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From: David Sterba <dsterba@suse.cz>
To: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH 2/3] btrfs: protect the fs_info->caching_block_groups differently
Date: Wed, 21 Oct 2020 17:51:59 +0200	[thread overview]
Message-ID: <20201021155159.GF6756@twin.jikos.cz> (raw)
In-Reply-To: <64816a7abd985112ddd7c44998753f72b5775a1a.1603137558.git.josef@toxicpanda.com>

On Mon, Oct 19, 2020 at 04:02:30PM -0400, Josef Bacik wrote:
> while testing another lockdep fix.  This happens because we're using the
> commit_root_sem to protect fs_info->caching_block_groups, which creates
> a dependency on the groups_sem -> commit_root_sem, which is problematic
> because we will allocate blocks while holding tree roots.  Fix this by
> making the list itself protected by the fs_info->block_group_cache_lock.

That's lacking explanation why this is supposed to be correct. Replacing
semaphore by a spin lock has implications and given that he commit root
sem does not protect a single structure or is sometimes used for context
exclusion, this requires more in the changelog and updated perhaps
comments for the locks.

  parent reply	other threads:[~2020-10-21 15:53 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-19 20:02 [PATCH 0/3] Lockdep fixes for misc-next Josef Bacik
2020-10-19 20:02 ` [PATCH 1/3] btrfs: drop the path before adding qgroup items when enabling qgroups Josef Bacik
2020-10-20  9:31   ` Filipe Manana
2020-10-21 15:19   ` David Sterba
2020-10-19 20:02 ` [PATCH 2/3] btrfs: protect the fs_info->caching_block_groups differently Josef Bacik
2020-10-20 10:10   ` Filipe Manana
2020-10-21 14:05     ` Josef Bacik
2020-10-21 16:36       ` Filipe Manana
2020-10-21 18:44         ` Josef Bacik
2020-10-21 15:51   ` David Sterba [this message]
2020-10-19 20:02 ` [PATCH 3/3] btrfs: add a helper to read the tree_root commit root for backref lookup Josef Bacik
2020-10-20 11:06   ` Filipe Manana
2020-10-21 16:13 ` [PATCH 0/3] Lockdep fixes for misc-next David Sterba

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