Make printk() console semaphore accesses sensible

The printk() logic on when/how to get the console semaphore was
unreadable, this splits the code up into a few helper functions and
makes it easier to follow what is going on.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 48 insertions, 35 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index 9adc2a473e6e..c46a20a19a15 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -616,6 +616,40 @@ asmlinkage int printk(const char *fmt, ...)
 /* cpu currently holding logbuf_lock */
 static volatile unsigned int printk_cpu = UINT_MAX;
 
+/*
+ * Can we actually use the console at this time on this cpu?
+ *
+ * Console drivers may assume that per-cpu resources have
+ * been allocated. So unless they're explicitly marked as
+ * being able to cope (CON_ANYTIME) don't call them until
+ * this CPU is officially up.
+ */
+static inline int can_use_console(unsigned int cpu)
+{
+        return cpu_online(cpu) || have_callable_console();
+}
+
+/*
+ * Try to get console ownership to actually show the kernel
+ * messages from a 'printk'. Return true (and with the
+ * console_semaphore held, and 'console_locked' set) if it
+ * is successful, false otherwise.
+ *
+ * This gets called with the 'logbuf_lock' spinlock held and
+ * interrupts disabled. It should return with 'lockbuf_lock'
+ * released but interrupts still disabled.
+ */
+static int acquire_console_semaphore_for_printk(unsigned int cpu)
+{
+        int retval = 0;
+
+        if (can_use_console(cpu))
+                retval = !try_acquire_console_sem();
+        printk_cpu = UINT_MAX;
+        spin_unlock(&logbuf_lock);
+        return retval;
+}
+
 const char printk_recursion_bug_msg [] =
                         KERN_CRIT "BUG: recent printk recursion!\n";
 static int printk_recursion_bug;
@@ -725,43 +759,22 @@ asmlinkage int vprintk(const char *fmt, va_list args)
                         log_level_unknown = 1;
         }
 
-        if (!down_trylock(&console_sem)) {
-                /*
-                 * We own the drivers.  We can drop the spinlock and
-                 * let release_console_sem() print the text, maybe ...
-                 */
-                console_locked = 1;
-                printk_cpu = UINT_MAX;
-                spin_unlock(&logbuf_lock);
+        /*
+         * Try to acquire and then immediately release the
+         * console semaphore. The release will do all the
+         * actual magic (print out buffers, wake up klogd,
+         * etc). 
+         *
+         * The acquire_console_semaphore_for_printk() function
+         * will release 'logbuf_lock' regardless of whether it
+         * actually gets the semaphore or not.
+         */
+        if (acquire_console_semaphore_for_printk(this_cpu))
+                release_console_sem();
 
-                /*
-                 * Console drivers may assume that per-cpu resources have
-                 * been allocated. So unless they're explicitly marked as
-                 * being able to cope (CON_ANYTIME) don't call them until
-                 * this CPU is officially up.
-                 */
-                if (cpu_online(smp_processor_id()) || have_callable_console()) {
-                        console_may_schedule = 0;
-                        release_console_sem();
-                } else {
-                        /* Release by hand to avoid flushing the buffer. */
-                        console_locked = 0;
-                        up(&console_sem);
-                }
-                lockdep_on();
-                raw_local_irq_restore(flags);
-        } else {
-                /*
-                 * Someone else owns the drivers.  We drop the spinlock, which
-                 * allows the semaphore holder to proceed and to call the
-                 * console drivers with the output which we just produced.
-                 */
-                printk_cpu = UINT_MAX;
-                spin_unlock(&logbuf_lock);
-                lockdep_on();
+        lockdep_on();
 out_restore_irqs:
-                raw_local_irq_restore(flags);
-        }
+        raw_local_irq_restore(flags);
 
         preempt_enable();
         return printed_len;