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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-rdma.c 
// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2017 Sagi Grimberg.
 */
#include <linux/blk-mq.h>
#include <linux/blk-mq-rdma.h>
#include <rdma/ib_verbs.h>

/**
 * blk_mq_rdma_map_queues - provide a default queue mapping for rdma device
 * @map:	CPU to hardware queue map.
 * @dev:	rdma device to provide a mapping for.
 * @first_vec:	first interrupt vectors to use for queues (usually 0)
 *
 * This function assumes the rdma device @dev has at least as many available
 * interrupt vetors as @set has queues.  It will then query it's affinity mask
 * and built queue mapping that maps a queue to the CPUs that have irq affinity
 * for the corresponding vector.
 *
 * In case either the driver passed a @dev with less vectors than
 * @set->nr_hw_queues, or @dev does not provide an affinity mask for a
 * vector, we fallback to the naive mapping.
 */
int blk_mq_rdma_map_queues(struct blk_mq_queue_map *map,
		struct ib_device *dev, int first_vec)
{
	const struct cpumask *mask;
	unsigned int queue, cpu;

	for (queue = 0; queue < map->nr_queues; queue++) {
		mask = ib_get_vector_affinity(dev, first_vec + queue);
		if (!mask)
			goto fallback;

		for_each_cpu(cpu, mask)
			map->mq_map[cpu] = map->queue_offset + queue;
	}

	return 0;

fallback:
	return blk_mq_map_queues(map);
}
EXPORT_SYMBOL_GPL(blk_mq_rdma_map_queues);
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