Am 30.03.23 um 12:53 schrieb Jani Nikula:
On Wed, 29 Mar 2023, David Gow <davidgow@xxxxxxxxxx> wrote:
The drm buddy allocator tests were broken on 32-bit systems, as
rounddown_pow_of_two() takes a long, and the buddy allocator handles
64-bit sizes even on 32-bit systems.
This can be reproduced with the drm_buddy_allocator KUnit tests on i386:
./tools/testing/kunit/kunit.py run --arch i386 \
--kunitconfig ./drivers/gpu/drm/tests drm_buddy
(It results in kernel BUG_ON() when too many blocks are created, due to
the block size being too small.)
This was independently uncovered (and fixed) by Luís Mendes, whose patch
added a new u64 variant of rounddown_pow_of_two(). This version instead
recalculates the size based on the order.
Reported-by: Luís Mendes <luis.p.mendes@xxxxxxxxx>
Link: https://lore.kernel.org/lkml/CAEzXK1oghXAB_KpKpm=-CviDQbNaH0qfgYTSSjZgvvyj4U78AA@xxxxxxxxxxxxxx/T/
Signed-off-by: David Gow <davidgow@xxxxxxxxxx>
---
drivers/gpu/drm/drm_buddy.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index 3d1f50f481cf..7098f125b54a 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -146,8 +146,8 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
unsigned int order;
u64 root_size;
- root_size = rounddown_pow_of_two(size);
- order = ilog2(root_size) - ilog2(chunk_size);
+ order = ilog2(size) - ilog2(chunk_size);
+ root_size = chunk_size << order;
Just noticed near the beginning of the function there's also:
if (!is_power_of_2(chunk_size))
return -EINVAL;
which is also wrong for 32-bit.
Yeah, but that isn't vital. We just use u64 for the chunk_size for
consistency.
In reality I wouldn't except more than 256K here.
Regards,
Christian.
BR,
Jani.
root = drm_block_alloc(mm, NULL, order, offset);
if (!root)
