On Sun, 29 Jun 2014 00:50:50 +0200 Andreas Bombe <a...@debian.org> wrote:
> 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).
>
> I bisected it down to 939f04bec1a4ef6ba4370b0f34b01decc844b1b1 "printk:
> enable interrupts before calling console_trylock_for_printk()".
> Reverting that patch on the latest kernel (git 24b414d5a7) allows me to
> boot normally.
OK, thanks, I queued the below reversion. I'll hold off for a week or
two in case we come up with a fix.
> I fixed the conflict in the revert by leaving in the "if
> (in_sched) return printed_len;".
hm, that might have been buggy - we still need to the lockdep_on() and
local_irq_restore(). You're a victim of
someone-stuck-a-random-return-in-the-middle-of-a-function.
Please review this and if possible, run-time test it? Against current
mainline.
From: Andrew Morton <a...@linux-foundation.org>
Subject: kernel/printk/printk.c: revert "printk: enable interrupts before
calling console_trylock_for_printk()"
Revert 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 <a...@debian.org>
Cc: Jan Kara <j...@suse.cz>
Cc: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
---
kernel/printk/printk.c | 44 +++++++++++++++------------------------
1 file changed, 18 insertions(+), 26 deletions(-)
diff -puN
kernel/printk/printk.c~kernel-printk-printkc-revert-printk-enable-interrupts-before-calling-console_trylock_for_printk
kernel/printk/printk.c
---
a/kernel/printk/printk.c~kernel-printk-printkc-revert-printk-enable-interrupts-before-calling-console_trylock_for_printk
+++ a/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(unsign
* 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
*/
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
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);
_
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
