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Revision 774a1221e862b343388347bac9b318767336b20b authored by Tejun Heo on 16 January 2013, 02:52:51 UTC, committed by Linus Torvalds on 16 January 2013, 17:05:33 UTC 
module, async: async_synchronize_full() on module init iff async is used
 
If the default iosched is built as module, the kernel may deadlock
while trying to load the iosched module on device probe if the probing
was running off async.  This is because async_synchronize_full() at
the end of module init ends up waiting for the async job which
initiated the module loading.

 async A				modprobe

 1. finds a device
 2. registers the block device
 3. request_module(default iosched)
					4. modprobe in userland
					5. load and init module
					6. async_synchronize_full()

Async A waits for modprobe to finish in request_module() and modprobe
waits for async A to finish in async_synchronize_full().

Because there's no easy to track dependency once control goes out to
userland, implementing properly nested flushing is difficult.  For
now, make module init perform async_synchronize_full() iff module init
has queued async jobs as suggested by Linus.

This avoids the described deadlock because iosched module doesn't use
async and thus wouldn't invoke async_synchronize_full().  This is
hacky and incomplete.  It will deadlock if async module loading nests;
however, this works around the known problem case and seems to be the
best of bad options.

For more details, please refer to the following thread.

  http://thread.gmane.org/gmane.linux.kernel/1420814

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Alex Riesen <raa.lkml@gmail.com>
Tested-by: Ming Lei <ming.lei@canonical.com>
Tested-by: Alex Riesen <raa.lkml@gmail.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 parent 406089d
Raw File
br_notify.c 
/*
 *	Device event handling
 *	Linux ethernet bridge
 *
 *	Authors:
 *	Lennert Buytenhek		<buytenh@gnu.org>
 *
 *	This program is free software; you can redistribute it and/or
 *	modify it under the terms of the GNU General Public License
 *	as published by the Free Software Foundation; either version
 *	2 of the License, or (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/rtnetlink.h>
#include <net/net_namespace.h>

#include "br_private.h"

static int br_device_event(struct notifier_block *unused, unsigned long event, void *ptr);

struct notifier_block br_device_notifier = {
	.notifier_call = br_device_event
};

/*
 * Handle changes in state of network devices enslaved to a bridge.
 *
 * Note: don't care about up/down if bridge itself is down, because
 *     port state is checked when bridge is brought up.
 */
static int br_device_event(struct notifier_block *unused, unsigned long event, void *ptr)
{
	struct net_device *dev = ptr;
	struct net_bridge_port *p;
	struct net_bridge *br;
	bool changed_addr;
	int err;

	/* register of bridge completed, add sysfs entries */
	if ((dev->priv_flags & IFF_EBRIDGE) && event == NETDEV_REGISTER) {
		br_sysfs_addbr(dev);
		return NOTIFY_DONE;
	}

	/* not a port of a bridge */
	p = br_port_get_rtnl(dev);
	if (!p)
		return NOTIFY_DONE;

	br = p->br;

	switch (event) {
	case NETDEV_CHANGEMTU:
		dev_set_mtu(br->dev, br_min_mtu(br));
		break;

	case NETDEV_CHANGEADDR:
		spin_lock_bh(&br->lock);
		br_fdb_changeaddr(p, dev->dev_addr);
		changed_addr = br_stp_recalculate_bridge_id(br);
		spin_unlock_bh(&br->lock);

		if (changed_addr)
			call_netdevice_notifiers(NETDEV_CHANGEADDR, br->dev);

		break;

	case NETDEV_CHANGE:
		br_port_carrier_check(p);
		break;

	case NETDEV_FEAT_CHANGE:
		netdev_update_features(br->dev);
		break;

	case NETDEV_DOWN:
		spin_lock_bh(&br->lock);
		if (br->dev->flags & IFF_UP)
			br_stp_disable_port(p);
		spin_unlock_bh(&br->lock);
		break;

	case NETDEV_UP:
		if (netif_carrier_ok(dev) && (br->dev->flags & IFF_UP)) {
			spin_lock_bh(&br->lock);
			br_stp_enable_port(p);
			spin_unlock_bh(&br->lock);
		}
		break;

	case NETDEV_UNREGISTER:
		br_del_if(br, dev);
		break;

	case NETDEV_CHANGENAME:
		err = br_sysfs_renameif(p);
		if (err)
			return notifier_from_errno(err);
		break;

	case NETDEV_PRE_TYPE_CHANGE:
		/* Forbid underlaying device to change its type. */
		return NOTIFY_BAD;
	}

	/* Events that may cause spanning tree to refresh */
	if (event == NETDEV_CHANGEADDR || event == NETDEV_UP ||
	    event == NETDEV_CHANGE || event == NETDEV_DOWN)
		br_ifinfo_notify(RTM_NEWLINK, p);

	return NOTIFY_DONE;
}
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