Re: [resend PATCH] drm/ttm: Fix a deadlock if the target BO is not idle during swap

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Am 07.09.21 um 11:05 schrieb Daniel Vetter:
On Tue, Sep 07, 2021 at 08:22:20AM +0200, Christian König wrote:
Added a Fixes tag and pushed this to drm-misc-fixes.
We're in the merge window, this should have been drm-misc-next-fixes. I'll
poke misc maintainers so it's not lost.

Hui? It's a fix for a problem in stable and not in drm-misc-next.

Christian.

-Daniel

It will take a while until it cycles back into the development branches, so
feel free to push some version to amd-staging-drm-next as well. Just ping
Alex when you do this.

Thanks,
Christian.

Am 07.09.21 um 06:08 schrieb xinhui pan:
The ret value might be -EBUSY, caller will think lru lock is still
locked but actually NOT. So return -ENOSPC instead. Otherwise we hit
list corruption.

ttm_bo_cleanup_refs might fail too if BO is not idle. If we return 0,
caller(ttm_tt_populate -> ttm_global_swapout ->ttm_device_swapout) will
be stuck as we actually did not free any BO memory. This usually happens
when the fence is not signaled for a long time.

Signed-off-by: xinhui pan <xinhui.pan@xxxxxxx>
Reviewed-by: Christian König <christian.koenig@xxxxxxx>
---
   drivers/gpu/drm/ttm/ttm_bo.c | 6 +++---
   1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 8d7fd65ccced..23f906941ac9 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -1152,9 +1152,9 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
   	}
   	if (bo->deleted) {
-		ttm_bo_cleanup_refs(bo, false, false, locked);
+		ret = ttm_bo_cleanup_refs(bo, false, false, locked);
   		ttm_bo_put(bo);
-		return 0;
+		return ret == -EBUSY ? -ENOSPC : ret;
   	}
   	ttm_bo_del_from_lru(bo);
@@ -1208,7 +1208,7 @@ int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,
   	if (locked)
   		dma_resv_unlock(bo->base.resv);
   	ttm_bo_put(bo);
-	return ret;
+	return ret == -EBUSY ? -ENOSPC : ret;
   }
   void ttm_bo_tt_destroy(struct ttm_buffer_object *bo)




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