linux-kernel - Re: [PATCHv4 01/17] zram: switch to non-atomic entry locking

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Message-ID: <y7d7otbyqolio7767wbetli2fmv2ugja6bwriz32dncqvnsmj7@4jrdyk5gnch2>
Date: Thu, 6 Feb 2025 17:29:12 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, Minchan Kim <minchan@...nel.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Hillf Danton <hdanton@...a.com>, 
	Mike Galbraith <umgwanakikbuti@...il.com>
Subject: Re: [PATCHv4 01/17] zram: switch to non-atomic entry locking

On (25/02/06 09:26), Sebastian Andrzej Siewior wrote:
> On 2025-02-06 17:17:41 [+0900], Sergey Senozhatsky wrote:
> > > Okay. So there are requirements for the sleeping lock. A mutex isn't
> > > fitting the requirement because it is too large I guess.
> > 
> > Correct.
> 
> I would nice to state this why a generic locking implementation can not
> be used. From what I have seen it should play along with RT nicely.

Will do.

> > > > wait_on_bit_lock() has might_sleep().
> > > 
> > > My point exactly. This makes the WARN_ON_ONCE() obsolete.
> > 
> > Right, might_sleep() can be disabled, as far as I understand,
> > via CONFIG_DEBUG_ATOMIC_SLEEP, unlike WARN_ON_ONCE().  But I
> > can drop it and then just rely on might_sleep(), should be
> > enough.
> 
> It should be enough. mutex_lock(), down() and so on relies solely on it.
> As I said, preemptible() only works on preemptible kernels if it comes
> to the preemption counter on and !preemptible kernels with enabled
> debugging.

Ack.