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Revision ae1e206b806ccc490dadff59af8a7a2477b32884 authored by Josef Bacik on 07 August 2012, 20:00:32 UTC, committed by Chris Mason on 28 August 2012, 20:53:38 UTC 
Btrfs: allow delayed refs to be merged
 
Daniel Blueman reported a bug with fio+balance on a ramdisk setup.
Basically what happens is the balance relocates a tree block which will drop
the implicit refs for all of its children and adds a full backref.  Once the
block is relocated we have to add the implicit refs back, so when we cow the
block again we add the implicit refs for its children back.  The problem
comes when the original drop ref doesn't get run before we add the implicit
refs back.  The delayed ref stuff will specifically prefer ADD operations
over DROP to keep us from freeing up an extent that will have references to
it, so we try to add the implicit ref before it is actually removed and we
panic.  This worked fine before because the add would have just canceled the
drop out and we would have been fine.  But the backref walking work needs to
be able to freeze the delayed ref stuff in time so we have this ever
increasing sequence number that gets attached to all new delayed ref updates
which makes us not merge refs and we run into this issue.

So to fix this we need to merge delayed refs.  So everytime we run a
clustered ref we need to try and merge all of its delayed refs.  The backref
walking stuff locks the delayed ref head before processing, so if we have it
locked we are safe to merge any refs inside of the sequence number.  If
there is no sequence number we can merge all refs.  Doing this not only
fixes our bug but keeps the delayed ref code from adding and removing
useless refs and batching together multiple refs into one search instead of
one search per delayed ref, which will really help our commit times.  I ran
this with Daniels test and 276 and I haven't seen any problems.  Thanks,

Reported-by: Daniel J Blueman <daniel@quora.org>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
1 parent 5a24e84
Raw File
rpmsg_client_sample.c 
/*
 * Remote processor messaging - sample client driver
 *
 * Copyright (C) 2011 Texas Instruments, Inc.
 * Copyright (C) 2011 Google, Inc.
 *
 * Ohad Ben-Cohen <ohad@wizery.com>
 * Brian Swetland <swetland@google.com>
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/rpmsg.h>

#define MSG		"hello world!"
#define MSG_LIMIT	100

static void rpmsg_sample_cb(struct rpmsg_channel *rpdev, void *data, int len,
						void *priv, u32 src)
{
	int ret;
	static int rx_count;

	dev_info(&rpdev->dev, "incoming msg %d (src: 0x%x)\n", ++rx_count, src);

	print_hex_dump(KERN_DEBUG, __func__, DUMP_PREFIX_NONE, 16, 1,
		       data, len,  true);

	/* samples should not live forever */
	if (rx_count >= MSG_LIMIT) {
		dev_info(&rpdev->dev, "goodbye!\n");
		return;
	}

	/* send a new message now */
	ret = rpmsg_send(rpdev, MSG, strlen(MSG));
	if (ret)
		dev_err(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
}

static int rpmsg_sample_probe(struct rpmsg_channel *rpdev)
{
	int ret;

	dev_info(&rpdev->dev, "new channel: 0x%x -> 0x%x!\n",
					rpdev->src, rpdev->dst);

	/* send a message to our remote processor */
	ret = rpmsg_send(rpdev, MSG, strlen(MSG));
	if (ret) {
		dev_err(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
		return ret;
	}

	return 0;
}

static void __devexit rpmsg_sample_remove(struct rpmsg_channel *rpdev)
{
	dev_info(&rpdev->dev, "rpmsg sample client driver is removed\n");
}

static struct rpmsg_device_id rpmsg_driver_sample_id_table[] = {
	{ .name	= "rpmsg-client-sample" },
	{ },
};
MODULE_DEVICE_TABLE(rpmsg, rpmsg_driver_sample_id_table);

static struct rpmsg_driver rpmsg_sample_client = {
	.drv.name	= KBUILD_MODNAME,
	.drv.owner	= THIS_MODULE,
	.id_table	= rpmsg_driver_sample_id_table,
	.probe		= rpmsg_sample_probe,
	.callback	= rpmsg_sample_cb,
	.remove		= __devexit_p(rpmsg_sample_remove),
};

static int __init rpmsg_client_sample_init(void)
{
	return register_rpmsg_driver(&rpmsg_sample_client);
}
module_init(rpmsg_client_sample_init);

static void __exit rpmsg_client_sample_fini(void)
{
	unregister_rpmsg_driver(&rpmsg_sample_client);
}
module_exit(rpmsg_client_sample_fini);

MODULE_DESCRIPTION("Remote processor messaging sample client driver");
MODULE_LICENSE("GPL v2");
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