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Commit fbb0e4da authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Tony Luck
Browse files

ia64: salinfo: use a waitqueue instead a sema down/up combo 



The only purpose of down_try_lock() followed by up() seems to be to wake
up a possible reader. This patch replaces it with a wake-queue. There is
no locking around cpumask_empty() and the test is re-done in case there
was no hit.
With wait_event_interruptible_lock_irq(,&data_saved_lock) we would probably
be able to get rid of the `retry` label. However we still can return CPU
X which is valid now but later (after the lock dropped) the event may
have been removed because the CPU went offline.

Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarTony Luck <tony.luck@intel.com>
parent 70f4f935

arch/ia64/kernel/salinfo.c

+10 −28
Original line number Diff line number Diff line
@@ -141,7 +141,7 @@ enum salinfo_state { 


struct salinfo_data {

	cpumask_t		cpu_event;	/* which cpus have outstanding events */

	struct semaphore	mutex;

	wait_queue_head_t	read_wait;

	u8			*log_buffer;

	u64			log_size;

	u8			*oemdata;	/* decoded oem data */
@@ -182,21 +182,6 @@ struct salinfo_platform_oemdata_parms { 
	int ret;

};



/* Kick the mutex that tells user space that there is work to do.  Instead of

 * trying to track the state of the mutex across multiple cpus, in user

 * context, interrupt context, non-maskable interrupt context and hotplug cpu,

 * it is far easier just to grab the mutex if it is free then release it.

 *

 * This routine must be called with data_saved_lock held, to make the down/up

 * operation atomic.

 */

static void

salinfo_work_to_do(struct salinfo_data *data)

{

	(void)(down_trylock(&data->mutex) ?: 0);

	up(&data->mutex);

}



static void

salinfo_platform_oemdata_cpu(void *context)

{
@@ -258,7 +243,7 @@ salinfo_log_wakeup(int type, u8 *buffer, u64 size, int irqsafe) 
	}

	cpumask_set_cpu(smp_processor_id(), &data->cpu_event);

	if (irqsafe) {

		salinfo_work_to_do(data);

		wake_up_interruptible(&data->read_wait);

		spin_unlock_irqrestore(&data_saved_lock, flags);

	}

}
@@ -271,14 +256,10 @@ extern void ia64_mlogbuf_dump(void); 
static void

salinfo_timeout_check(struct salinfo_data *data)

{

	unsigned long flags;

	if (!data->open)

		return;

	if (!cpumask_empty(&data->cpu_event)) {

		spin_lock_irqsave(&data_saved_lock, flags);

		salinfo_work_to_do(data);

		spin_unlock_irqrestore(&data_saved_lock, flags);

	}

	if (!cpumask_empty(&data->cpu_event))

		wake_up_interruptible(&data->read_wait);

}



static void
@@ -308,10 +289,11 @@ salinfo_event_read(struct file *file, char __user *buffer, size_t count, loff_t 
	int i, n, cpu = -1;



retry:

	if (cpumask_empty(&data->cpu_event) && down_trylock(&data->mutex)) {

	if (cpumask_empty(&data->cpu_event)) {

		if (file->f_flags & O_NONBLOCK)

			return -EAGAIN;

		if (down_interruptible(&data->mutex))

		if (wait_event_interruptible(data->read_wait,

					     !cpumask_empty(&data->cpu_event)))

			return -EINTR;

	}
@@ -510,7 +492,7 @@ salinfo_log_clear(struct salinfo_data *data, int cpu) 
	if (data->state == STATE_LOG_RECORD) {

		spin_lock_irqsave(&data_saved_lock, flags);

		cpumask_set_cpu(cpu, &data->cpu_event);

		salinfo_work_to_do(data);

		wake_up_interruptible(&data->read_wait);

		spin_unlock_irqrestore(&data_saved_lock, flags);

	}

	return 0;
@@ -582,7 +564,7 @@ salinfo_cpu_callback(struct notifier_block *nb, unsigned long action, void *hcpu 
		     i < ARRAY_SIZE(salinfo_data);

		     ++i, ++data) {

			cpumask_set_cpu(cpu, &data->cpu_event);

			salinfo_work_to_do(data);

			wake_up_interruptible(&data->read_wait);

		}

		spin_unlock_irqrestore(&data_saved_lock, flags);

		break;
@@ -640,7 +622,7 @@ salinfo_init(void) 
	for (i = 0; i < ARRAY_SIZE(salinfo_log_name); i++) {

		data = salinfo_data + i;

		data->type = i;

		sema_init(&data->mutex, 1);

		init_waitqueue_head(&data->read_wait);

		dir = proc_mkdir(salinfo_log_name[i], salinfo_dir);

		if (!dir)

			continue;