Re: [PATCH] drm/buddy: Fix alloc_range() error handling code

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]


On 08/02/2024 14:17, Matthew Auld wrote:
On 08/02/2024 13:47, Arunpravin Paneer Selvam wrote:
Hi Matthew,

On 2/8/2024 7:00 PM, Matthew Auld wrote:
On 07/02/2024 17:44, Arunpravin Paneer Selvam wrote:
Few users have observed display corruption when they boot
the machine to KDE Plasma or playing games. We have root
caused the problem that whenever alloc_range() couldn't
find the required memory blocks the function was returning
SUCCESS in some of the corner cases.

Can you please give an example here?

In the try hard contiguous allocation, for example the requested memory is 1024 pages, it might go and pick the highest and last block (of size 512 pages) in the freelist where there are no more space exist in the total address range. In this kind of corner case, alloc_range was returning success though the allocated size is less than the requested size. Hence in try_hard_contiguous_allocation, we will not proceed to the LHS allocation and we return only with the RHS allocation having only the 512 pages of allocation. This leads to display corruption in many use cases (I think mainly when requested for contiguous huge buffer)
mainly on APU platforms.

Ok, I guess other thing is doing:

lhs_offset = drm_buddy_block_offset(block) - lhs_size;

I presume it's possible for block_offset < lhs_size here, which might be funny?

I think would also be good to add some basic unit test here:

Test passes with your patch, and ofc fails without it.

Just the question of the lhs_offset above,
Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>


The right approach would be if the total allocated size
is less than the required size, the function should
return -ENOSPC.

Gitlab ticket link -
Fixes: 0a1844bf0b53 ("drm/buddy: Improve contiguous memory allocation")
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@xxxxxxx>
Tested-by: Mario Limonciello <mario.limonciello@xxxxxxx>
  drivers/gpu/drm/drm_buddy.c | 6 ++++++
  1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index f57e6d74fb0e..c1a99bf4dffd 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -539,6 +539,12 @@ static int __alloc_range(struct drm_buddy *mm,
      } while (1);
        list_splice_tail(&allocated, blocks);
+    if (total_allocated < size) {
+        err = -ENOSPC;
+        goto err_free;
+    }
      return 0;

[Index of Archives]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux