[PATCH v2 33/52] scsi, bnx2i: Fix CPU hotplug callback registration

From: Srivatsa S. Bhat
Date: Fri Feb 14 2014 - 03:02:26 EST


Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

get_online_cpus();

for_each_online_cpu(cpu)
init_cpu(cpu);

register_cpu_notifier(&foobar_cpu_notifier);

put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

cpu_notifier_register_begin();

for_each_online_cpu(cpu)
init_cpu(cpu);

/* Note the use of the double underscored version of the API */
__register_cpu_notifier(&foobar_cpu_notifier);

cpu_notifier_register_done();


Fix the bnx2i code in scsi by using this latter form of callback registration.

Cc: Eddie Wai <eddie.wai@xxxxxxxxxxxx>
Cc: "James E.J. Bottomley" <JBottomley@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: linux-scsi@xxxxxxxxxxxxxxx
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

drivers/scsi/bnx2i/bnx2i_init.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/bnx2i/bnx2i_init.c b/drivers/scsi/bnx2i/bnx2i_init.c
index 34c294b..80c03b4 100644
--- a/drivers/scsi/bnx2i/bnx2i_init.c
+++ b/drivers/scsi/bnx2i/bnx2i_init.c
@@ -537,11 +537,15 @@ static int __init bnx2i_mod_init(void)
p->iothread = NULL;
}

+ cpu_notifier_register_begin();
+
for_each_online_cpu(cpu)
bnx2i_percpu_thread_create(cpu);

/* Initialize per CPU interrupt thread */
- register_hotcpu_notifier(&bnx2i_cpu_notifier);
+ __register_hotcpu_notifier(&bnx2i_cpu_notifier);
+
+ cpu_notifier_register_done();

return 0;

@@ -581,11 +585,15 @@ static void __exit bnx2i_mod_exit(void)
}
mutex_unlock(&bnx2i_dev_lock);

- unregister_hotcpu_notifier(&bnx2i_cpu_notifier);
+ cpu_notifier_register_begin();

for_each_online_cpu(cpu)
bnx2i_percpu_thread_destroy(cpu);

+ __unregister_hotcpu_notifier(&bnx2i_cpu_notifier);
+
+ cpu_notifier_register_done();
+
iscsi_unregister_transport(&bnx2i_iscsi_transport);
cnic_unregister_driver(CNIC_ULP_ISCSI);
}

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