From: David Sterba <dsterba@suse.cz>
To: Nikolay Borisov <nborisov@suse.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: [PATCH] btrfs: Rename btrfs_join_transaction_nolock
Date: Thu, 10 Oct 2019 18:26:37 +0200 [thread overview]
Message-ID: <20191010162637.GX2751@twin.jikos.cz> (raw)
In-Reply-To: <20191008174306.2395-1-nborisov@suse.com>
On Tue, Oct 08, 2019 at 08:43:06PM +0300, Nikolay Borisov wrote:
> This function is used only during the final phase of freespace cache
> writeout. This is necessary since using the plain btrfs_join_transaction
> api is deadlock prone. The deadlock looks like:
>
> T1:
> btrfs_commit_Transaction
> commit_cowonly_roots
> btrfs_write_dirty_block_groups
> btrfs_wait_cache_io
> __btrfs_wait_cache_io
> btrfs_wait_ordered_range <-- Triggers ordered IO for freespace
> inode and blocks transaction commit until freespace cache
> writeout.
>
> T2: <-- after T1 has triggered the writeout
> finish_ordered_fn
> btrfs_finish_ordered_io
> btrfs_join_transaction <--- this would block waiting for current
> transaction to commit, but since trans commit is waiting for this
> writeout to finish.
>
> The special purpose functions prevents it by simply skipping the "wait
> for writeout" since it's guaranteed the transaction won't proceed until
> we are done.
>
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Added to misc-next, thanks.
prev parent reply other threads:[~2019-10-10 16:26 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-08 17:43 [PATCH] btrfs: Rename btrfs_join_transaction_nolock Nikolay Borisov
2019-10-09 1:16 ` Qu Wenruo
2019-10-10 16:26 ` David Sterba [this message]
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