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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /lib/kernel_lock.c
downloadlinux-2.6.38-lt-ux500-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'lib/kernel_lock.c')
-rw-r--r--lib/kernel_lock.c264
1 files changed, 264 insertions, 0 deletions
diff --git a/lib/kernel_lock.c b/lib/kernel_lock.c
new file mode 100644
index 00000000000..99b0ae3d51d
--- /dev/null
+++ b/lib/kernel_lock.c
@@ -0,0 +1,264 @@
+/*
+ * lib/kernel_lock.c
+ *
+ * This is the traditional BKL - big kernel lock. Largely
+ * relegated to obsolescense, but used by various less
+ * important (or lazy) subsystems.
+ */
+#include <linux/smp_lock.h>
+#include <linux/module.h>
+#include <linux/kallsyms.h>
+
+#if defined(CONFIG_PREEMPT) && defined(__smp_processor_id) && \
+ defined(CONFIG_DEBUG_PREEMPT)
+
+/*
+ * Debugging check.
+ */
+unsigned int smp_processor_id(void)
+{
+ unsigned long preempt_count = preempt_count();
+ int this_cpu = __smp_processor_id();
+ cpumask_t this_mask;
+
+ if (likely(preempt_count))
+ goto out;
+
+ if (irqs_disabled())
+ goto out;
+
+ /*
+ * Kernel threads bound to a single CPU can safely use
+ * smp_processor_id():
+ */
+ this_mask = cpumask_of_cpu(this_cpu);
+
+ if (cpus_equal(current->cpus_allowed, this_mask))
+ goto out;
+
+ /*
+ * It is valid to assume CPU-locality during early bootup:
+ */
+ if (system_state != SYSTEM_RUNNING)
+ goto out;
+
+ /*
+ * Avoid recursion:
+ */
+ preempt_disable();
+
+ if (!printk_ratelimit())
+ goto out_enable;
+
+ printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] code: %s/%d\n", preempt_count(), current->comm, current->pid);
+ print_symbol("caller is %s\n", (long)__builtin_return_address(0));
+ dump_stack();
+
+out_enable:
+ preempt_enable_no_resched();
+out:
+ return this_cpu;
+}
+
+EXPORT_SYMBOL(smp_processor_id);
+
+#endif /* PREEMPT && __smp_processor_id && DEBUG_PREEMPT */
+
+#ifdef CONFIG_PREEMPT_BKL
+/*
+ * The 'big kernel semaphore'
+ *
+ * This mutex is taken and released recursively by lock_kernel()
+ * and unlock_kernel(). It is transparently dropped and reaquired
+ * over schedule(). It is used to protect legacy code that hasn't
+ * been migrated to a proper locking design yet.
+ *
+ * Note: code locked by this semaphore will only be serialized against
+ * other code using the same locking facility. The code guarantees that
+ * the task remains on the same CPU.
+ *
+ * Don't use in new code.
+ */
+static DECLARE_MUTEX(kernel_sem);
+
+/*
+ * Re-acquire the kernel semaphore.
+ *
+ * This function is called with preemption off.
+ *
+ * We are executing in schedule() so the code must be extremely careful
+ * about recursion, both due to the down() and due to the enabling of
+ * preemption. schedule() will re-check the preemption flag after
+ * reacquiring the semaphore.
+ */
+int __lockfunc __reacquire_kernel_lock(void)
+{
+ struct task_struct *task = current;
+ int saved_lock_depth = task->lock_depth;
+
+ BUG_ON(saved_lock_depth < 0);
+
+ task->lock_depth = -1;
+ preempt_enable_no_resched();
+
+ down(&kernel_sem);
+
+ preempt_disable();
+ task->lock_depth = saved_lock_depth;
+
+ return 0;
+}
+
+void __lockfunc __release_kernel_lock(void)
+{
+ up(&kernel_sem);
+}
+
+/*
+ * Getting the big kernel semaphore.
