linux-kernel - Re: [PATCH] maple_tree: Remove rcu_read_lock() from mt

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Message-ID: <ZsUehuMKf1dfRfJI@casper.infradead.org>
Date: Tue, 20 Aug 2024 23:53:58 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Hillf Danton <hdanton@...a.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	maple-tree@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...nel.org>,
	syzbot+036af2f0c7338a33b0cd@...kaller.appspotmail.com
Subject: Re: [PATCH] maple_tree: Remove rcu_read_lock() from mt_validate()

On Wed, Aug 21, 2024 at 06:38:45AM +0800, Hillf Danton wrote:

Hillf, your email client is STILL broken.  It's using the same message
ID as the email it's replying to, which causes all kinds of problems.
Please fix it or change to a different client.

> On Tue, 20 Aug 2024 13:54:17 -0400 "Liam R. Howlett" <Liam.Howlett@...cle.com>
> > 
> > The write lock should be held when validating the tree to avoid updates
> > racing with checks.  Holding the rcu read lock during a large tree
> > validation may also cause a prolonged rcu read window.
> > 
> >From the rcu stall's view, holding spin lock plays the same role of rcu
> read lock, so what are you fixing by simply dropping rcu read lock?

He's not holding a spinlock, he's holding a mutex, which has very
different properties.