6.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: Daniel Marcovitch dmarcovitch@nvidia.com
[ 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@nvidia.com Signed-off-by: Vasant Hegde vasant.hegde@amd.com Link: https://lore.kernel.org/r/20230609105146.7773-2-vasant.hegde@amd.com Signed-off-by: Joerg Roedel jroedel@suse.de Signed-off-by: Sasha Levin sashal@kernel.org --- 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); }