[IA64] Add hotplug cpu to salinfo.c, replace semaphore with mutex

Add hotplug cpu support to salinfo.c.

The cpu_event field is a cpumask so use the cpu_* macros consistently,
replacing the existing mixture of cpu_* and *_bit macros.

Instead of counting the number of outstanding events in a semaphore and
trying to track that count over user space context, interrupt context,
non-maskable interrupt context and cpu hotplug, replace the semaphore
with a test for "any bits set" combined with a mutex.

Modify the locking to make the test for "work to do" an atomic
operation.

Signed-off-by: Keith Owens <kaos@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 119 insertions, 51 deletions

diff --git a/arch/ia64/kernel/salinfo.c b/arch/ia64/kernel/salinfo.c
index a87a162a3086..9d5a823479a3 100644
--- a/arch/ia64/kernel/salinfo.c
+++ b/arch/ia64/kernel/salinfo.c
@@ -3,7 +3,7 @@
  *
  * Creates entries in /proc/sal for various system features.
  *
- * Copyright (c) 2003 Silicon Graphics, Inc.  All rights reserved.
+ * Copyright (c) 2003, 2006 Silicon Graphics, Inc.  All rights reserved.
  * Copyright (c) 2003 Hewlett-Packard Co
  *      Bjorn Helgaas <bjorn.helgaas@hp.com>
  *
@@ -27,9 +27,17 @@
  *   mca.c may not pass a buffer, a NULL buffer just indicates that a new
  *   record is available in SAL.
  *   Replace some NR_CPUS by cpus_online, for hotplug cpu.
+ *
+ * Jan  5 2006        kaos@sgi.com
+ *   Handle hotplug cpus coming online.
+ *   Handle hotplug cpus going offline while they still have outstanding records.
+ *   Use the cpu_* macros consistently.
+ *   Replace the counting semaphore with a mutex and a test if the cpumask is non-empty.
+ *   Modify the locking to make the test for "work to do" an atomic operation.
  */
 
 #include <linux/capability.h>
+#include <linux/cpu.h>
 #include <linux/types.h>
 #include <linux/proc_fs.h>
 #include <linux/module.h>
@@ -132,8 +140,8 @@ enum salinfo_state {
 };
 
 struct salinfo_data {
-        volatile cpumask_t      cpu_event;      /* which cpus have outstanding events */
-        struct semaphore        sem;            /* count of cpus with outstanding events (bits set in cpu_event) */
+        cpumask_t               cpu_event;      /* which cpus have outstanding events */
+        struct semaphore        mutex;
         u8                      *log_buffer;
         u64                     log_size;
         u8                      *oemdata;       /* decoded oem data */
@@ -174,6 +182,21 @@ 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)
+{
+        down_trylock(&data->mutex);
+        up(&data->mutex);
+}
+
 static void
 salinfo_platform_oemdata_cpu(void *context)
 {
@@ -212,9 +235,9 @@ salinfo_log_wakeup(int type, u8 *buffer, u64 size, int irqsafe)
 
         BUG_ON(type >= ARRAY_SIZE(salinfo_log_name));
 
+        if (irqsafe)
+                spin_lock_irqsave(&data_saved_lock, flags);
         if (buffer) {
-                if (irqsafe)
-                        spin_lock_irqsave(&data_saved_lock, flags);
                 for (i = 0, data_saved = data->data_saved; i < saved_size; ++i, ++data_saved) {
                         if (!data_saved->buffer)
                                 break;
@@ -232,13 +255,11 @@ salinfo_log_wakeup(int type, u8 *buffer, u64 size, int irqsafe)
                         data_saved->size = size;
                         data_saved->buffer = buffer;
                 }
-                if (irqsafe)
-                        spin_unlock_irqrestore(&data_saved_lock, flags);
         }
-
-        if (!test_and_set_bit(smp_processor_id(), &data->cpu_event)) {
-                if (irqsafe)
-                        up(&data->sem);
+        cpu_set(smp_processor_id(), data->cpu_event);
+        if (irqsafe) {
+                salinfo_work_to_do(data);
+                spin_unlock_irqrestore(&data_saved_lock, flags);
         }
 }
 
