Re: [PATCH V2] drm/amdgpu: Fix incorrect return value

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Well multiple things to consider here.

This is clearly not called from the interrupt, otherwise locking a mutex would be illegal. So question is who is calling this? And can the function be called from different threads at the same time?

As far as I can see you don't take that into account in the patch.

When there is some kind of single threaded worker handling the RAS errors instead then I strongly suggest to solve this issue in the worker.

As far as I can see hacking around a broken caller by inserting amdgpu_vram_mgr_query_page_status() inside amdgpu_vram_mgr_reserve_range() is an absolutely no-go. That is really bad coding style.

What could be is that the VRAM manager needs to be able to provide atomic uniqueness for the reserved addresses, e.g. that amdgpu_vram_mgr_reserve_range() can be called multiple times with same address from multiple threads, but then we would need a different data structure than a linked list which is protected by a mutex.


Am 15.04.24 um 06:04 schrieb Chai, Thomas:
[AMD Official Use Only - General]

Hi Christian:
    If an ecc error occurs at an address, HW will generate an interrupt to SW to retire all pages located in the same physical row as the error address based on the physical characteristics of the memory device.
    Therefore, if other pages located on the same physical row as the error address also occur ecc errors later, HW will also generate multiple interrupts to SW to retire these same pages again, so that amdgpu_vram_mgr_reserve_range will be called multiple times to reserve the same pages.

     I think it's more appropriate to do the status check inside the function. If the function entry is not checked, people who are not familiar with this part of the code can easily make mistakes when calling the function.

Best Regards,

-----Original Message-----
From: Christian König <ckoenig.leichtzumerken@xxxxxxxxx>
Sent: Friday, April 12, 2024 5:24 PM
To: Chai, Thomas <YiPeng.Chai@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx
Cc: Chai, Thomas <YiPeng.Chai@xxxxxxx>; Zhang, Hawking <Hawking.Zhang@xxxxxxx>; Zhou1, Tao <Tao.Zhou1@xxxxxxx>; Li, Candice <Candice.Li@xxxxxxx>; Wang, Yang(Kevin) <KevinYang.Wang@xxxxxxx>; Yang, Stanley <Stanley.Yang@xxxxxxx>
Subject: Re: [PATCH V2] drm/amdgpu: Fix incorrect return value

Am 12.04.24 um 10:55 schrieb YiPeng Chai:
    After calling amdgpu_vram_mgr_reserve_range multiple times with the
same address, calling amdgpu_vram_mgr_query_page_status will always
return -EBUSY.
    From the second call to amdgpu_vram_mgr_reserve_range, the same
address will be added to the reservations_pending list again and is
never moved to the reserved_pages list because the address had been
Well just to make it clear that approach is a NAK until my concerns are solved.


    First add the address status check before calling
amdgpu_vram_mgr_do_reserve, if the address is already reserved, do
nothing; If the address is already in the reservations_pending list,
directly reserve memory; only add new nodes for the addresses that are
not in the reserved_pages list and reservations_pending list.

   Avoid repeated locking/unlocking.

Signed-off-by: YiPeng Chai <YiPeng.Chai@xxxxxxx>
   drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c | 25 +++++++++++++-------
   1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
index 1e36c428d254..a636d3f650b1 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vram_mgr.c
@@ -317,7 +317,6 @@ static void amdgpu_vram_mgr_do_reserve(struct
ttm_resource_manager *man)

               dev_dbg(adev->dev, "Reservation 0x%llx - %lld, Succeeded\n",
                       rsv->start, rsv->size);
               vis_usage = amdgpu_vram_mgr_vis_size(adev, block);
               atomic64_add(vis_usage, &mgr->vis_usage);
@@ -340,19 +339,27 @@ int amdgpu_vram_mgr_reserve_range(struct amdgpu_vram_mgr *mgr,
                                 uint64_t start, uint64_t size)
       struct amdgpu_vram_reservation *rsv;
+     int ret = 0;

-     rsv = kzalloc(sizeof(*rsv), GFP_KERNEL);
-     if (!rsv)
-             return -ENOMEM;
+     ret = amdgpu_vram_mgr_query_page_status(mgr, start);
+     if (!ret)
+             return 0;

-     INIT_LIST_HEAD(&rsv->allocated);
-     INIT_LIST_HEAD(&rsv->blocks);
+     if (ret == -ENOENT) {
+             rsv = kzalloc(sizeof(*rsv), GFP_KERNEL);
+             if (!rsv)
+                     return -ENOMEM;

-     rsv->start = start;
-     rsv->size = size;
+             INIT_LIST_HEAD(&rsv->allocated);
+             INIT_LIST_HEAD(&rsv->blocks);
+             rsv->start = start;
+             rsv->size = size;
+     }

-     list_add_tail(&rsv->blocks, &mgr->reservations_pending);
+     if (ret == -ENOENT)
+             list_add_tail(&rsv->blocks, &mgr->reservations_pending);

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