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btrfs-progs: do not reclaim extent buffer

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We should kill free_some_buffers() to stop reclaiming extent buffers or
we will hit a problem described below.

As of commit 53ee1bccf9, 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>
Signed-off-by: David Sterba <dsterba@suse.cz>
This commit is contained in:
Naohiro Aota 2014-09-30 23:40:56 +09:00 committed by David Sterba
parent 9ecbbe30ec
commit f32d749e66
1 changed files with 3 additions and 34 deletions
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37
extent_io.c
View File

@ -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);