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    Subject[RFC v1 3/5] seq_file: Add percpu seq_hlist helpers with locking iterators
    Date
    Introduce a variant of the seq_hlist helpers for iterating seq_hlist
    are protected by perpcu spinlocks.

    Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
    Cc: Jeff Layton <jlayton@poochiereds.net>
    Cc: "J. Bruce Fields" <bfields@fieldses.org>
    Cc: Alexander Viro <viro@zeniv.linux.org.uk>
    ---
    fs/seq_file.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++
    include/linux/seq_file.h | 13 ++++++++
    2 files changed, 96 insertions(+)

    diff --git a/fs/seq_file.c b/fs/seq_file.c
    index 555f821..56adfdb 100644
    --- a/fs/seq_file.c
    +++ b/fs/seq_file.c
    @@ -966,3 +966,86 @@ seq_hlist_next_percpu(void *v, struct hlist_head __percpu *head,
    return NULL;
    }
    EXPORT_SYMBOL(seq_hlist_next_percpu);
    +
    +/**
    + * seq_hlist_start_precpu_locked - start an iteration of a percpu hlist array
    + * @head: pointer to percpu array of struct hlist_heads
    + * @lock: pointer to percpu spinlock which protects @head
    + * @cpu: pointer to cpu "cursor"
    + * @pos: start position of sequence
    + *
    + * Called at seq_file->op->start().
    + */
    +struct hlist_node *
    +seq_hlist_start_percpu_locked(struct hlist_head __percpu *head,
    + spinlock_t __percpu *lock, int *cpu, loff_t pos)
    +{
    + struct hlist_node *node;
    +
    + for_each_possible_cpu(*cpu) {
    + spin_lock(per_cpu_ptr(lock, *cpu));
    + hlist_for_each(node, per_cpu_ptr(head, *cpu)) {
    + if (pos-- == 0)
    + return node;
    + }
    + spin_unlock(per_cpu_ptr(lock, *cpu));
    + }
    + return NULL;
    +}
    +EXPORT_SYMBOL(seq_hlist_start_percpu_locked);
    +
    +/**
    + * seq_hlist_next_percpu_locked - move to the next position of the percpu hlist array
    + * @v: pointer to current hlist_node
    + * @head: pointer to percpu array of struct hlist_heads
    + * @lock: pointer to percpu spinlock which protects @head
    + * @cpu: pointer to cpu "cursor"
    + * @pos: start position of sequence
    + *
    + * Called at seq_file->op->next().
    + */
    +struct hlist_node *
    +seq_hlist_next_percpu_locked(void *v, struct hlist_head __percpu *head,
    + spinlock_t __percpu *lock,
    + int *cpu, loff_t *pos)
    +{
    + struct hlist_node *node = v;
    +
    + ++*pos;
    +
    + if (node->next)
    + return node->next;
    +
    + spin_unlock(per_cpu_ptr(lock, *cpu));
    +
    + for (*cpu = cpumask_next(*cpu, cpu_possible_mask); *cpu < nr_cpu_ids;
    + *cpu = cpumask_next(*cpu, cpu_possible_mask)) {
    + struct hlist_head *bucket;
    +
    + spin_lock(per_cpu_ptr(lock, *cpu));
    + bucket = per_cpu_ptr(head, *cpu);
    +
    + if (!hlist_empty(bucket))
    + return bucket->first;
    +
    + spin_unlock(per_cpu_ptr(lock, *cpu));
    + }
    + return NULL;
    +}
    +EXPORT_SYMBOL(seq_hlist_next_percpu_locked);
    +
    +/**
    + * seq_hlist_stop_percpu_locked - stop iterating over the percpu hlist array
    + * @v: pointer to current hlist_node
    + * @lock: pointer to percpu spinlock which protects @head
    + * @cpu: pointer to cpu "cursor"
    + *
    + * Called at seq_file->op->stop().
    + */
    +void
    +seq_hlist_stop_percpu_locked(void *v, spinlock_t __percpu *lock, int *cpu)
    +{
    + if (v)
    + spin_unlock(per_cpu_ptr(lock, *cpu));
    +}
    +EXPORT_SYMBOL(seq_hlist_stop_percpu_locked);
    diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
    index afbb1fd..6419ac4 100644
    --- a/include/linux/seq_file.h
    +++ b/include/linux/seq_file.h
    @@ -184,4 +184,17 @@ extern struct hlist_node *seq_hlist_start_percpu(struct hlist_head __percpu *hea

    extern struct hlist_node *seq_hlist_next_percpu(void *v, struct hlist_head __percpu *head, int *cpu, loff_t *pos);

    +extern struct hlist_node *seq_hlist_start_percpu_locked(
    + struct hlist_head __percpu *head,
    + spinlock_t __percpu *lock,
    + int *cpu, loff_t pos);
    +
    +extern struct hlist_node *seq_hlist_next_percpu_locked(
    + void *v, struct hlist_head __percpu *head,
    + spinlock_t __percpu *lock,
    + int *cpu, loff_t *pos);
    +
    +extern void seq_hlist_stop_percpu_locked(
    + void *v, spinlock_t __percpu *lock, int *cpu);
    +
    #endif
    --
    2.1.0


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