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Date: Tue, 14 Jul 2015 12:49:22 +0200
From: Jan Kara <jack@suse.cz>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Daniel Wagner <daniel.wagner@bmw-carit.de>,
        Davidlohr Bueso <dave@stgolabs.net>, Ingo Molnar <mingo@redhat.com>,
        Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/4] change get_super_thawed() to use sb_start/end_write()
Message-ID: <20150714104922.GC24369@quack.suse.cz>
References: <20150713212536.GA13855@redhat.com>
 <20150713212548.GA13873@redhat.com>
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User-Agent: Mutt/1.5.21 (2010-09-15)
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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@suse.cz>
SUSE Labs, CR