6.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: Daniel Marcovitch <dmarcovitch@xxxxxxxxxx>
[ Upstream commit 534103bcd52ca9c1fecbc70e717b4a538dc4ded8 ]
When unbinding pasid - a race condition exists vs outstanding page faults.
To prevent this, the pasid_state object contains a refcount.
* set to 1 on pasid bind
* incremented on each ppr notification start
* decremented on each ppr notification done
* decremented on pasid unbind
Since refcount_dec assumes that refcount will never reach 0:
the current implementation causes the following to be invoked on
pasid unbind:
REFCOUNT_WARN("decrement hit 0; leaking memory")
Fix this issue by changing refcount_dec to refcount_dec_and_test
to explicitly handle refcount=1.
Fixes: 8bc54824da4e ("iommu/amd: Convert from atomic_t to refcount_t on pasid_state->count")
Signed-off-by: Daniel Marcovitch <dmarcovitch@xxxxxxxxxx>
Signed-off-by: Vasant Hegde <vasant.hegde@xxxxxxx>
Link: https://lore.kernel.org/r/20230609105146.7773-2-vasant.hegde@xxxxxxx
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/iommu/amd/iommu_v2.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/iommu/amd/iommu_v2.c b/drivers/iommu/amd/iommu_v2.c
index 261352a232716..65d78d7e04408 100644
--- a/drivers/iommu/amd/iommu_v2.c
+++ b/drivers/iommu/amd/iommu_v2.c
@@ -262,8 +262,8 @@ static void put_pasid_state(struct pasid_state *pasid_state)
static void put_pasid_state_wait(struct pasid_state *pasid_state)
{
- refcount_dec(&pasid_state->count);
- wait_event(pasid_state->wq, !refcount_read(&pasid_state->count));
+ if (!refcount_dec_and_test(&pasid_state->count))
+ wait_event(pasid_state->wq, !refcount_read(&pasid_state->count));
free_pasid_state(pasid_state);
}
--
2.40.1
