From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id A14761A0BBF for ; Thu, 14 May 2015 12:53:10 +1000 (AEST) Message-ID: <1431571984.3625.91.camel@redhat.com> Subject: Re: [PATCH kernel v10 05/34] powerpc/iommu: Always release iommu_table in iommu_free_table() From: Alex Williamson To: Alexey Kardashevskiy Date: Wed, 13 May 2015 20:53:04 -0600 In-Reply-To: <555409B8.3060904@ozlabs.ru> References: <1431358763-24371-1-git-send-email-aik@ozlabs.ru> <1431358763-24371-6-git-send-email-aik@ozlabs.ru> <20150513053337.GA479@gwshan> <5552EF78.6020301@ozlabs.ru> <20150513145136.1a85f536@thh440s> <20150513232745.GA8158@gwshan> <555409B8.3060904@ozlabs.ru> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: Thomas Huth , Gavin Shan , linux-kernel@vger.kernel.org, Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Wei Yang , David Gibson List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2015-05-14 at 12:34 +1000, Alexey Kardashevskiy wrote: > On 05/14/2015 09:27 AM, Gavin Shan wrote: > > On Wed, May 13, 2015 at 02:51:36PM +0200, Thomas Huth wrote: > >> On Wed, 13 May 2015 16:30:16 +1000 > >> Alexey Kardashevskiy 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 > >>>> > >>>> Reviewed-by: Gavin Shan > >>>> > >>>>> --- > >>>>> 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. > >> > > > > If I understood your question correctly, "tbl->it_map" won't be checked > > when "tbl" is NULL because the connection ("||") for the two conditions. > > The code can be changed to something like below if Alexey want: > > > > if (!tbl) > > return; > > if (!tbl->itmap) > > kfree(tbl); > > To be precise ;) > > if (!tbl->itmap) { > kfree(tbl); > return; > } I hope that's not your solution, it clearly segfaults with a null pointer de-ref if !tbl, which is apparently a concern down this path.