| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 31/51] scsi, bnx2i: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:40:16 +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_maps_update_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_maps_update_done();
Fix the bnx2i 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: linux-scsi@vger.kernel.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
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..5c4e413 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_maps_update_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_maps_update_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_maps_update_begin(); for_each_online_cpu(cpu) bnx2i_percpu_thread_destroy(cpu); + __unregister_hotcpu_notifier(&bnx2i_cpu_notifier); + + cpu_maps_update_done(); + iscsi_unregister_transport(&bnx2i_iscsi_transport); cnic_unregister_driver(CNIC_ULP_ISCSI); }
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