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Subject[PATCH 4.14 05/59] 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
@@ -133,6 +133,7 @@ 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);
@@ -376,10 +377,21 @@ 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);
@@ -396,7 +408,13 @@ 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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