Any comment for the following patch?
On wed, 09 May 2012 11:39:36 +0800, Miao Xie wrote:
> On tue, 8 May 2012 16:56:27 +0800, Daniel J Blueman wrote:
>> Delayed allocation ref mutexes are taken [1] inside
>> btrfs_commit_transaction. A later call fails and jumps to the
>> cleanup_transaction label (transaction.c:1501) with these mutexes
>> still held causing deadlock [2] when they are reacquired.
>>
>> Either we can introduce an earlier label (cleanup_transaction_lock)
>> and function to unlock these mutexes or can tweak
>> btrfs_destroy_delayed_refs to conditionally use mutex_try_lock.
>>
>> What is the suggested approach?
>
> I think we can unlock those mutexes at the suitable place.
> Could you try this patch?
>
> Title:[PATCH] Btrfs: fix deadlock when the process of delayed refs fails
>
> Delayed ref mutexes are taken inside btrfs_commit_transaction. A later call
> fails and jumps to the cleanup_transaction label with these mutexes still held
> causing deadlock when they are reacquired.
>
> Fix this problem by unlocking those mutexes at the suitable place.
>
> Reported-by: Daniel J Blueman <dan...@quora.org>
> Signed-off-by: Miao Xie <mi...@cn.fujitsu.com>
> ---
> fs/btrfs/delayed-ref.c | 8 ++++++++
> fs/btrfs/delayed-ref.h | 7 +++++++
> fs/btrfs/extent-tree.c | 24 ++++++++++++++++++------
> 3 files changed, 33 insertions(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
> index 69f22e3..bc43c89 100644
> --- a/fs/btrfs/delayed-ref.c
> +++ b/fs/btrfs/delayed-ref.c
> @@ -310,6 +310,14 @@ again:
> return 1;
> }
>
> +void btrfs_release_ref_cluster(struct list_head *cluster)
> +{
> + struct list_head *pos, *q;
> +
> + list_for_each_safe(pos, q, cluster)
> + list_del_init(pos);
> +}
> +
> /*
> * helper function to update an extent delayed ref in the
> * rbtree. existing and update must both have the same
> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h
> index d8f244d..bd9c316 100644
> --- a/fs/btrfs/delayed-ref.h
> +++ b/fs/btrfs/delayed-ref.h
> @@ -192,8 +192,15 @@ struct btrfs_delayed_ref_head *
> btrfs_find_delayed_ref_head(struct btrfs_trans_handle *trans, u64 bytenr);
> int btrfs_delayed_ref_lock(struct btrfs_trans_handle *trans,
> struct btrfs_delayed_ref_head *head);
> +static inline void btrfs_delayed_ref_unlock(struct btrfs_trans_handle *trans,
> + struct btrfs_delayed_ref_head *head)
> +{
> + mutex_unlock(&head->mutex);
> +}
> +
> int btrfs_find_ref_cluster(struct btrfs_trans_handle *trans,
> struct list_head *cluster, u64 search_start);
> +void btrfs_release_ref_cluster(struct list_head *cluster);
>
> struct seq_list {
> struct list_head list;
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 49fd7b6..973379a 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -2157,7 +2157,6 @@ static int run_one_delayed_ref(struct
> btrfs_trans_handle *trans,
> node->num_bytes);
> }
> }
> - mutex_unlock(&head->mutex);
> return ret;
> }
>
> @@ -2302,14 +2301,13 @@ static noinline int run_clustered_refs(struct
> btrfs_trans_handle *trans,
> if (ret) {
> printk(KERN_DEBUG "btrfs:
> run_delayed_extent_op returned %d\n", ret);
> spin_lock(&delayed_refs->lock);
> + btrfs_delayed_ref_unlock(trans,
> + locked_ref);
> return ret;
> }
>
> goto next;
> }
> -
> - list_del_init(&locked_ref->cluster);
> - locked_ref = NULL;
> }
>
> ref->in_tree = 0;
> @@ -2325,11 +2323,24 @@ static noinline int run_clustered_refs(struct
> btrfs_trans_handle *trans,
>
> ret = run_one_delayed_ref(trans, root, ref, extent_op,
> must_insert_reserved);
> -
> - btrfs_put_delayed_ref(ref);
> kfree(extent_op);
> count++;
>
> + /*
> + * If this node is a head, we will pick the next head to deal
> + * with. If there is something wrong when we process the
> + * delayed ref, we will end our operation. So in these two
> + * cases, we have to unlock the head and drop it from the
> + * cluster list before we release it though the code is ugly.
> + */
> + if (btrfs_delayed_ref_is_head(ref) || ret) {
> + btrfs_delayed_ref_unlock(trans, locked_ref);
> + list_del_init(&locked_ref->cluster);
> + locked_ref = NULL;
> + }
> +
> + btrfs_put_delayed_ref(ref);
> +
> if (ret) {
> printk(KERN_DEBUG "btrfs: run_one_delayed_ref returned
> %d\n", ret);
> spin_lock(&delayed_refs->lock);
> @@ -2450,6 +2461,7 @@ again:
>
> ret = run_clustered_refs(trans, root, &cluster);
> if (ret < 0) {
> + btrfs_release_ref_cluster(&cluster);
> spin_unlock(&delayed_refs->lock);
> btrfs_abort_transaction(trans, root, ret);
> return ret;
--
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