 blocksize)
{
@@ -589,7 +559,6 @@ static struct extent_buffer *__alloc_extent_buffer(struct extent_io_tree *tree,
eb->cache_node.size = blocksize;
INIT_LIST_HEAD(&eb->recow);
- free_some_buffers(tree);
ret = insert_cache_extent(&tree->cache, &eb->cache_node);
if (ret) {
free(eb);
--
2.1.1
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