linux-kernel - Re: [PATCH] Avoid null-pointer access in w1/slaves/w1

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Date:	Wed, 18 Mar 2015 18:18:53 +0300
From:	Evgeniy Polyakov <zbr@...emap.net>
To:	David Fries <david@...es.net>
Cc:	Thorsten Bschorr <thorsten@...horr.de>,
	Jonathan ALIBERT <jonathan.alibert@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Avoid null-pointer access in w1/slaves/w1_therm

Hi

18.03.2015, 07:20, "David Fries" <david@...es.net>:
>  static void w1_therm_remove_slave(struct w1_slave *sl)
>  {
> + int refcnt = atomic_sub_return(1, THERM_REFCNT(sl->family_data));
> + while(refcnt) {
> + msleep(1000);
> + refcnt = atomic_read(THERM_REFCNT(sl->family_data));
> + }
>          kfree(sl->family_data);
>          sl->family_data = NULL;
>  }

Can we replace this whole atomic manipulations with kref_t and free family data in the place
which actually drops reference counter to zero?

I.e. we return from remove_slave() function potentially leaving family data floating around, it will be freed
when the last user drops the reference. There is still a race between increasing reference when starting
reading and removing slave device, i.e. one starts reading, while attached slave device is being removed,
but that's a different problem.
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