On 27.04.2018 12:58, ethanwu wrote:
> In preivous patch:
> Btrfs: kill trans in run_delalloc_nocow and btrfs_cross_ref_exist
> We avoid starting btrfs transaction and get this information from
> fs_info->running_transaction directly.
>
> When accessing running_transaction in check_delayed_ref, there's a
> chance that current transaction will be freed by commit transaction
> after the NULL pointer check of running_transaction is passed.
>
> After looking all the other places using fs_info->running_transaction,
> they are either protected by trans_lock or holding the transactions.
>
> Fix this by using trans_lock and incrementing the use_count.
Yep, looking at how ->running_transaction is set/cleared, holding the
trans_lock is correct here. However there is one point which you need to
fix.
>
> Signed-off-by: ethanwu <ethanwu@xxxxxxxxxxxx>
> ---
> fs/btrfs/extent-tree.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index c1618ab..c8fd37b 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -3149,7 +3149,11 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
> struct rb_node *node;
> int ret = 0;
>
> + spin_lock(&root->fs_info->trans_lock);
> cur_trans = root->fs_info->running_transaction;
> + if (cur_trans)
> + atomic_inc(&cur_trans->use_count);
The ->use_count is using refcount_inc now, not atomic_inc. Please base
all further upstream patches on upstream code
> + spin_unlock(&root->fs_info->trans_lock);
> if (!cur_trans)
> return 0;
>
> @@ -3158,6 +3162,7 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
> head = btrfs_find_delayed_ref_head(delayed_refs, bytenr);
> if (!head) {
> spin_unlock(&delayed_refs->lock);
> + btrfs_put_transaction(cur_trans);
> return 0;
> }
>
> @@ -3174,6 +3179,7 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
> mutex_lock(&head->mutex);
> mutex_unlock(&head->mutex);
> btrfs_put_delayed_ref_head(head);
> + btrfs_put_transaction(cur_trans);
> return -EAGAIN;
> }
> spin_unlock(&delayed_refs->lock);
> @@ -3206,6 +3212,7 @@ static noinline int check_delayed_ref(struct btrfs_root *root,
> }
> spin_unlock(&head->lock);
> mutex_unlock(&head->mutex);
> + btrfs_put_transaction(cur_trans);
> return ret;
> }
>
>
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