On 2018/9/19 下午2:59, Qu Wenruo wrote:
> In the following case, we could trigger a use-after-free bug:
>
> CPU0 | CPU1
> -------------------------------------------------------------------------
> btrfs_remove_delayed_node | btrfs_get_delayed_node
> |- delayed_node = | |- node = btrfs_inode->delayed_node;
> | btrfs_inode->delayed_node | |
> |- btrfs_release_delaedy_node() | |
> |- ref_count_dev_and_test() | |
> |- kmem_cache_free() | |
> Now delayed node is freed | |
> | |- refcount_inc(&node->refs)
>
> In that case sine delayed_node is using kmem cache, such use-after-free
> bug won't directly cause problem, but could leads to corrupted data
> structure of other kmem cache user.
>
> Fix it by adding btrfs_inode::delayed_node_lock to protect such
> operation.
>
> Reported-by: sunny.s.zhang <sunny.s.zhang@xxxxxxxxxx>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> Please don't merge this patch yet.
False alert.
The performance degradation is a false alert, and it's pretty awkward.
Before this test run, I refilled TEST_DEV with a special file layout
(for my qgroup balance test) to increase balance/qgroup overhead.
And the file layout also turns out to be pretty heavy for btrfs check,
which makes the test time increase.
Since it's a false alert, the RFC tag is no longer needed.
Thanks,
Qu
>
> The patch caused random slow down for a lot of quick test cases.
> Old tests can be executed in 1s or so now randomly needs near 20s.
>
> It looks like the spin_lock() with root->inode_lock hold is causing the
> problem but I can't see what's going wrong.
> As the operation done with @delayed_node_lock hold is literatly tiny.
>
> Any comment on this is welcomed.
> ---
> fs/btrfs/btrfs_inode.h | 2 ++
> fs/btrfs/delayed-inode.c | 18 +++++++++++++++---
> fs/btrfs/inode.c | 1 +
> 3 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
> index 1343ac57b438..c2f054223588 100644
> --- a/fs/btrfs/btrfs_inode.h
> +++ b/fs/btrfs/btrfs_inode.h
> @@ -175,6 +175,8 @@ struct btrfs_inode {
> */
> unsigned defrag_compress;
>
> + /* lock for grabbing/freeing @delayed_node */
> + spinlock_t delayed_node_lock;
> struct btrfs_delayed_node *delayed_node;
>
> /* File creation time. */
> diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
> index f51b509f2d9b..16c405e54930 100644
> --- a/fs/btrfs/delayed-inode.c
> +++ b/fs/btrfs/delayed-inode.c
> @@ -68,19 +68,24 @@ static struct btrfs_delayed_node *btrfs_get_delayed_node(
> u64 ino = btrfs_ino(btrfs_inode);
> struct btrfs_delayed_node *node;
>
> - node = READ_ONCE(btrfs_inode->delayed_node);
> + spin_lock(&btrfs_inode->delayed_node_lock);
> + node = btrfs_inode->delayed_node;
> if (node) {
> refcount_inc(&node->refs);
> + spin_unlock(&btrfs_inode->delayed_node_lock);
> return node;
> }
> + spin_unlock(&btrfs_inode->delayed_node_lock);
>
> spin_lock(&root->inode_lock);
> node = radix_tree_lookup(&root->delayed_nodes_tree, ino);
>
> if (node) {
> + spin_lock(&btrfs_inode->delayed_node_lock);
> if (btrfs_inode->delayed_node) {
> refcount_inc(&node->refs); /* can be accessed */
> BUG_ON(btrfs_inode->delayed_node != node);
> + spin_unlock(&btrfs_inode->delayed_node_lock);
> spin_unlock(&root->inode_lock);
> return node;
> }
> @@ -108,6 +113,7 @@ static struct btrfs_delayed_node *btrfs_get_delayed_node(
> node = NULL;
> }
>
> + spin_unlock(&btrfs_inode->delayed_node_lock);
> spin_unlock(&root->inode_lock);
> return node;
> }
> @@ -152,7 +158,9 @@ static struct btrfs_delayed_node *btrfs_get_or_create_delayed_node(
> radix_tree_preload_end();
> goto again;
> }
> + spin_lock(&btrfs_inode->delayed_node_lock);
> btrfs_inode->delayed_node = node;
> + spin_unlock(&btrfs_inode->delayed_node_lock);
> spin_unlock(&root->inode_lock);
> radix_tree_preload_end();
>
> @@ -1279,11 +1287,15 @@ void btrfs_remove_delayed_node(struct btrfs_inode *inode)
> {
> struct btrfs_delayed_node *delayed_node;
>
> - delayed_node = READ_ONCE(inode->delayed_node);
> - if (!delayed_node)
> + spin_lock(&inode->delayed_node_lock);
> + delayed_node = inode->delayed_node;
> + if (!delayed_node) {
> + spin_unlock(&inode->delayed_node_lock);
> return;
> + }
>
> inode->delayed_node = NULL;
> + spin_unlock(&inode->delayed_node_lock);
> btrfs_release_delayed_node(delayed_node);
> }
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 9357a19d2bff..f438be5fecaf 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -9177,6 +9177,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
> ei->last_log_commit = 0;
>
> spin_lock_init(&ei->lock);
> + spin_lock_init(&ei->delayed_node_lock);
> ei->outstanding_extents = 0;
> if (sb->s_magic != BTRFS_TEST_MAGIC)
> btrfs_init_metadata_block_rsv(fs_info, &ei->block_rsv,
>
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