+ */
+void __lockfunc lock_kernel(void)
+{
+ struct task_struct *task = current;
+ int depth = task->lock_depth + 1;
+
+ if (likely(!depth))
+ /*
+ * No recursion worries - we set up lock_depth _after_
+ */
+ down(&kernel_sem);
+
+ task->lock_depth = depth;
+}
+
+void __lockfunc unlock_kernel(void)
+{
+ struct task_struct *task = current;
+
+ BUG_ON(task->lock_depth < 0);
+
+ if (likely(--task->lock_depth < 0))
+ up(&kernel_sem);
+}
+
+#else
+
+/*
+ * The 'big kernel lock'
+ *
+ * This spinlock is taken and released recursively by lock_kernel()
+ * and unlock_kernel(). It is transparently dropped and reaquired
+ * over schedule(). It is used to protect legacy code that hasn't
+ * been migrated to a proper locking design yet.
+ *
+ * Don't use in new code.
+ */
+static __cacheline_aligned_in_smp DEFINE_SPINLOCK(kernel_flag);
+
+
+/*
+ * Acquire/release the underlying lock from the scheduler.
+ *
+ * This is called with preemption disabled, and should
+ * return an error value if it cannot get the lock and
+ * TIF_NEED_RESCHED gets set.
+ *
+ * If it successfully gets the lock, it should increment
+ * the preemption count like any spinlock does.
+ *
+ * (This works on UP too - _raw_spin_trylock will never
+ * return false in that case)
+ */
+int __lockfunc __reacquire_kernel_lock(void)
+{
+ while (!_raw_spin_trylock(&kernel_flag)) {
+ if (test_thread_flag(TIF_NEED_RESCHED))
+ return -EAGAIN;
+ cpu_relax();
+ }
+ preempt_disable();
+ return 0;
+}
+
+void __lockfunc __release_kernel_lock(void)
+{
+ _raw_spin_unlock(&kernel_flag);
+ preempt_enable_no_resched();
+}
+
+/*
+ * These are the BKL spinlocks - we try to be polite about preemption.
+ * If SMP is not on (ie UP preemption), this all goes away because the
+ * _raw_spin_trylock() will always succeed.
+ */
+#ifdef CONFIG_PREEMPT
+static inline void __lock_kernel(void)
+{
+ preempt_disable();
+ if (unlikely(!_raw_spin_trylock(&kernel_flag))) {
+ /*
+ * If preemption was disabled even before this
+ * was called, there's nothing we can be polite
+ * about - just spin.
+ */
+ if (preempt_count() > 1) {
+ _raw_spin_lock(&kernel_flag);
+ return;
+ }
+
+ /*
+ * Otherwise, let's wait for the kernel lock
+ * with preemption enabled..
+ */
+ do {
+ preempt_enable();
+ while (spin_is_locked(&kernel_flag))
+ cpu_relax();
+ preempt_disable();
+ } while (!_raw_spin_trylock(&kernel_flag));
+ }
+}
+
+#else
+
+/*
+ * Non-preemption case - just get the spinlock
+ */
+static inline void __lock_kernel(void)
+{
+ _raw_spin_lock(&kernel_flag);
+}
+#endif
+
+static inline void __unlock_kernel(void)
+{
+ _raw_spin_unlock(&kernel_flag);
+ preempt_enable();
+}
+
+/*
+ * Getting the big kernel lock.
+ *
+ * This cannot happen asynchronously, so we only need to
+ * worry about other CPU's.
+ */
+void __lockfunc lock_kernel(void)
+{
+ int depth = current->lock_depth+1;
+ if (likely(!depth))
+ __lock_kernel();
+ current->lock_depth = depth;
+}
+
+void __lockfunc unlock_kernel(void)
+{
+ BUG_ON(current->lock_depth < 0);
+ if (likely(--current->lock_depth < 0))
+ __unlock_kernel();
+}
+
+#endif
+
+EXPORT_SYMBOL(lock_kernel);
+EXPORT_SYMBOL(unlock_kernel);
+