linux-kernel - Re: [PATCH] Intel IOMMU: get_domain_for_dev() leaks a bit of mem if dmar_find_matched_drhd

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Date:	Thu, 10 Feb 2011 19:17:49 +0100 (CET)
From:	Jesper Juhl <jj@...osbits.net>
To:	Alex Williamson <alex.williamson@...hat.com>
cc:	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	iommu@...ts.linux-foundation.org,
	Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
	Shaohua Li <shaohua.li@...el.com>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH] Intel IOMMU: get_domain_for_dev() leaks a bit of mem if
 dmar_find_matched_drhd_unit() fails.

On Thu, 10 Feb 2011, Alex Williamson wrote:

> On Sun, 2011-02-06 at 21:11 +0100, Jesper Juhl wrote:
> > I believe that there's a small memory leak in 
> > drivers/pci/intel-iommu.c:get_domain_for_dev().
> > 
> > If the call to alloc_domain() succeeds but the subsequent call to 
> > dmar_find_matched_drhd_unit() fails, then the current code will return 
> > NULL without calling domain_exit(domain) which will leak the memory that 
> > alloc_domain() allocated.
> > 
> > The easy fix for that is to simply move the call to alloc_domain() below 
> > the call to dmar_find_matched_drhd_unit() since the latter does not depend 
> > on the former.
> > 
> > I also made the change of moving the assignment to local variable 'iommu' 
> > below both calls since there is no point in doing that work if either of 
> > those those calls fail.
> > 
> > I also changed the 'return NULL' in the dmar_find_matched_drhd_unit() 
> > failure case to a 'goto error' since I figured that if rechecking 
> > 'find_domain(pdev)' makes sense after a alloc_domain() failure then it 
> > would also make sense after a dmar_find_matched_drhd_unit() failure.
> 
> I don't think this change buys us anything.  The goto error here seems
> to be a hope that another cpu may have beat us and succeeded at
> something we failed.  In the case of matching the pci device to a drhd,
> this should be deterministic (unless maybe we're racing a hot added
> drhd).  The rest seems fine to me.  Thanks,
> 
> Alex
> 

Ok. Updated patch below that leaves out the 'goto error' bit for 
dmar_find_matched_drhd_unit() failures.



There is a small memory leak in 
drivers/pci/intel-iommu.c:get_domain_for_dev().

If the call to alloc_domain() succeeds but the subsequent call to 
dmar_find_matched_drhd_unit() fails, then the current code will return 
NULL without calling domain_exit(domain) which will leak the memory that 
alloc_domain() allocated.

The easy fix for that is to simply move the call to alloc_domain() below 
the call to dmar_find_matched_drhd_unit() since the latter does not depend 
on the former.

Signed-off-by: Jesper Juhl <jj@...osbits.net>
---
 intel-iommu.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
index 4789f8e..3cfb021 100644
--- a/drivers/pci/intel-iommu.c
+++ b/drivers/pci/intel-iommu.c
@@ -1820,10 +1820,6 @@ static struct dmar_domain *get_domain_for_dev(struct pci_dev *pdev, int gaw)
 		}
 	}
 
-	domain = alloc_domain();
-	if (!domain)
-		goto error;
-
 	/* Allocate new domain for the device */
 	drhd = dmar_find_matched_drhd_unit(pdev);
 	if (!drhd) {
@@ -1831,8 +1827,11 @@ static struct dmar_domain *get_domain_for_dev(struct pci_dev *pdev, int gaw)
 			pci_name(pdev));
 		return NULL;
 	}
-	iommu = drhd->iommu;
+	domain = alloc_domain();
+	if (!domain)
+		goto error;
 
+	iommu = drhd->iommu;
 	ret = iommu_attach_domain(domain, iommu);
 	if (ret) {
 		domain_exit(domain);


-- 
Jesper Juhl <jj@...osbits.net>            http://www.chaosbits.net/
Plain text mails only, please.
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html

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