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From: Jason Gunthorpe <jgg@ziepe.ca>
To: linux-rdma@vger.kernel.org
Cc: Jason Gunthorpe <jgg@mellanox.com>,
	Artemy Kovalyov <artemyko@mellanox.com>
Subject: [PATCH 4/6] RDMA/mlx5: Order num_pending_prefetch properly with synchronize_srcu
Date: Tue,  1 Oct 2019 12:38:19 -0300
Message-ID: <20191001153821.23621-5-jgg@ziepe.ca> (raw)
In-Reply-To: <20191001153821.23621-1-jgg@ziepe.ca>

From: Jason Gunthorpe <jgg@mellanox.com>

During destroy setting live = 0 and then synchronize_srcu() prevents
num_pending_prefetch from incrementing, and also, ensures that all work
holding that count is queued on the WQ. Testing before causes races of the
form:

    CPU0                                         CPU1
  dereg_mr()
                                          mlx5_ib_advise_mr_prefetch()
            				   srcu_read_lock()
                                            num_pending_prefetch_inc()
					      if (!live)
   live = 0
   atomic_read() == 0
     // skip flush_workqueue()
                                              atomic_inc()
 					      queue_work();
            				   srcu_read_unlock()
   WARN_ON(atomic_read())  // Fails

Swap the order so that the synchronize_srcu() prevents this.

Fixes: a6bc3875f176 ("IB/mlx5: Protect against prefetch of invalid MR")
Reviewed-by: Artemy Kovalyov <artemyko@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
---
 drivers/infiniband/hw/mlx5/mr.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
index e7f840f306e46a..0ee8fa01177fc9 100644
--- a/drivers/infiniband/hw/mlx5/mr.c
+++ b/drivers/infiniband/hw/mlx5/mr.c
@@ -1609,13 +1609,14 @@ static void dereg_mr(struct mlx5_ib_dev *dev, struct mlx5_ib_mr *mr)
 		 */
 		mr->live = 0;
 
+		/* Wait for all running page-fault handlers to finish. */
+		synchronize_srcu(&dev->mr_srcu);
+
 		/* dequeue pending prefetch requests for the mr */
 		if (atomic_read(&mr->num_pending_prefetch))
 			flush_workqueue(system_unbound_wq);
 		WARN_ON(atomic_read(&mr->num_pending_prefetch));
 
-		/* Wait for all running page-fault handlers to finish. */
-		synchronize_srcu(&dev->mr_srcu);
 		/* Destroy all page mappings */
 		if (!umem_odp->is_implicit_odp)
 			mlx5_ib_invalidate_range(umem_odp,
-- 
2.23.0


  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-01 15:38 [PATCH -rc 0/6] Bug fixes for odp Jason Gunthorpe
2019-10-01 15:38 ` [PATCH 1/6] RDMA/mlx5: Do not allow rereg of a ODP MR Jason Gunthorpe
2019-10-01 15:38 ` [PATCH 2/6] RDMA/mlx5: Fix a race with mlx5_ib_update_xlt on an implicit MR Jason Gunthorpe
2019-10-02  8:18   ` Leon Romanovsky
2019-10-02 14:39     ` Jason Gunthorpe
2019-10-02 15:41       ` Leon Romanovsky
2019-10-03 12:48         ` Jason Gunthorpe
2019-10-01 15:38 ` [PATCH 3/6] RDMA/odp: Lift umem_mutex out of ib_umem_odp_unmap_dma_pages() Jason Gunthorpe
2019-10-01 15:38 ` Jason Gunthorpe [this message]
2019-10-01 15:38 ` [PATCH 5/6] RDMA/mlx5: Put live in the correct place for ODP MRs Jason Gunthorpe
2019-10-01 15:38 ` [PATCH 6/6] RDMA/mlx5: Add missing synchronize_srcu() for MW cases Jason Gunthorpe
2019-10-03  8:54   ` Leon Romanovsky
2019-10-03 12:33     ` Jason Gunthorpe
2019-10-04 18:55 ` [PATCH -rc 0/6] Bug fixes for odp Jason Gunthorpe

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