kgdb: timeout if secondary CPUs ignore the roundup

Currently if an active CPU fails to respond to a roundup request the CPU
that requested the roundup will become stuck.  This needlessly reduces the
robustness of the debugger.

This patch introduces a timeout allowing the system state to be examined
even when the system contains unresponsive processors.  It also modifies
kdb's cpu command to make it censor attempts to switch to unresponsive
processors and to report their state as (D)ead.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index 1adf62b39b96..acd749736822 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -471,6 +471,7 @@ static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
         int cpu;
         int trace_on = 0;
         int online_cpus = num_online_cpus();
+        u64 time_left;
 
         kgdb_info[ks->cpu].enter_kgdb++;
         kgdb_info[ks->cpu].exception_state |= exception_state;
@@ -595,9 +596,13 @@ return_normal:
         /*
          * Wait for the other CPUs to be notified and be waiting for us:
          */
-        while (kgdb_do_roundup && (atomic_read(&masters_in_kgdb) +
-                                atomic_read(&slaves_in_kgdb)) != online_cpus)
+        time_left = loops_per_jiffy * HZ;
+        while (kgdb_do_roundup && --time_left &&
+               (atomic_read(&masters_in_kgdb) + atomic_read(&slaves_in_kgdb)) !=
+                   online_cpus)
                 cpu_relax();
+        if (!time_left)
+                pr_crit("KGDB: Timed out waiting for secondary CPUs.\n");
 
         /*
          * At this point the primary processor is completely