Am 14.02.2017 um 10:18 schrieb Nicolai Hähnle:
From: Nicolai Hähnle <nicolai.haehnle@xxxxxxx>
Fixes a potential race condition in amdgpu that looks as follows:
Task 1: attempt ttm_bo_init, but ttm_bo_validate fails
Task 1: add BO to global list anyway
Task 2: grabs hold of the BO, waits on its reservation lock
Task 1: releases its reference of the BO; never gives up the
reservation lock
The patch "drm/amdgpu: fix a potential deadlock in
amdgpu_bo_create_restricted()" attempts to fix that by releasing
the reservation lock in amdgpu code; unfortunately, it introduces
a use-after-free when this race _doesn't_ happen.
This patch should fix the race properly by never adding the BO
to the global list in the first place.
Cc: Samuel Pitoiset <samuel.pitoiset@xxxxxxxxx>
Cc: zhoucm1 <david1.zhou@xxxxxxx>
Signed-off-by: Nicolai Hähnle <nicolai.haehnle@xxxxxxx>
NAK, that is actually not correct either.
The previous implementation doesn't have an use after free, but actually
a memory leak.
I completely agree that adding the BO to the LRU in case of an error is
incorrect, but ttm_bo_add_to_lru() will add some references to the BO.
So the following ttm_bo_unref() will just drop the initial reference.
Let's clean up this mess by moving the freeing of the BO in case of an
error to the caller.
Regards,
Christian.
---
drivers/gpu/drm/ttm/ttm_bo.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 239a957..76bee42 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -1215,18 +1215,20 @@ int ttm_bo_init(struct ttm_bo_device *bdev,
if (likely(!ret))
ret = ttm_bo_validate(bo, placement, interruptible, false);
- if (!resv) {
+ if (!resv)
ttm_bo_unreserve(bo);
- } else if (!(bo->mem.placement & TTM_PL_FLAG_NO_EVICT)) {
+ if (unlikely(ret)) {
+ ttm_bo_unref(&bo);
+ return ret;
+ }
+
+ if (resv && !(bo->mem.placement & TTM_PL_FLAG_NO_EVICT)) {
spin_lock(&bo->glob->lru_lock);
ttm_bo_add_to_lru(bo);
spin_unlock(&bo->glob->lru_lock);
}
- if (unlikely(ret))
- ttm_bo_unref(&bo);
-
return ret;
}
EXPORT_SYMBOL(ttm_bo_init);
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