linux-kernel - [PATCH v2] iommu/amd: Use wait_event in put_pasid_state

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Message-ID: <20150205114020.GQ3702@8bytes.org>
Date:	Thu, 5 Feb 2015 12:40:20 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	iommu@...ts.linux-foundation.org,
	Benjamin LaHaise <bcrl@...ck.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>, linux-aio@...ck.org,
	linux-kernel@...r.kernel.org, Oded Gabbay <oded.gabbay@....com>,
	jroedel@...e.de
Subject: [PATCH v2] iommu/amd: Use wait_event in put_pasid_state_wait

On Wed, Feb 04, 2015 at 05:34:50PM +0100, Peter Zijlstra wrote:
> You just lost your atomic_dec.

So this should be the correct version then.

>From 2a52250e542d8964c8285a37b71fe838a44c05c4 Mon Sep 17 00:00:00 2001
From: Joerg Roedel <jroedel@...e.de>
Date: Wed, 4 Feb 2015 15:50:38 +0100
Subject: [PATCH 1/2] iommu/amd: Use wait_event in put_pasid_state_wait

Now that I learned about possible spurious wakeups this
place needs fixing too. Replace the self-coded sleep variant
with the generic wait_event() helper.

Signed-off-by: Joerg Roedel <jroedel@...e.de>
---
 drivers/iommu/amd_iommu_v2.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/amd_iommu_v2.c b/drivers/iommu/amd_iommu_v2.c
index b6398d7..e01bc8f 100644
--- a/drivers/iommu/amd_iommu_v2.c
+++ b/drivers/iommu/amd_iommu_v2.c
@@ -266,14 +266,13 @@ static void put_pasid_state(struct pasid_state *pasid_state)
 
 static void put_pasid_state_wait(struct pasid_state *pasid_state)
 {
-	DEFINE_WAIT(wait);
+	/* Drop our reference */
+	atomic_dec(&pasid_state->count);
 
-	prepare_to_wait(&pasid_state->wq, &wait, TASK_UNINTERRUPTIBLE);
+	/* Wait for others to drop their references */
+	wait_event(pasid_state->wq, !atomic_read(&pasid_state->count));
 
-	if (!atomic_dec_and_test(&pasid_state->count))
-		schedule();
-
-	finish_wait(&pasid_state->wq, &wait);
+	/* Get rid of it */
 	free_pasid_state(pasid_state);
 }
 
-- 
1.8.4.5

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