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From:   "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To:     linux-kernel@vger.kernel.org
Cc:     mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
        rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
        fweisbec@gmail.com, oleg@redhat.com, joel.opensrc@gmail.com,
        Nitzan Carmi <nitzanc@mellanox.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 12/22] nvme: Avoid flush dependency in delete controller flow
Date:   Sun, 22 Apr 2018 19:32:17 -0700
In-Reply-To: <20180423023150.GA21533@linux.vnet.ibm.com>
References: <20180423023150.GA21533@linux.vnet.ibm.com>
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From: Nitzan Carmi <nitzanc@mellanox.com>

The nvme_delete_ctrl() function queues a work item on a MEM_RECLAIM
queue (nvme_delete_wq), which eventually calls cleanup_srcu_struct(),
which in turn flushes a delayed work from an !MEM_RECLAIM queue. This
is unsafe as we might trigger deadlocks under severe memory pressure.

Since we don't ever invoke call_srcu(), it is safe to use the shiny new
_quiesced() version of srcu cleanup, thus avoiding that flush dependency.
This commit makes that change.

Signed-off-by: Nitzan Carmi <nitzanc@mellanox.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
---
 drivers/nvme/host/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 9df4f71e58ca..c3cea8a29843 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -349,7 +349,7 @@ static void nvme_free_ns_head(struct kref *ref)
 	nvme_mpath_remove_disk(head);
 	ida_simple_remove(&head->subsys->ns_ida, head->instance);
 	list_del_init(&head->entry);
-	cleanup_srcu_struct(&head->srcu);
+	cleanup_srcu_struct_quiesced(&head->srcu);
 	kfree(head);
 }
 
-- 
2.5.2