linux-kernel - Re: [PATCH 1/4] change get_super_thawed() to use sb_start/end

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Message-ID: <20150714104922.GC24369@quack.suse.cz>
Date:	Tue, 14 Jul 2015 12:49:22 +0200
From:	Jan Kara <jack@...e.cz>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Daniel Wagner <daniel.wagner@...-carit.de>,
	Davidlohr Bueso <dave@...olabs.net>,
	Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] change get_super_thawed() to use sb_start/end_write()

On Mon 13-07-15 23:25:48, Oleg Nesterov wrote:
> Preparation. get_super_thawed() can do sb_start/end_write() with
> the same effect, we are going to kill sb_writers->wait_unfrozen.
> ---
>  fs/super.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/super.c b/fs/super.c
> index 928c20f..5ea0edd 100644
> --- a/fs/super.c
> +++ b/fs/super.c
> @@ -621,8 +621,8 @@ struct super_block *get_super_thawed(struct block_device *bdev)
>  		if (!s || s->s_writers.frozen == SB_UNFROZEN)
>  			return s;
>  		up_read(&s->s_umount);
> -		wait_event(s->s_writers.wait_unfrozen,
> -			   s->s_writers.frozen == SB_UNFROZEN);
> +		sb_start_write(s);
> +		sb_end_intwrite(s);

This is definitely buggy - you need to start and end freeze protection at
the same level...

									Honza

>  		put_super(s);
>  	}
>  }
> -- 
> 1.5.5.1
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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