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From: Peter Zijlstra <peterz@infradead.org>
To: John Ogness <john.ogness@linutronix.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/1] fs/namespace.c: use spinlock instead of busy loop
Date: Wed, 17 Jun 2020 13:27:19 +0200	[thread overview]
Message-ID: <20200617112719.GI2531@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200617104058.14902-2-john.ogness@linutronix.de>

On Wed, Jun 17, 2020 at 12:46:58PM +0206, John Ogness wrote:
> The MNT_WRITE_HOLD flag is used to manually implement a per-cpu
> optimized rwsem using busy waiting. This implementation is a problem
> on PREEMPT_RT because write_seqlock() on @mount_lock (i.e. taking a
> spinlock) does not disable preemption. This allows a writer to
> preempt a task that has set MNT_WRITE_HOLD and thus that writer will
> live lock in __mnt_want_write() due to busy looping with preemption
> disabled.
> 

Why can't you use a regular percpu-rwsem for this?

  parent reply	other threads:[~2020-06-17 11:27 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-17 10:40 [RFC PATCH 0/1] fs: remove retry loop John Ogness
2020-06-17 10:40 ` [RFC PATCH 1/1] fs/namespace.c: use spinlock instead of busy loop John Ogness
2020-06-17 11:26   ` Peter Zijlstra
2020-06-17 11:27   ` Peter Zijlstra [this message]
2020-06-17 12:09     ` Sebastian Andrzej Siewior

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