linux-kernel - Re: [PATCH 4/4] change sb_writers to use percpu_rw

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Message-ID: <20150722213437.GA20617@redhat.com>
Date:	Wed, 22 Jul 2015 23:34:37 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Al Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Jan Kara <jack@...e.cz>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] change sb_writers to use percpu_rw_semaphore

Sorry for noise, but let me say just in case...

On 07/22, Oleg Nesterov wrote:
>
> Perhaps we should also cleanup the usage of ->frozen. It would be
> better to set/clear (say) SB_FREEZE_WRITE with the corresponding
> write-lock held. Currently freeze_super() has to set SB_FREEZE_WRITE
> before sb_wait_write(SB_FREEZE_WRITE) to avoid the race with itself,

"Currently" means "after this change". Before this change we obviously
need to increment ->frozen before sb_wait_write().

> The "From now on, no new normal writers
> can start" removed by this patch was not really correct.

Yes, it was confusing even without this change.

Oleg.

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