@@ -249,20 +270,17 @@ static struct timer_list salinfo_timer;
 static void
 salinfo_timeout_check(struct salinfo_data *data)
 {
-        int i;
+        unsigned long flags;
         if (!data->open)
                 return;
-        for_each_online_cpu(i) {
-                if (test_bit(i, &data->cpu_event)) {
-                        /* double up() is not a problem, user space will see no
-                         * records for the additional "events".
-                         */
-                        up(&data->sem);
-                }
+        if (!cpus_empty(data->cpu_event)) {
+                spin_lock_irqsave(&data_saved_lock, flags);
+                salinfo_work_to_do(data);
+                spin_unlock_irqrestore(&data_saved_lock, flags);
         }
 }
 
-static void 
+static void
 salinfo_timeout (unsigned long arg)
 {
         salinfo_timeout_check(salinfo_data + SAL_INFO_TYPE_MCA);
@@ -290,16 +308,20 @@ salinfo_event_read(struct file *file, char __user *buffer, size_t count, loff_t
         int i, n, cpu = -1;
 
 retry:
-        if (down_trylock(&data->sem)) {
+        if (cpus_empty(data->cpu_event) && down_trylock(&data->mutex)) {
                 if (file->f_flags & O_NONBLOCK)
                         return -EAGAIN;
-                if (down_interruptible(&data->sem))
+                if (down_interruptible(&data->mutex))
                         return -EINTR;
         }
 
         n = data->cpu_check;
         for (i = 0; i < NR_CPUS; i++) {
-                if (test_bit(n, &data->cpu_event) && cpu_online(n)) {
+                if (cpu_isset(n, data->cpu_event)) {
+                        if (!cpu_online(n)) {
+                                cpu_clear(n, data->cpu_event);
+                                continue;
+                        }
                         cpu = n;
                         break;
                 }
@@ -310,9 +332,6 @@ retry:
         if (cpu == -1)
                 goto retry;
 
-        /* events are sticky until the user says "clear" */
-        up(&data->sem);
-
         /* for next read, start checking at next CPU */
         data->cpu_check = cpu;
         if (++data->cpu_check == NR_CPUS)
@@ -381,10 +400,8 @@ salinfo_log_release(struct inode *inode, struct file *file)
 static void
 call_on_cpu(int cpu, void (*fn)(void *), void *arg)
 {
-        cpumask_t save_cpus_allowed, new_cpus_allowed;
-        memcpy(&save_cpus_allowed, &current->cpus_allowed, sizeof(save_cpus_allowed));
-        memset(&new_cpus_allowed, 0, sizeof(new_cpus_allowed));
-        set_bit(cpu, &new_cpus_allowed);
+        cpumask_t save_cpus_allowed = current->cpus_allowed;
+        cpumask_t new_cpus_allowed = cpumask_of_cpu(cpu);
         set_cpus_allowed(current, new_cpus_allowed);
         (*fn)(arg);
         set_cpus_allowed(current, save_cpus_allowed);
@@ -433,10 +450,10 @@ retry:
         if (!data->saved_num)
                 call_on_cpu(cpu, salinfo_log_read_cpu, data);
         if (!data->log_size) {
-                data->state = STATE_NO_DATA;
-                clear_bit(cpu, &data->cpu_event);
+                data->state = STATE_NO_DATA;
+                cpu_clear(cpu, data->cpu_event);
         } else {
-                data->state = STATE_LOG_RECORD;
+                data->state = STATE_LOG_RECORD;
         }
 }
 
@@ -473,27 +490,31 @@ static int
 salinfo_log_clear(struct salinfo_data *data, int cpu)
 {
         sal_log_record_header_t *rh;
+        unsigned long flags;
+        spin_lock_irqsave(&data_saved_lock, flags);
         data->state = STATE_NO_DATA;
-        if (!test_bit(cpu, &data->cpu_event))
+        if (!cpu_isset(cpu, data->cpu_event)) {
+                spin_unlock_irqrestore(&data_saved_lock, flags);
                 return 0;
-        down(&data->sem);
-        clear_bit(cpu, &data->cpu_event);
+        }
+        cpu_clear(cpu, data->cpu_event);
         if (data->saved_num) {
-                unsigned long flags;
-                spin_lock_irqsave(&data_saved_lock, flags);
-                shift1_data_saved(data, data->saved_num - 1 );
+                shift1_data_saved(data, data->saved_num - 1);
                 data->saved_num = 0;
-                spin_unlock_irqrestore(&data_saved_lock, flags);
         }
+        spin_unlock_irqrestore(&data_saved_lock, flags);
         rh = (sal_log_record_header_t *)(data->log_buffer);
         /* Corrected errors have already been cleared from SAL */
         if (rh->severity != sal_log_severity_corrected)
                 call_on_cpu(cpu, salinfo_log_clear_cpu, data);
         /* clearing a record may make a new record visible */
         salinfo_log_new_read(cpu, data);
-        if (data->state == STATE_LOG_RECORD &&
-            !test_and_set_bit(cpu,  &data->cpu_event))
-                up(&data->sem);
+        if (data->state == STATE_LOG_RECORD) {
+                spin_lock_irqsave(&data_saved_lock, flags);
+                cpu_set(cpu, data->cpu_event);
+                salinfo_work_to_do(data);
+                spin_unlock_irqrestore(&data_saved_lock, flags);
+        }
         return 0;
 }
 
