Messages in this thread Patch in this message |  | | From | "Srivatsa S. Bhat" <> | Subject | [PATCH v2 34/52] scsi, bnx2fc: Fix CPU hotplug callback registration | Date | Fri, 14 Feb 2014 13:26:55 +0530 |
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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 bnx2fc code in scsi by using this latter form of callback registration.
Cc: Eddie Wai <eddie.wai@broadcom.com> Cc: "James E.J. Bottomley" <JBottomley@parallels.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: linux-scsi@vger.kernel.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
drivers/scsi/bnx2fc/bnx2fc_fcoe.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/scsi/bnx2fc/bnx2fc_fcoe.c b/drivers/scsi/bnx2fc/bnx2fc_fcoe.c index 9b94850..c4ec235 100644 --- a/drivers/scsi/bnx2fc/bnx2fc_fcoe.c +++ b/drivers/scsi/bnx2fc/bnx2fc_fcoe.c @@ -2586,12 +2586,16 @@ static int __init bnx2fc_mod_init(void) spin_lock_init(&p->fp_work_lock); } + cpu_notifier_register_begin(); + for_each_online_cpu(cpu) { bnx2fc_percpu_thread_create(cpu); } /* Initialize per CPU interrupt thread */ - register_hotcpu_notifier(&bnx2fc_cpu_notifier); + __register_hotcpu_notifier(&bnx2fc_cpu_notifier); + + cpu_notifier_register_done(); cnic_register_driver(CNIC_ULP_FCOE, &bnx2fc_cnic_cb); @@ -2656,13 +2660,17 @@ static void __exit bnx2fc_mod_exit(void) if (l2_thread) kthread_stop(l2_thread); - unregister_hotcpu_notifier(&bnx2fc_cpu_notifier); + cpu_notifier_register_begin(); /* Destroy per cpu threads */ for_each_online_cpu(cpu) { bnx2fc_percpu_thread_destroy(cpu); } + __unregister_hotcpu_notifier(&bnx2fc_cpu_notifier); + + cpu_notifier_register_done(); + destroy_workqueue(bnx2fc_wq); /* * detach from scsi transport
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