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Revision c269a24ce057abfc31130960e96ab197ef6ab196 authored by Jakub Kicinski on 06 January 2021, 18:40:06 UTC, committed by Jakub Kicinski on 09 January 2021, 03:27:41 UTC 
net: make free_netdev() more lenient with unregistering devices
 
There are two flavors of handling netdev registration:
 - ones called without holding rtnl_lock: register_netdev() and
   unregister_netdev(); and
 - those called with rtnl_lock held: register_netdevice() and
   unregister_netdevice().

While the semantics of the former are pretty clear, the same can't
be said about the latter. The netdev_todo mechanism is utilized to
perform some of the device unregistering tasks and it hooks into
rtnl_unlock() so the locked variants can't actually finish the work.
In general free_netdev() does not mix well with locked calls. Most
drivers operating under rtnl_lock set dev->needs_free_netdev to true
and expect core to make the free_netdev() call some time later.

The part where this becomes most problematic is error paths. There is
no way to unwind the state cleanly after a call to register_netdevice(),
since unreg can't be performed fully without dropping locks.

Make free_netdev() more lenient, and defer the freeing if device
is being unregistered. This allows error paths to simply call
free_netdev() both after register_netdevice() failed, and after
a call to unregister_netdevice() but before dropping rtnl_lock.

Simplify the error paths which are currently doing gymnastics
around free_netdev() handling.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
1 parent 2b446e6
Raw File
blk-mq-cpumap.c 
// SPDX-License-Identifier: GPL-2.0
/*
 * CPU <-> hardware queue mapping helpers
 *
 * Copyright (C) 2013-2014 Jens Axboe
 */
#include <linux/kernel.h>
#include <linux/threads.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/cpu.h>

#include <linux/blk-mq.h>
#include "blk.h"
#include "blk-mq.h"

static int queue_index(struct blk_mq_queue_map *qmap,
		       unsigned int nr_queues, const int q)
{
	return qmap->queue_offset + (q % nr_queues);
}

static int get_first_sibling(unsigned int cpu)
{
	unsigned int ret;

	ret = cpumask_first(topology_sibling_cpumask(cpu));
	if (ret < nr_cpu_ids)
		return ret;

	return cpu;
}

int blk_mq_map_queues(struct blk_mq_queue_map *qmap)
{
	unsigned int *map = qmap->mq_map;
	unsigned int nr_queues = qmap->nr_queues;
	unsigned int cpu, first_sibling, q = 0;

	for_each_possible_cpu(cpu)
		map[cpu] = -1;

	/*
	 * Spread queues among present CPUs first for minimizing
	 * count of dead queues which are mapped by all un-present CPUs
	 */
	for_each_present_cpu(cpu) {
		if (q >= nr_queues)
			break;
		map[cpu] = queue_index(qmap, nr_queues, q++);
	}

	for_each_possible_cpu(cpu) {
		if (map[cpu] != -1)
			continue;
		/*
		 * First do sequential mapping between CPUs and queues.
		 * In case we still have CPUs to map, and we have some number of
		 * threads per cores then map sibling threads to the same queue
		 * for performance optimizations.
		 */
		if (q < nr_queues) {
			map[cpu] = queue_index(qmap, nr_queues, q++);
		} else {
			first_sibling = get_first_sibling(cpu);
			if (first_sibling == cpu)
				map[cpu] = queue_index(qmap, nr_queues, q++);
			else
				map[cpu] = map[first_sibling];
		}
	}

	return 0;
}
EXPORT_SYMBOL_GPL(blk_mq_map_queues);

/**
 * blk_mq_hw_queue_to_node - Look up the memory node for a hardware queue index
 * @qmap: CPU to hardware queue map.
 * @index: hardware queue index.
 *
 * We have no quick way of doing reverse lookups. This is only used at
 * queue init time, so runtime isn't important.
 */
int blk_mq_hw_queue_to_node(struct blk_mq_queue_map *qmap, unsigned int index)
{
	int i;

	for_each_possible_cpu(i) {
		if (index == qmap->mq_map[i])
			return cpu_to_node(i);
	}

	return NUMA_NO_NODE;
}
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