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    Subject[PATCH 4.4 05/65] padata: ensure padata_do_serial() runs on the correct CPU
    Date
    From: Mathias Krause <minipli@googlemail.com>

    commit 350ef88e7e922354f82a931897ad4a4ce6c686ff upstream.

    If the algorithm we're parallelizing is asynchronous we might change
    CPUs between padata_do_parallel() and padata_do_serial(). However, we
    don't expect this to happen as we need to enqueue the padata object into
    the per-cpu reorder queue we took it from, i.e. the same-cpu's parallel
    queue.

    Ensure we're not switching CPUs for a given padata object by tracking
    the CPU within the padata object. If the serial callback gets called on
    the wrong CPU, defer invoking padata_reorder() via a kernel worker on
    the CPU we're expected to run on.

    Signed-off-by: Mathias Krause <minipli@googlemail.com>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
    Cc: Ben Hutchings <ben@decadent.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    include/linux/padata.h | 2 ++
    kernel/padata.c | 20 +++++++++++++++++++-
    2 files changed, 21 insertions(+), 1 deletion(-)

    --- a/include/linux/padata.h
    +++ b/include/linux/padata.h
    @@ -37,6 +37,7 @@
    * @list: List entry, to attach to the padata lists.
    * @pd: Pointer to the internal control structure.
    * @cb_cpu: Callback cpu for serializatioon.
    + * @cpu: Cpu for parallelization.
    * @seq_nr: Sequence number of the parallelized data object.
    * @info: Used to pass information from the parallel to the serial function.
    * @parallel: Parallel execution function.
    @@ -46,6 +47,7 @@ struct padata_priv {
    struct list_head list;
    struct parallel_data *pd;
    int cb_cpu;
    + int cpu;
    int info;
    void (*parallel)(struct padata_priv *padata);
    void (*serial)(struct padata_priv *padata);
    --- a/kernel/padata.c
    +++ b/kernel/padata.c
    @@ -132,6 +132,7 @@ int padata_do_parallel(struct padata_ins
    padata->cb_cpu = cb_cpu;

    target_cpu = padata_cpu_hash(pd);
    + padata->cpu = target_cpu;
    queue = per_cpu_ptr(pd->pqueue, target_cpu);

    spin_lock(&queue->parallel.lock);
    @@ -375,10 +376,21 @@ void padata_do_serial(struct padata_priv
    int cpu;
    struct padata_parallel_queue *pqueue;
    struct parallel_data *pd;
    + int reorder_via_wq = 0;

    pd = padata->pd;

    cpu = get_cpu();
    +
    + /* We need to run on the same CPU padata_do_parallel(.., padata, ..)
    + * was called on -- or, at least, enqueue the padata object into the
    + * correct per-cpu queue.
    + */
    + if (cpu != padata->cpu) {
    + reorder_via_wq = 1;
    + cpu = padata->cpu;
    + }
    +
    pqueue = per_cpu_ptr(pd->pqueue, cpu);

    spin_lock(&pqueue->reorder.lock);
    @@ -395,7 +407,13 @@ void padata_do_serial(struct padata_priv

    put_cpu();

    - padata_reorder(pd);
    + /* If we're running on the wrong CPU, call padata_reorder() via a
    + * kernel worker.
    + */
    + if (reorder_via_wq)
    + queue_work_on(cpu, pd->pinst->wq, &pqueue->reorder_work);
    + else
    + padata_reorder(pd);
    }
    EXPORT_SYMBOL(padata_do_serial);


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