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>

1 files changed, 10 insertions, 28 deletions

diff --git a/arch/ia64/kernel/salinfo.c b/arch/ia64/kernel/salinfo.c
index 1eeffb7fbb16..5313007d5423 100644
--- a/arch/ia64/kernel/salinfo.c
+++ b/arch/ia64/kernel/salinfo.c
@@ -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;