Hi Joerg,
Could you please review this patch ?
Thanks,
Oded
On 10/25/2014 10:16 PM, Oded Gabbay wrote:
Hi,
Could anyone please review this patch ?
Thanks,
Oded
On 18/10/14 00:43, Oded Gabbay wrote:
This patch makes use of the new delayed mmu release notifier feature in
mm code. This is necessary because on the one hand amd_iommu_unbind_pasid
must be called explicitly during the tear-down of a process, but on the
other hand, it could be called from a function (e.g. in amdkfd)
which is a call-back function for the mmu notifier release.
In such a case, amd_iommu_unbind_pasid must not free the pasid_state
object, as it is a member in the list of mmu release notifiers (and
freeing it in the middle of iterating the list will break the list).
Therefore, this patch delays the release of pasid_state to a later
call-back, which is called inside an srcu, and there we can freely
release the object.
The flow of function calls when a process is teared-down looks like this:
(This flow assumes that amdkfd is the client of amd_iommu_v2)
1. mmu release notifiers for the destroyed process are started to get called.
2. amd_iommu_v2 notifier gets called, and it calls a call-back
function (inv_ctx_cb). amdkfd, which implements this call-back function,
performs tear-down of the relevant queues per device per process.
3. Later, amdkfd's mmu notifier callback (kfd_process_notifier_release()) gets
called and releases more things that are related to the process.
In that function, amd_iommu_unbind_pasid() is explicitly called.
4. (current code) amd_iommu_unbind_pasid() frees the mmu notifier
object itself, which mustn't be freed while iterating over the list
of mmu notifiers.
4. (new code in this patch) amd_iommu_unbind_pasid() sets a delayed notifier,
using the delayed mmu release notifier feature (new in 3.17),
which does the actual release later, after the iteration over the list of
mmu notifiers is over.
Signed-off-by: Oded Gabbay <[email protected]>
---
drivers/iommu/amd_iommu_v2.c | 32 +++++++++++++++++++++++++++++---
1 file changed, 29 insertions(+), 3 deletions(-)
diff --git a/drivers/iommu/amd_iommu_v2.c b/drivers/iommu/amd_iommu_v2.c
index 5f578e8..1e83bdd 100644
--- a/drivers/iommu/amd_iommu_v2.c
+++ b/drivers/iommu/amd_iommu_v2.c
@@ -57,6 +57,9 @@ struct pasid_state {
spinlock_t lock; /* Protect pri_queues and
mmu_notifer_count */
wait_queue_head_t wq; /* To wait for count == 0 */
+
+ struct rcu_head rcu; /* Use for delayed freeing of
+ pasid_state structure */
};
struct device_state {
@@ -297,7 +300,6 @@ static void put_pasid_state_wait(struct pasid_state
*pasid_state)
schedule();
finish_wait(&pasid_state->wq, &wait);
- free_pasid_state(pasid_state);
}
static void unbind_pasid(struct pasid_state *pasid_state)
@@ -369,6 +371,8 @@ static void free_pasid_states(struct device_state
*dev_state)
put_pasid_state_wait(pasid_state); /* Reference taken in
amd_iommu_bind_pasid */
+ free_pasid_state(pasid_state);
+
/* Drop reference taken in amd_iommu_bind_pasid */
put_device_state(dev_state);
}
@@ -711,6 +715,17 @@ out:
}
EXPORT_SYMBOL(amd_iommu_bind_pasid);
+static void pasid_state_destroy_delayed(struct rcu_head *rcu)
+{
+ struct pasid_state *pasid_state;
+
+ pasid_state = container_of(rcu, struct pasid_state, rcu);
+
+ mmdrop(pasid_state->mm);
+
+ free_pasid_state(pasid_state);
+}
+
void amd_iommu_unbind_pasid(struct pci_dev *pdev, int pasid)
{
struct pasid_state *pasid_state;
@@ -743,13 +758,24 @@ void amd_iommu_unbind_pasid(struct pci_dev *pdev, int
pasid)
clear_pasid_state(dev_state, pasid_state->pasid);
/*
+ * Because we drop mm_count inside pasid_state_destroy_delayed
+ * and because the mmu_notifier_unregister function also drop
+ * mm_count we need to take an extra count here.
+ */
+ atomic_inc(&pasid_state->mm->mm_count);
+
+ /*
* Call mmu_notifier_unregister to drop our reference
* to pasid_state->mm
*/
- mmu_notifier_unregister(&pasid_state->mn, pasid_state->mm);
+ mmu_notifier_unregister_no_release(&pasid_state->mn, pasid_state->mm);
put_pasid_state_wait(pasid_state); /* Reference taken in
- amd_iommu_bind_pasid */
+ amd_iommu_pasid_bind */
+
+ mmu_notifier_call_srcu(&pasid_state->rcu,
+ &pasid_state_destroy_delayed);
+
out:
/* Drop reference taken in this function */
put_device_state(dev_state);
--
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