linux-kernel - Re: [PATCH kernel v10 05/34] powerpc/iommu: Always release iommu_table in iommu_free

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Message-ID: <20150513145136.1a85f536@thh440s>
Date:	Wed, 13 May 2015 14:51:36 +0200
From:	Thomas Huth <thuth@...hat.com>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	Wei Yang <weiyang@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Alex Williamson <alex.williamson@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH kernel v10 05/34] powerpc/iommu: Always release
 iommu_table in iommu_free_table()

On Wed, 13 May 2015 16:30:16 +1000
Alexey Kardashevskiy <aik@...abs.ru> wrote:

> On 05/13/2015 03:33 PM, Gavin Shan wrote:
> > On Tue, May 12, 2015 at 01:38:54AM +1000, Alexey Kardashevskiy wrote:
> >> At the moment iommu_free_table() only releases memory if
> >> the table was initialized for the platform code use, i.e. it had
> >> it_map initialized (which purpose is to track DMA memory space use).
> >>
> >> With dynamic DMA windows, we will need to be able to release
> >> iommu_table even if it was used for VFIO in which case it_map is NULL
> >> so does the patch.
> >>
> >> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
> >
> > Reviewed-by: Gavin Shan <gwshan@...ux.vnet.ibm.com>
> >
> >> ---
> >> arch/powerpc/kernel/iommu.c | 3 +--
> >> 1 file changed, 1 insertion(+), 2 deletions(-)
> >>
> >> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> >> index 3d47eb3..2c02d4c 100644
> >> --- a/arch/powerpc/kernel/iommu.c
> >> +++ b/arch/powerpc/kernel/iommu.c
> >> @@ -714,8 +714,7 @@ void iommu_free_table(struct iommu_table *tbl, const char *node_name)
> >> 	unsigned int order;
> >>
> >> 	if (!tbl || !tbl->it_map) {
> >> -		printk(KERN_ERR "%s: expected TCE map for %s\n", __func__,
> >> -				node_name);
> >> +		kfree(tbl);
> >
> > I'm not sure if the "tbl" needs to be checked against NULL as kfree() already
> > has the check. But it looks a bit strange to free NULL "tbl" from the code
> > itself.
> 
> Yeah, looks a bit weird, agree, I'll change but in general kfree/vfree/... 
> - they all check the passed pointer for NULL.

But if tbl is NULL, the tbl->it_map check will fail, won't it? So in
this case, I think you have to keep it.

 Thomas
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