debug lockups: Improve lockup detection, fix generic arch fallback

As Andrew noted, my previous patch ("debug lockups: Improve lockup
detection") broke/removed SysRq-L support from architecture that do
not provide a __trigger_all_cpu_backtrace implementation.

Restore a fallback path and clean up the SysRq-L machinery a bit:

 - Rename the arch method to arch_trigger_all_cpu_backtrace()

 - Simplify the define

 - Document the method a bit - in the hope of more architectures
   adding support for it.

[ The patch touches Sparc code for the rename. ]

Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "David S. Miller" <davem@davemloft.net>
LKML-Reference: <20090802140809.7ec4bb6b.akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 14 insertions, 1 deletions

diff --git a/drivers/char/sysrq.c b/drivers/char/sysrq.c
index 165f307f30e8..50eecfe1d724 100644
--- a/drivers/char/sysrq.c
+++ b/drivers/char/sysrq.c
@@ -223,7 +223,20 @@ static DECLARE_WORK(sysrq_showallcpus, sysrq_showregs_othercpus);
 
 static void sysrq_handle_showallcpus(int key, struct tty_struct *tty)
 {
-        trigger_all_cpu_backtrace();
+        /*
+         * Fall back to the workqueue based printing if the
+         * backtrace printing did not succeed or the
+         * architecture has no support for it:
+         */
+        if (!trigger_all_cpu_backtrace()) {
+                struct pt_regs *regs = get_irq_regs();
+
+                if (regs) {
+                        printk(KERN_INFO "CPU%d:\n", smp_processor_id());
+                        show_regs(regs);
+                }
+                schedule_work(&sysrq_showallcpus);
+        }
 }
 
 static struct sysrq_key_op sysrq_showallcpus_op = {