@@ -550,6 +571,53 @@ static struct file_operations salinfo_data_fops = {
         .write   = salinfo_log_write,
 };
 
+#ifdef  CONFIG_HOTPLUG_CPU
+static int __devinit
+salinfo_cpu_callback(struct notifier_block *nb, unsigned long action, void *hcpu)
+{
+        unsigned int i, cpu = (unsigned long)hcpu;
+        unsigned long flags;
+        struct salinfo_data *data;
+        switch (action) {
+        case CPU_ONLINE:
+                spin_lock_irqsave(&data_saved_lock, flags);
+                for (i = 0, data = salinfo_data;
+                     i < ARRAY_SIZE(salinfo_data);
+                     ++i, ++data) {
+                        cpu_set(cpu, data->cpu_event);
+                        salinfo_work_to_do(data);
+                }
+                spin_unlock_irqrestore(&data_saved_lock, flags);
+                break;
+        case CPU_DEAD:
+                spin_lock_irqsave(&data_saved_lock, flags);
+                for (i = 0, data = salinfo_data;
+                     i < ARRAY_SIZE(salinfo_data);
+                     ++i, ++data) {
+                        struct salinfo_data_saved *data_saved;
+                        int j;
+                        for (j = ARRAY_SIZE(data->data_saved) - 1, data_saved = data->data_saved + j;
+                             j >= 0;
+                             --j, --data_saved) {
+                                if (data_saved->buffer && data_saved->cpu == cpu) {
+                                        shift1_data_saved(data, j);
+                                }
+                        }
+                        cpu_clear(cpu, data->cpu_event);
+                }
+                spin_unlock_irqrestore(&data_saved_lock, flags);
+                break;
+        }
+        return NOTIFY_OK;
+}
+
+static struct notifier_block salinfo_cpu_notifier =
+{
+        .notifier_call = salinfo_cpu_callback,
+        .priority = 0,
+};
+#endif  /* CONFIG_HOTPLUG_CPU */
+
 static int __init
 salinfo_init(void)
 {
@@ -557,7 +625,7 @@ salinfo_init(void)
         struct proc_dir_entry **sdir = salinfo_proc_entries; /* keeps track of every entry */
         struct proc_dir_entry *dir, *entry;
         struct salinfo_data *data;
-        int i, j, online;
+        int i, j;
 
         salinfo_dir = proc_mkdir("sal", NULL);
         if (!salinfo_dir)
@@ -572,7 +640,7 @@ salinfo_init(void)
         for (i = 0; i < ARRAY_SIZE(salinfo_log_name); i++) {
                 data = salinfo_data + i;
                 data->type = i;
-                sema_init(&data->sem, 0);
+                init_MUTEX(&data->mutex);
                 dir = proc_mkdir(salinfo_log_name[i], salinfo_dir);
                 if (!dir)
                         continue;
@@ -592,12 +660,8 @@ salinfo_init(void)
                 *sdir++ = entry;
 
                 /* we missed any events before now */
-                online = 0;
-                for_each_online_cpu(j) {
-                        set_bit(j, &data->cpu_event);
-                        ++online;
-                }
-                sema_init(&data->sem, online);
+                for_each_online_cpu(j)
+                        cpu_set(j, data->cpu_event);
 
                 *sdir++ = dir;
         }
@@ -609,6 +673,10 @@ salinfo_init(void)
         salinfo_timer.function = &salinfo_timeout;
         add_timer(&salinfo_timer);
 
+#ifdef  CONFIG_HOTPLUG_CPU
+        register_cpu_notifier(&salinfo_cpu_notifier);
+#endif
+
         return 0;
 }