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Date: Tue, 28 Jul 2026 06:38:38 +0200
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Brian Foster <bfoster@redhat.com>,
	Carlos Maiolino <cem@kernel.org>, linux-xfs@vger.kernel.org
Subject: Re: [PATCH 02/12] xfs: consolidate buffer locking in
 xfs_buf_get_map
Message-ID: <20260728043838.GA20064@lst.de>
References: <20260715145147.95654-1-hch@lst.de> <20260715145147.95654-3-hch@lst.de> <aljY0uI6jY8y2b3Z@bfoster> <20260717085950.GA32056@lst.de> <alo4doLYG7BzuCfO@bfoster> <20260720075902.GA18645@lst.de> <20260724164218.GP2901224@frogsfrogsfrogs>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Jul 24, 2026 at 09:42:18AM -0700, Darrick J. Wong wrote:
> It could emphasize that b_lockref is used to make rcu lookups safe
> against a freed buffer whereas b_sema is used to prevent racing threads
> from doing anything non-trivial with the buffer once they've gotten
> themselves a lockref, and that's why the comment is obsolete and can go
> away.
> 
> Or modify the comment?

I've picked up a slight variant of this, thanks.

> Is there a subtlety here that the buffer creator might not be the one to
> read the buffer contents in from disk if another thread happens to find
> the buffer in the cache, take b_sema, notice that it's not XBF_DONE, and
> start the read on its own?

Yes, but it doesn't really matter.