Messages in this thread Patch in this message |  | | From | "Srivatsa S. Bhat" <> | Subject | [PATCH v2 42/52] octeon, watchdog: Fix CPU hotplug callback registration | Date | Fri, 14 Feb 2014 13:28:42 +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 watchdog code in octeon by using this latter form of callback registration.
Cc: Wim Van Sebroeck <wim@iguana.be> Cc: Ingo Molnar <mingo@kernel.org> Cc: linux-watchdog@vger.kernel.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
drivers/watchdog/octeon-wdt-main.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/drivers/watchdog/octeon-wdt-main.c b/drivers/watchdog/octeon-wdt-main.c index 4612088..4baf2d7 100644 --- a/drivers/watchdog/octeon-wdt-main.c +++ b/drivers/watchdog/octeon-wdt-main.c @@ -708,10 +708,13 @@ static int __init octeon_wdt_init(void) cpumask_clear(&irq_enabled_cpus); + cpu_notifier_register_begin(); for_each_online_cpu(cpu) octeon_wdt_setup_interrupt(cpu); - register_hotcpu_notifier(&octeon_wdt_cpu_notifier); + __register_hotcpu_notifier(&octeon_wdt_cpu_notifier); + cpu_notifier_register_done(); + out: return ret; } @@ -725,7 +728,8 @@ static void __exit octeon_wdt_cleanup(void) misc_deregister(&octeon_wdt_miscdev); - unregister_hotcpu_notifier(&octeon_wdt_cpu_notifier); + cpu_notifier_register_begin(); + __unregister_hotcpu_notifier(&octeon_wdt_cpu_notifier); for_each_online_cpu(cpu) { int core = cpu2core(cpu); @@ -734,6 +738,9 @@ static void __exit octeon_wdt_cleanup(void) /* Free the interrupt handler */ free_irq(OCTEON_IRQ_WDOG0 + core, octeon_wdt_poke_irq); } + + cpu_notifier_register_done(); + /* * Disable the boot-bus memory, the code it points to is soon * to go missing.
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