[PATCH] vmalloc: fix __GFP_HIGHMEM usage for vmalloc_32 on 32b systems

[Michal Hocko]

Kai Heng Feng has noticed that BUG_ON(PageHighMem(pg)) triggers in
drivers/media/common/saa7146/saa7146_core.c since 19809c2da28a ("mm,
vmalloc: use __GFP_HIGHMEM implicitlyâ). saa7146_vmalloc_build_pgtable
uses vmalloc_32 and it is reasonable to expect that the resulting page
is not in highmem. The above commit aimed to add __GFP_HIGHMEM only
for those requests which do not specify any zone modifier gfp flag.
vmalloc_32 relies on GFP_VMALLOC32 which should do the right thing.
Except it has been missed that GFP_VMALLOC32 is an alias for GFP_KERNEL
on 32b architectures. Thanks to Matthew to notice this.

Fix the problem by unconditionally setting GFP_DMA32 in GFP_VMALLOC32
for !64b arches (as a bailout). This should do the right thing and use
ZONE_NORMAL which should be always below 4G on 32b systems.

Debugged-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Reported-by: Kai Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
Fixes: 19809c2da28a ("mm, vmalloc: use __GFP_HIGHMEM implicitlyâ)
Cc: stable
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 mm/vmalloc.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 673942094328..1d147078c469 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -1947,7 +1947,11 @@ void *vmalloc_exec(unsigned long size)
 #elif defined(CONFIG_64BIT) && defined(CONFIG_ZONE_DMA)
 #define GFP_VMALLOC32 GFP_DMA | GFP_KERNEL
 #else
-#define GFP_VMALLOC32 GFP_KERNEL
+/*
+ * 64b systems should always have either DMA or DMA32 zones. For others
+ * GFP_DMA32 should do the right thing and use the normal zone.
+ */
+#define GFP_VMALLOC32 GFP_DMA32 | GFP_KERNEL
 #endif
 
 /**
-- 
2.15.1

-- 
Michal Hocko
SUSE Labs