summaryrefslogtreecommitdiff
path: root/kernel/printk/printk.c
diff options
context:
space:
mode:
Diffstat (limited to 'kernel/printk/printk.c')
-rw-r--r--kernel/printk/printk.c116
1 files changed, 116 insertions, 0 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 421c35571797..142a58d124d9 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3531,3 +3531,119 @@ void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
#endif
+
+#ifdef CONFIG_SMP
+static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1);
+static atomic_t printk_cpulock_nested = ATOMIC_INIT(0);
+
+/**
+ * __printk_wait_on_cpu_lock() - Busy wait until the printk cpu-reentrant
+ * spinning lock is not owned by any CPU.
+ *
+ * Context: Any context.
+ */
+void __printk_wait_on_cpu_lock(void)
+{
+ do {
+ cpu_relax();
+ } while (atomic_read(&printk_cpulock_owner) != -1);
+}
+EXPORT_SYMBOL(__printk_wait_on_cpu_lock);
+
+/**
+ * __printk_cpu_trylock() - Try to acquire the printk cpu-reentrant
+ * spinning lock.
+ *
+ * If no processor has the lock, the calling processor takes the lock and
+ * becomes the owner. If the calling processor is already the owner of the
+ * lock, this function succeeds immediately.
+ *
+ * Context: Any context. Expects interrupts to be disabled.
+ * Return: 1 on success, otherwise 0.
+ */
+int __printk_cpu_trylock(void)
+{
+ int cpu;
+ int old;
+
+ cpu = smp_processor_id();
+
+ /*
+ * Guarantee loads and stores from this CPU when it is the lock owner
+ * are _not_ visible to the previous lock owner. This pairs with
+ * __printk_cpu_unlock:B.
+ *
+ * Memory barrier involvement:
+ *
+ * If __printk_cpu_trylock:A reads from __printk_cpu_unlock:B, then
+ * __printk_cpu_unlock:A can never read from __printk_cpu_trylock:B.
+ *
+ * Relies on:
+ *
+ * RELEASE from __printk_cpu_unlock:A to __printk_cpu_unlock:B
+ * of the previous CPU
+ * matching
+ * ACQUIRE from __printk_cpu_trylock:A to __printk_cpu_trylock:B
+ * of this CPU
+ */
+ old = atomic_cmpxchg_acquire(&printk_cpulock_owner, -1,
+ cpu); /* LMM(__printk_cpu_trylock:A) */
+ if (old == -1) {
+ /*
+ * This CPU is now the owner and begins loading/storing
+ * data: LMM(__printk_cpu_trylock:B)
+ */
+ return 1;
+
+ } else if (old == cpu) {
+ /* This CPU is already the owner. */
+ atomic_inc(&printk_cpulock_nested);
+ return 1;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(__printk_cpu_trylock);
+
+/**
+ * __printk_cpu_unlock() - Release the printk cpu-reentrant spinning lock.
+ *
+ * The calling processor must be the owner of the lock.
+ *
+ * Context: Any context. Expects interrupts to be disabled.
+ */
+void __printk_cpu_unlock(void)
+{
+ if (atomic_read(&printk_cpulock_nested)) {
+ atomic_dec(&printk_cpulock_nested);
+ return;
+ }
+
+ /*
+ * This CPU is finished loading/storing data:
+ * LMM(__printk_cpu_unlock:A)
+ */
+
+ /*
+ * Guarantee loads and stores from this CPU when it was the
+ * lock owner are visible to the next lock owner. This pairs
+ * with __printk_cpu_trylock:A.
+ *
+ * Memory barrier involvement:
+ *
+ * If __printk_cpu_trylock:A reads from __printk_cpu_unlock:B,
+ * then __printk_cpu_trylock:B reads from __printk_cpu_unlock:A.
+ *
+ * Relies on:
+ *
+ * RELEASE from __printk_cpu_unlock:A to __printk_cpu_unlock:B
+ * of this CPU
+ * matching
+ * ACQUIRE from __printk_cpu_trylock:A to __printk_cpu_trylock:B
+ * of the next CPU
+ */
+ atomic_set_release(&printk_cpulock_owner,
+ -1); /* LMM(__printk_cpu_unlock:B) */
+}
+EXPORT_SYMBOL(__printk_cpu_unlock);
+#endif /* CONFIG_SMP */