linux-kernel - Re: [PATCH 1/5] xfs: use kfree_rcu_mightsleep to free the perag structures

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Message-ID: <20240822034248.GC32681@lst.de>
Date: Thu, 22 Aug 2024 05:42:48 +0200
From: Christoph Hellwig <hch@....de>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Christoph Hellwig <hch@....de>,
	Chandan Babu R <chandan.babu@...cle.com>,
	Matthew Wilcox <willy@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/5] xfs: use kfree_rcu_mightsleep to free the perag
 structures

On Wed, Aug 21, 2024 at 09:19:39AM -0700, Darrick J. Wong wrote:
> I started wondering, have you seen any complaints from might_sleep when
> freeing pags after a failed growfs?

No, why would I?  We're not freeing perags with a spinlock held there.

> Then I wondered if growfs_data
> could actually take any locks that would prevent sleeping, which led me
> to another question: why do growfs_{data,log} hold m_growlock but
> growfs_rt doesn't?  Is that actually safe?

As far as I can tell growfs_rt is missing a m_growlock critical section
and right now we allow parallel calls to growfs_rt, which could lead
to unexpected results.