linux-kernel - Re: [PATCH] mm: dmapool: Check the dma pool name

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Date:   Thu, 31 May 2018 10:34:44 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] mm: dmapool: Check the dma pool name

On 30 May 2018 at 23:41, Matthew Wilcox <willy@...radead.org> wrote:
> On Wed, May 30, 2018 at 08:13:27AM -0700, Matthew Wilcox wrote:
>> On Wed, May 30, 2018 at 08:14:09PM +0800, Baolin Wang wrote:
>> > On 30 May 2018 at 20:01, Matthew Wilcox <willy@...radead.org> wrote:
>> > > On Wed, May 30, 2018 at 07:28:43PM +0800, Baolin Wang wrote:
>> > >> It will be crash if we pass one NULL name when creating one dma pool,
>> > >> so we should check the passing name when copy it to dma pool.
>> > >
>> > > NAK.  Crashing is the appropriate thing to do.  Fix the caller to not
>> > > pass NULL.
>> > >
>> > > If you permit NULL to be passed then you're inviting crashes or just
>> > > bad reporting later when pool->name is printed.
>> >
>> > I think it just prints one NULL pool name. Sometimes the device
>> > doesn't care the dma pool names, so I think we can make code more
>> > solid to valid the passing parameters like other code does.
>> > Or can we add check to return NULL when the passing name is NULL
>> > instead of crashing the kernel? Thanks.
>>
>> No.  Fix your driver.
>
> Let me elaborate on this.  Kernel code is supposed to be "reasonable".
> That means we don't check every argument to every function for sanity,
> unless it's going to cause trouble later.  Crashing immediately with
> a bogus argument is fine; you can see the problem and fix it immediately.
> Returning NULL with a bad argument is actually worse; you won't know why
> the function returned NULL (maybe we're out of memory?) and you'll have
> a more complex debugging experience.
>
> Sometimes it makes sense to accept a NULL pointer and do something
> reasonable, like kfree().  In this case, we can eliminate checks in all
> the callers.  But we don't, in general, put sanity checks on arguments
> without a good reason.
>
> Your reasons aren't good.  "The driver doesn't care" -- well, just pass
> the driver's name, then.

Thanks for your explanation. OK, force the driver to pass a pool name.
Sorry for noises.

-- 
Baolin.wang
Best Regards