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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org, Frank Rowand <frowand.list@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Segher Boessenkool <segher@kernel.crashing.org>
Subject: Re: [PATCH] of: Rework and simplify phandle cache to use a fixed size
Date: Thu, 12 Dec 2019 14:05:39 +0100	[thread overview]
Message-ID: <20191212130539.loxpr2hbfcodh4gz@linutronix.de> (raw)
In-Reply-To: <CAL_JsqKfV-4mx_uidUupQJT4qfq+y+qx1=S=Du-Qsaweh4CPUQ@mail.gmail.com>

On 2019-12-11 17:48:54 [-0600], Rob Herring wrote:
> > -       if (phandle_cache) {
> > -               if (phandle_cache[masked_handle] &&
> > -                   handle == phandle_cache[masked_handle]->phandle)
> > -                       np = phandle_cache[masked_handle];
> > -               if (np && of_node_check_flag(np, OF_DETACHED)) {
> > -                       WARN_ON(1); /* did not uncache np on node removal */
> > -                       of_node_put(np);
> > -                       phandle_cache[masked_handle] = NULL;
> > -                       np = NULL;
> > -               }
> > +       if (phandle_cache[handle_hash] &&
> > +           handle == phandle_cache[handle_hash]->phandle)
> > +               np = phandle_cache[handle_hash];
> > +       if (np && of_node_check_flag(np, OF_DETACHED)) {
> > +               WARN_ON(1); /* did not uncache np on node removal */
> 
> BTW, I don't think this check is even valid. If we failed to detach
> and remove the node from the cache, then we could be accessing np
> after freeing it.

this is kmalloc()ed memory which is always valid. If the memory is
already re-used then
	handle == phandle_cache[handle_hash]->phandle

will fail (the check, not the memory access itself). If the check
remains valid then you can hope for the OF_DETACHED flag to trigger the
warning.

> Rob

Sebastian

  reply	other threads:[~2019-12-12 13:05 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-11 23:23 [PATCH] of: Rework and simplify phandle cache to use a fixed size Rob Herring
2019-12-11 23:48 ` Rob Herring
2019-12-12 13:05   ` Sebastian Andrzej Siewior [this message]
2019-12-12 19:28     ` Rob Herring
2019-12-18  9:47       ` Sebastian Andrzej Siewior
2019-12-19 15:33     ` Frank Rowand
2019-12-19 15:31   ` Frank Rowand
2019-12-12 11:50 ` Frank Rowand
2019-12-19  3:38   ` Frank Rowand
2019-12-12 13:00 ` Sebastian Andrzej Siewior
2019-12-19 15:51 ` Frank Rowand
2020-01-07 10:22 ` Jon Hunter
2020-01-10 23:50   ` Rob Herring
2020-01-13 11:12     ` Jon Hunter
2020-04-14 15:00       ` Rob Herring
2020-04-14 19:43         ` Jon Hunter

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