kernel/printk/printk.c: revert "printk: enable interrupts before calling console_trylock_for_printk()"

Revert commit 939f04bec1a4 ("printk: enable interrupts before calling
console_trylock_for_printk()").

Andreas reported:

: None of the post 3.15 kernel boot for me. They all hang at the GRUB
: screen telling me it loaded and started the kernel, but the kernel
: itself stops before it prints anything (or even replaces the GRUB
: background graphics).

939f04bec1a4 is modest latency reduction.  Revert it until we understand
the reason for these failures.

Reported-by: Andreas Bombe <aeb@debian.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 18 insertions, 26 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ea2d5f6962ed..13e839dbca07 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1416,9 +1416,10 @@ static int have_callable_console(void)
 /*
  * 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.
+ * 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)
 {
@@ -1431,10 +1432,8 @@ static inline int can_use_console(unsigned int cpu)
  * console_lock held, and 'console_locked' set) if it
  * is successful, false otherwise.
  */
-static int console_trylock_for_printk(void)
+static int console_trylock_for_printk(unsigned int cpu)
 {
-        unsigned int cpu = smp_processor_id();
-
         if (!console_trylock())
                 return 0;
         /*
@@ -1609,8 +1608,7 @@ asmlinkage int vprintk_emit(int facility, int level,
                  */
                 if (!oops_in_progress && !lockdep_recursing(current)) {
                         recursion_bug = 1;
-                        local_irq_restore(flags);
-                        return 0;
+                        goto out_restore_irqs;
                 }
                 zap_locks();
         }
@@ -1718,27 +1716,21 @@ asmlinkage int vprintk_emit(int facility, int level,
 
         logbuf_cpu = UINT_MAX;
         raw_spin_unlock(&logbuf_lock);
-        lockdep_on();
-        local_irq_restore(flags);
 
         /* If called from the scheduler, we can not call up(). */
-        if (in_sched)
-                return printed_len;
-
-        /*
-         * Disable preemption to avoid being preempted while holding
-         * console_sem which would prevent anyone from printing to console
-         */
-        preempt_disable();
-        /*
-         * Try to acquire and then immediately release the console semaphore.
-         * The release will print out buffers and wake up /dev/kmsg and syslog()
-         * users.
-         */
-        if (console_trylock_for_printk())
-                console_unlock();
-        preempt_enable();
+        if (!in_sched) {
+                /*
+                 * Try to acquire and then immediately release the console
+                 * semaphore.  The release will print out buffers and wake up
+                 * /dev/kmsg and syslog() users.
+                 */
+                if (console_trylock_for_printk(this_cpu))
+                        console_unlock();
+        }
 
+        lockdep_on();
+out_restore_irqs:
+        local_irq_restore(flags);
         return printed_len;
 }
 EXPORT_SYMBOL(vprintk_emit);