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From: Jan Schmidt <list.btrfs@jan-o-sch.net>
To: Chris Mason <chris.mason@oracle.com>,
	Mark Fasheh <mfasheh@suse.de>,
	linux-btrfs@vger.kernel.org, Josef Bacik <josef@redhat.com>
Subject: Re: [PATCH 3/3] btrfs: extended inode refs
Date: Thu, 10 May 2012 10:23:28 +0200	[thread overview]
Message-ID: <4FAB7B00.4090302@jan-o-sch.net> (raw)
In-Reply-To: <20120509170228.GA4025@shiny>

On Wed, May 09, 2012 at 19:02 (+0200), Chris Mason wrote:
>>>> +
>>>> +	while (1) {
>>>> +		ret = btrfs_find_one_extref(fs_root, inum, offset, path, &iref2,
>>>> +					    &offset);
>>>> +		if (ret < 0)
>>>> +			break;
>>>> +		if (ret) {
>>>> +			ret = found ? 0 : -ENOENT;
>>>> +			break;
>>>> +		}
>>>> +		++found;
>>>> +
>>>> +		slot = path->slots[0];
>>>> +		eb = path->nodes[0];
>>>> +		/* make sure we can use eb after releasing the path */
>>>> +		atomic_inc(&eb->refs);
>>>
>>> You need a blocking read lock here, too. Grab it before releasing the path.
> 
> If you're calling btrfs_search_slot, it will give you a blocking lock
> on the leaf.  If you set path->leave_spinning before the call, you'll
> have a spinning lock on the leaf.
> 
> If you unlock a block that you got from a path (like eb =
> path->nodes[0]), the path structure has a flag for each level that
> indicates if that block was locked or not.  See btrfs_release_path().
> So, don't fiddle the locks without fiddling the paths.
> 
> You can switch from spinning to/from blocking without touching the path, it
> figures that out.

Note that we're releasing the path shortly after. My suggestion was to
grab an *additional* read lock after atomic_inc(&eb->refs) (probably
better extent_buffer_get(eb)) and before btrfs_path_release().

An alternative would be to set path->locks[0] to NULL, which would
btrfs_release_path prevent from unlocking it, kidnapping its lock for
our purpose. But I much prefer the open coded solution.

-Jan

  reply	other threads:[~2012-05-10  8:23 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-05 20:09 [PATCH 0/3] " Mark Fasheh
2012-04-05 20:09 ` [PATCH 1/3] " Mark Fasheh
2012-04-12 13:08   ` Jan Schmidt
2012-04-24 22:23     ` Mark Fasheh
2012-04-25 10:19       ` Jan Schmidt
2012-04-05 20:09 ` [PATCH 2/3] " Mark Fasheh
2012-04-12 13:08   ` Jan Schmidt
2012-05-03 23:12     ` Mark Fasheh
2012-05-04 11:39       ` David Sterba
2012-04-12 15:53   ` Jan Schmidt
2012-05-01 18:39     ` Mark Fasheh
2012-04-05 20:09 ` [PATCH 3/3] " Mark Fasheh
2012-04-12 17:59   ` Jan Schmidt
2012-04-12 18:38     ` Jan Schmidt
2012-05-08 22:57     ` Mark Fasheh
2012-05-09 17:02       ` Chris Mason
2012-05-10  8:23         ` Jan Schmidt [this message]
2012-05-10 13:35           ` Chris Mason
2012-04-05 21:13 ` [PATCH 0/3] " Jeff Mahoney
2012-04-11 13:11   ` Jan Schmidt
2012-04-11 13:29     ` Jan Schmidt
2012-04-12 16:11     ` Chris Mason
2012-04-12 16:19       ` Mark Fasheh
2012-04-06  1:24 ` Liu Bo
2012-04-06  2:12   ` Liu Bo
2012-05-21 21:46 Mark Fasheh
2012-05-21 21:46 ` [PATCH 3/3] " Mark Fasheh
2012-07-06 14:57   ` Jan Schmidt
2012-07-09 20:24     ` Mark Fasheh
2012-08-08 18:55 [PATCH 0/3] " Mark Fasheh
2012-08-08 18:55 ` [PATCH 3/3] " Mark Fasheh
2012-08-15  8:46   ` Jan Schmidt

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