On 01/05/2018 11:36 AM, Chris Wilson wrote:
Quoting Laura Abbott (2018-01-05 19:14:08)
syzbot reported a warning from Ion:
WARNING: CPU: 1 PID: 3485 at mm/page_alloc.c:3926
...
__alloc_pages_nodemask+0x9fb/0xd80 mm/page_alloc.c:4252
alloc_pages_current+0xb6/0x1e0 mm/mempolicy.c:2036
alloc_pages include/linux/gfp.h:492 [inline]
ion_system_contig_heap_allocate+0x40/0x2c0
drivers/staging/android/ion/ion_system_heap.c:374
ion_buffer_create drivers/staging/android/ion/ion.c:93 [inline]
ion_alloc+0x2c1/0x9e0 drivers/staging/android/ion/ion.c:420
ion_ioctl+0x26d/0x380 drivers/staging/android/ion/ion-ioctl.c:84
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
This is a warning about attempting to allocate order > MAX_ORDER. This
is coming from a userspace Ion allocation request. Since userspace is
free to request however much memory it wants (and the kernel is free to
deny its allocation), silence the allocation attempt with __GFP_NOWARN
in case it fails.
Reported-by: syzbot+76e7efc4748495855a4d@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
---
drivers/staging/android/ion/ion_system_heap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c
index 71c4228f8238..bc19cdd30637 100644
--- a/drivers/staging/android/ion/ion_system_heap.c
+++ b/drivers/staging/android/ion/ion_system_heap.c
@@ -362,7 +362,7 @@ static int ion_system_contig_heap_allocate(struct ion_heap *heap,
unsigned long i;
int ret;
- page = alloc_pages(low_order_gfp_flags, order);
+ page = alloc_pages(low_order_gfp_flags | __GFP_NOWARN, order);
There's both high_order_gfp and low_order_gfp. The former includes
NOWARN and NORETRY.
Interesting, ion_system_heap_create_pools() tries to mix low_order and
high_order, but it only ever uses high_order flags. (orders[0] == 8
forcing a permanent switch from low_order_gfp to high_order_gfp).
Good find, that got lost in a refactor back in 4.9.
There's no good reason for low_order_gfp, high_order_gfp to be static
rewritable variables.
For this instance, I would go farther and suggest you may want
__GFP_RETRY_MAYFAIL | __GFP_NOWARN to prevent userspace from triggering
the lowmemkiller/oomkiller here.
(I would kill low_order_gfp_flags / high_order_gfp_flags and avoid the
obfuscation.)
-Chris
Yeah, I think this all needs some refactoring. The high_order/low_order
flags were originally for the system heap to allocate pages for the
page pool and I don't think they should be reused for the contig heap.
I'll see about doing a refactor.
Thanks for the review!
Laura
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