Re: [Intel-gfx] [PATCH] drm: Fix a infinite loop condition when order becomes 0

[Paul Menzel]

Dear Arunpravin,


Am 15.03.22 um 10:01 schrieb Arunpravin:

On 15/03/22 1:49 pm, Paul Menzel wrote:

Am 14.03.22 um 20:40 schrieb Arunpravin:

handle a situation in the condition order-- == min_order,
when order = 0, leading to order = -1, it now won't exit
the loop. To avoid this problem, added a order check in
the same condition, (i.e) when order is 0, we return
-ENOSPC

Signed-off-by: Arunpravin <arunpravin.paneersel...@amd.com>

Please use your full name.

okay

You might also configure that in your email program.

---
   drivers/gpu/drm/drm_buddy.c | 2 +-
   1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index 72f52f293249..5ab66aaf2bbd 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c

In what tree is that file?

drm-tip - https://cgit.freedesktop.org/drm-tip/tree/
drm-misc-next - https://cgit.freedesktop.org/drm/drm-misc/tree/

@@ -685,7 +685,7 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
                        if (!IS_ERR(block))
                                break;

- if (order-- == min_order) {

+                       if (!order || order-- == min_order) {
                                err = -ENOSPC;
                                goto err_free;
                        }

Thank you for the hint. So the whole function is:

        do {
                order = min(order, (unsigned int)fls(pages) - 1);
                BUG_ON(order > mm->max_order);
                BUG_ON(order < min_order);

                do {
                        if (flags & DRM_BUDDY_RANGE_ALLOCATION)
                                /* Allocate traversing within the range */
                                block = alloc_range_bias(mm, start, end, order);
                        else
                                /* Allocate from freelist */
                                block = alloc_from_freelist(mm, order, flags);

                        if (!IS_ERR(block))
                                break;

                        if (order-- == min_order) {
                                err = -ENOSPC;
                                goto err_free;
                        }
                } while (1);

                mark_allocated(block);
                mm->avail -= drm_buddy_block_size(mm, block);
                kmemleak_update_trace(block);
                list_add_tail(&block->link, &allocated);

                pages -= BIT(order);

                if (!pages)
                        break;
        } while (1);

Was the BUG_ON triggered for your case?

        BUG_ON(order < min_order);

Please give more details.


Kind regards,

Paul