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padata: ensure padata_do_serial() runs on the correct CPU

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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>
This commit is contained in:
Mathias Krause 2017-09-08 20:57:11 +02:00 committed by Herbert Xu
parent cf5868c8a2
commit 350ef88e7e
2 changed files with 21 additions and 1 deletions
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2
include/linux/padata.h
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@ -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);

20
kernel/padata.c
View file

@ -131,6 +131,7 @@ int padata_do_parallel(struct padata_instance *pinst,
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);
@ -363,10 +364,21 @@ void padata_do_serial(struct padata_priv *padata)
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);
@ -376,7 +388,13 @@ void padata_do_serial(struct padata_priv *padata)
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);