From: Xi Wang <xi.wang@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: fix NULL checking in dma_pool_create()
Date: Tue, 06 Nov 2012 15:48:26 -0500 [thread overview]
Message-ID: <5099779A.8050009@gmail.com> (raw)
In-Reply-To: <20121105132651.f52549b6.akpm@linux-foundation.org>
On 11/5/12 4:26 PM, Andrew Morton wrote:
>
> OK, so it seems that those drivers have never been tested on a
> CONFIG_NUMA kernel. whee.
>
> So we have a large amount of code here which ostensibly supports
> dev==NULL but which has not been well tested. Take a look at
> dma_alloc_coherent(), dma_free_coherent() - are they safe? Unobvious.
It's probably ok to call dma_alloc_coherent()/dma_free_coherent() with a
NULL dev. Quite a few drivers do that.
> dmam_pool_destroy() will clearly cause an oops:
>
> devres_destroy()
> ->devres_remove()
> ->spin_lock_irqsave(&dev->devres_lock, flags);
Not sure if I missed anything, but I haven't found any use of
dmam_pool_destroy() in the tree..
> I'm thinking we should disallow dev==NULL. We have a lot of code in
> mm/dmapool.c which _attempts_ to support this case, but is largely
> untested and obviously isn't working. I don't think it's a good idea
> to try to fix up and then support this case on behalf of a handful of
> scruffy drivers. It would be better to fix the drivers, then simplify
> the core code. drivers/usb/gadget/amd5536udc.c can probably use
> dev->gadget.dev and drivers/net/wan/ixp4xx_hss.c can probably use
> port->netdev->dev, etc.
After more search I've still only found 4 files that invoke
dma_pool_create() with a NULL dev.
arch/arm/mach-s3c64xx/dma.c
drivers/usb/gadget/amd5536udc.c
drivers/net/wan/ixp4xx_hss.c
drivers/net/ethernet/xscale/ixp4xx_eth.c
So, yeah, we could fix those drivers instead, such as adding
"WARN_ON_ONCE(dev == NULL)" as you suggested.
- xi
next prev parent reply other threads:[~2012-11-06 20:48 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-05 6:46 [PATCH] mm: fix NULL checking in dma_pool_create() Xi Wang
2012-11-05 20:37 ` Andrew Morton
2012-11-05 20:50 ` Xi Wang
2012-11-05 21:26 ` Andrew Morton
2012-11-06 20:48 ` Xi Wang [this message]
2012-11-13 21:39 ` [PATCH v2] mm: fix null dev " Xi Wang
2012-11-13 23:01 ` David Rientjes
2012-11-14 0:47 ` Andrew Morton
2012-11-14 0:58 ` Andrew Morton
2012-11-14 5:50 ` Xi Wang
2012-11-14 14:17 ` Felipe Balbi
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