Dear Arunprivin,
Am 16.03.22 um 07:49 schrieb Arunpravin Paneer Selvam:
On 15/03/22 9:14 pm, Paul Menzel wrote:
Am 15.03.22 um 16:42 schrieb Arunpravin:
On 15/03/22 2:35 pm, Paul Menzel wrote:
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.PaneerSelvam@xxxxxxx>
Please use your full name.
okay
You might also configure that in your email program.
yes
Not done yet though. ;-)
done in v2 :)
---
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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcgit.freedesktop.org%2Fdrm-tip%2Ftree%2F&data=04%7C01%7CArunpravin.PaneerSelvam%40amd.com%7C3610aafe216d421c715c08da069ac1d7%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637829559006306914%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=GM3iXiDQCx%2BM4pD1nmivRFRvkehwTNd2Jtd713cF51g%3D&reserved=0
drm-misc-next - https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcgit.freedesktop.org%2Fdrm%2Fdrm-misc%2Ftree%2F&data=04%7C01%7CArunpravin.PaneerSelvam%40amd.com%7C3610aafe216d421c715c08da069ac1d7%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637829559006306914%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=i7pvmDJu310XRX7h3cQ344j5RYHq7fBZ520l%2F%2Br1%2BQU%3D&reserved=0
Thank Outlook. Now everybody feels safe.
@@ -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);
no, this BUG_ON is not triggered for this bug
Please give more details.
there is a chance when there is no space to allocate, order value
decrements and reaches to 0 at one point, here we should exit the loop,
otherwise, further order value decrements to -1 and do..while loop
doesn't exit. Hence added a check to exit the loop if order value becomes 0.
Sorry, I do not see it. How can that be with order ≥ min_order and the
check `order-- == min_order`? Is min_order 0? Please explain that in the
next commit message.
please check v2, yes when min_order is 0, the above said situation may
occur.And, since the order is unsigned int, I think it will not trigger
the BUG_ON(order < min_order) when order becomes -1. Hence I think we
needed a check !order to exit the loop.
Thank you for clarifying this. I still do not understand it though. With
order = fls(pages) - 1;
min_order = ilog2(min_page_size) - ilog2(mm->chunk_size);
is zorder` always non-negative? Let’s assume it is. Also, can min_order
get “negative” (wraps around)?
I would add BUG_ON statements for these cases?
BUG_ON(fls(pages) - 1 < 1);
BUG_ON(ilog2(min_page_size) - ilog2(mm->chunk_size) < 1);
Assuming “negative” is not possible, your case can only happen if
`order` and `min_order` are 0, right? If `order` is greater than 0, and
`min_order` is 0, the first BUG_ON in the while loop would be hit. If
`order` is 0 and `min_order` is greater than 0, everything should work
as the condition in `if (order-- == min_order)` is going to be true
eventually.
Could you please analyze this more. The current patch looks more like
papering over something, or I am missing something.
Kind regards,
Paul
PS: The commit message summary of your v2 should also be updated.
