From 1bd845bcb41d5b7f83745e0cb99273eb376f2ec5 Mon Sep 17 00:00:00 2001 From: Mathias Krause Date: Fri, 8 Sep 2017 20:57:09 +0200 Subject: padata: set cpu_index of unused CPUs to -1 The parallel queue per-cpu data structure gets initialized only for CPUs in the 'pcpu' CPU mask set. This is not sufficient as the reorder timer may run on a different CPU and might wrongly decide it's the target CPU for the next reorder item as per-cpu memory gets memset(0) and we might be waiting for the first CPU in cpumask.pcpu, i.e. cpu_index 0. Make the '__this_cpu_read(pd->pqueue->cpu_index) == next_queue->cpu_index' compare in padata_get_next() fail in this case by initializing the cpu_index member of all per-cpu parallel queues. Use -1 for unused ones. Signed-off-by: Mathias Krause Signed-off-by: Herbert Xu --- kernel/padata.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/padata.c b/kernel/padata.c index 868f947166d7..1b9b4bac4a9b 100644 --- a/kernel/padata.c +++ b/kernel/padata.c @@ -384,8 +384,14 @@ static void padata_init_pqueues(struct parallel_data *pd) struct padata_parallel_queue *pqueue; cpu_index = 0; - for_each_cpu(cpu, pd->cpumask.pcpu) { + for_each_possible_cpu(cpu) { pqueue = per_cpu_ptr(pd->pqueue, cpu); + + if (!cpumask_test_cpu(cpu, pd->cpumask.pcpu)) { + pqueue->cpu_index = -1; + continue; + } + pqueue->pd = pd; pqueue->cpu_index = cpu_index; cpu_index++; -- cgit v1.2.3 From cf5868c8a22dc2854b96e9569064bb92365549ca Mon Sep 17 00:00:00 2001 From: Mathias Krause Date: Fri, 8 Sep 2017 20:57:10 +0200 Subject: padata: ensure the reorder timer callback runs on the correct CPU The reorder timer function runs on the CPU where the timer interrupt was handled which is not necessarily one of the CPUs of the 'pcpu' CPU mask set. Ensure the padata_reorder() callback runs on the correct CPU, which is one in the 'pcpu' CPU mask set and, preferrably, the next expected one. Do so by comparing the current CPU with the expected target CPU. If they match, call padata_reorder() right away. If they differ, schedule a work item on the target CPU that does the padata_reorder() call for us. Signed-off-by: Mathias Krause Signed-off-by: Herbert Xu --- include/linux/padata.h | 2 ++ kernel/padata.c | 43 ++++++++++++++++++++++++++++++++++++++++++- 2 files changed, 44 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/include/linux/padata.h b/include/linux/padata.h index 2f9c1f93b1ce..5c0175bbc179 100644 --- a/include/linux/padata.h +++ b/include/linux/padata.h @@ -85,6 +85,7 @@ struct padata_serial_queue { * @swork: work struct for serialization. * @pd: Backpointer to the internal control structure. * @work: work struct for parallelization. + * @reorder_work: work struct for reordering. * @num_obj: Number of objects that are processed by this cpu. * @cpu_index: Index of the cpu. */ @@ -93,6 +94,7 @@ struct padata_parallel_queue { struct padata_list reorder; struct parallel_data *pd; struct work_struct work; + struct work_struct reorder_work; atomic_t num_obj; int cpu_index; }; diff --git a/kernel/padata.c b/kernel/padata.c index 1b9b4bac4a9b..b4066147bce4 100644 --- a/kernel/padata.c +++ b/kernel/padata.c @@ -275,11 +275,51 @@ static void padata_reorder(struct parallel_data *pd) return; } +static void invoke_padata_reorder(struct work_struct *work) +{ + struct padata_parallel_queue *pqueue; + struct parallel_data *pd; + + local_bh_disable(); + pqueue = container_of(work, struct padata_parallel_queue, reorder_work); + pd = pqueue->pd; + padata_reorder(pd); + local_bh_enable(); +} + static void padata_reorder_timer(unsigned long arg) { struct parallel_data *pd = (struct parallel_data *)arg; + unsigned int weight; + int target_cpu, cpu; - padata_reorder(pd); + cpu = get_cpu(); + + /* We don't lock pd here to not interfere with parallel processing + * padata_reorder() calls on other CPUs. We just need any CPU out of + * the cpumask.pcpu set. It would be nice if it's the right one but + * it doesn't matter if we're off to the next one by using an outdated + * pd->processed value. + */ + weight = cpumask_weight(pd->cpumask.pcpu); + target_cpu = padata_index_to_cpu(pd, pd->processed % weight); + + /* ensure to call the reorder callback on the correct CPU */ + if (cpu != target_cpu) { + struct padata_parallel_queue *pqueue; + struct padata_instance *pinst; + + /* The timer function is serialized wrt itself -- no locking + * needed. + */ + pinst = pd->pinst; + pqueue = per_cpu_ptr(pd->pqueue, target_cpu); + queue_work_on(target_cpu, pinst->wq, &pqueue->reorder_work); + } else { + padata_reorder(pd); + } + + put_cpu(); } static void padata_serial_worker(struct work_struct *serial_work) @@ -399,6 +439,7 @@ static void padata_init_pqueues(struct parallel_data *pd) __padata_list_init(&pqueue->reorder); __padata_list_init(&pqueue->parallel); INIT_WORK(&pqueue->work, padata_parallel_worker); + INIT_WORK(&pqueue->reorder_work, invoke_padata_reorder); atomic_set(&pqueue->num_obj, 0); } } -- cgit v1.2.3 From 350ef88e7e922354f82a931897ad4a4ce6c686ff Mon Sep 17 00:00:00 2001 From: Mathias Krause Date: Fri, 8 Sep 2017 20:57:11 +0200 Subject: padata: ensure padata_do_serial() runs on the correct CPU 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 Signed-off-by: Herbert Xu --- include/linux/padata.h | 2 ++ kernel/padata.c | 20 +++++++++++++++++++- 2 files changed, 21 insertions(+), 1 deletion(-) (limited to 'kernel') diff --git a/include/linux/padata.h b/include/linux/padata.h index 5c0175bbc179..5d13d25da2c8 100644 --- 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); diff --git a/kernel/padata.c b/kernel/padata.c index b4066147bce4..f262c9a4e70a 100644 --- a/kernel/padata.c +++ b/kernel/padata.c @@ -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); -- cgit v1.2.3