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Date:   Tue, 19 Mar 2019 15:58:16 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     "jianchao.wang" <jianchao.w.wang@oracle.com>
Cc:     Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
        Omar Sandoval <osandov@fb.com>, Yi Zhang <yi.zhang@redhat.com>
Subject: Re: [PATCH] sbitmap: order RW on old associated instance and setting
 clear bit
Message-ID: <20190319075815.GA28327@ming.t460p>
References: <20190319042447.27580-1-ming.lei@redhat.com>
 <9e784c48-2865-a14a-d8f4-e6c74f258f48@oracle.com>
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On Tue, Mar 19, 2019 at 01:17:31PM +0800, jianchao.wang wrote:
> Hi Ming
> 
> On 3/19/19 12:24 PM, Ming Lei wrote:
> > @@ -591,6 +591,15 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
> >  void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
> >  			 unsigned int cpu)
> >  {
> > +	/*
> > +	 * Once the clear bit is set, it will be visible to allocation
> > +	 * side.
> > +	 *
> > +	 * This memory barrier orders any READ/WRITE on the to-be-freed
> > +	 * asssociated instance for avoiding potential use-after-free, and
> > +	 * its pair is the memory barrier implied in sbitmap_get().
> which one ?

test_and_set_bit_lock() in __sbitmap_get_word().

> 
> > +	 */
> > +	smp_mb();
> 
> smp_mb_before_atomic should be enough.

Right, will change to it in V2.

Thanks,
Ming