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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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>
This commit is contained in:
Sebastian Andrzej Siewior 2016-07-25 10:43:13 +02:00 committed by Tony Luck
parent 70f4f93523
commit fbb0e4da96
1 changed files with 10 additions and 28 deletions
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38
arch/ia64/kernel/salinfo.c
View File

@ -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;