linux-kernel - Re: [PATCH AUTOSEL 4.19 14/14] fs/dcache: Disable preemption on i_dir_seq write side on PREEMPT

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Message-ID: <20220813134334.GA24517@duo.ucw.cz>
Date:   Sat, 13 Aug 2022 15:43:34 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Oleg.Karfich@...o.com, Thomas Gleixner <tglx@...utronix.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.19 14/14] fs/dcache: Disable preemption on
 i_dir_seq write side on PREEMPT_RT

Hi!

> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> 
> [ Upstream commit cf634d540a29018e8d69ab1befb7e08182bc6594 ]
> 
> i_dir_seq is a sequence counter with a lock which is represented by the
> lowest bit. The writer atomically updates the counter which ensures that it
> can be modified by only one writer at a time. This requires preemption to
> be disabled across the write side critical section.
> 
> On !PREEMPT_RT kernels this is implicit by the caller acquiring
> dentry::lock. On PREEMPT_RT kernels spin_lock() does not disable preemption

This should not be applied to 4.19 as CONFIG_PREEMPT_RT does not exist
there.

Best regards,
								Pavel
-- 
 'DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk'
 'HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany'


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