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iommu/amd: Fix accounting of device_state 

This patch fixes a bug in the accounting of the
device_state.  In the current code, the device_state was put
(decremented) too many times, which sometimes lead to the
driver getting stuck permanently in put_device_state_wait().
That happen because the device_state->count would go below
zero, which is never supposed to happen.

The root cause is that the device_state was decremented in
put_pasid_state() and put_pasid_state_wait() but also in all
the functions that call those functions. Therefore, the
device_state was decremented twice in each of these code
paths.

The fix is to decouple the device_state accounting from the
pasid_state accounting - remove the call to
put_device_state() from the put_pasid_state() and the
put_pasid_state_wait())

Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
This commit is contained in:
Oded Gabbay 2014-11-10 12:21:39 +02:00 committed by Joerg Roedel
parent 206c5f60a3
commit 1c51099a42
1 changed files with 2 additions and 6 deletions
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8
drivers/iommu/amd_iommu_v2.c
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@ -279,10 +279,8 @@ static void free_pasid_state(struct pasid_state *pasid_state)
static void put_pasid_state(struct pasid_state *pasid_state)
{
if (atomic_dec_and_test(&pasid_state->count)) {
put_device_state(pasid_state->device_state);
if (atomic_dec_and_test(&pasid_state->count))
wake_up(&pasid_state->wq);
}
}
static void put_pasid_state_wait(struct pasid_state *pasid_state)
@ -291,9 +289,7 @@ static void put_pasid_state_wait(struct pasid_state *pasid_state)
prepare_to_wait(&pasid_state->wq, &wait, TASK_UNINTERRUPTIBLE);
if (atomic_dec_and_test(&pasid_state->count))
put_device_state(pasid_state->device_state);
else
if (!atomic_dec_and_test(&pasid_state->count))
schedule();
finish_wait(&pasid_state->wq, &wait);