linux-kernel - [PATCH 3.2 100/149] powerpc/iommu: Use GFP_KERNEL instead of GFP_ATOMIC in iommu_init

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Message-ID: <lsq.1382345188.579162159@decadent.org.uk>
Date:	Mon, 21 Oct 2013 09:46:28 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Nishanth Aravamudan" <nacc@...ux.vnet.ibm.com>,
	"Nishanth Aravamudan" <nacc@...ibm.com>,
	"Benjamin Herrenschmidt" <benh@...nel.crashing.org>
Subject: [PATCH 3.2 100/149] powerpc/iommu: Use GFP_KERNEL instead of
 GFP_ATOMIC in iommu_init_table()

3.2.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>

commit 1cf389df090194a0976dc867b7fffe99d9d490cb upstream.

Under heavy (DLPAR?) stress, we tripped this panic() in
arch/powerpc/kernel/iommu.c::iommu_init_table():

	page = alloc_pages_node(nid, GFP_ATOMIC, get_order(sz));
	if (!page)
		panic("iommu_init_table: Can't allocate %ld bytes\n", sz);

Before the panic() we got a page allocation failure for an order-2
allocation. There appears to be memory free, but perhaps not in the
ATOMIC context. I looked through all the call-sites of
iommu_init_table() and didn't see any obvious reason to need an ATOMIC
allocation. Most call-sites in fact have an explicit GFP_KERNEL
allocation shortly before the call to iommu_init_table(), indicating we
are not in an atomic context. There is some indirection for some paths,
but I didn't see any locks indicating that GFP_KERNEL is inappropriate.

With this change under the same conditions, we have not been able to
reproduce the panic.

Signed-off-by: Nishanth Aravamudan <nacc@...ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/powerpc/kernel/iommu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/kernel/iommu.c
+++ b/arch/powerpc/kernel/iommu.c
@@ -495,7 +495,7 @@ struct iommu_table *iommu_init_table(str
 	/* number of bytes needed for the bitmap */
 	sz = (tbl->it_size + 7) >> 3;

-	page = alloc_pages_node(nid, GFP_ATOMIC, get_order(sz));
+	page = alloc_pages_node(nid, GFP_KERNEL, get_order(sz));
 	if (!page)
 		panic("iommu_init_table: Can't allocate %ld bytes\n", sz);
 	tbl->it_map = page_address(page);

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