From 8097551d9ab9b9e3630694ad1bc6e12c597c515e Mon Sep 17 00:00:00 2001
From: Jason Wessel <jason.wessel@windriver.com>
Date: Fri, 11 Dec 2009 08:43:18 -0600
Subject: [PATCH] kgdb,x86: do not set kgdb_single_step on x86
On an SMP system the kgdb_single_step flag has the possibility to
indefinitely hang the system in the case. Consider the case where,
CPU 1 has the schedule lock and CPU 0 is set to single step, there is
no way for CPU 0 to run another task.
The easy way to observe the problem is to make 2 cpus busy, and run
the kgdb test suite. You will see that it hangs the system very
quickly.
while [ 1 ] ; do find /proc > /dev/null 2>&1 ; done &
while [ 1 ] ; do find /proc > /dev/null 2>&1 ; done &
echo V1 > /sys/module/kgdbts/parameters/kgdbts
The side effect of this patch is that there is the possibility
to miss a breakpoint in the case that a single step operation
was executed to step over a breakpoint in common code.
The trade off of the missed breakpoint is preferred to
hanging the kernel. This can be fixed in the future by
using kprobes or another strategy to step over planted
breakpoints with out of line execution.
CC: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
arch/x86/kernel/kgdb.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index aefae46aa6464..dd74fe7273b12 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -400,7 +400,6 @@ int kgdb_arch_handle_exception(int e_vector, int signo, int err_code,
/* set the trace bit if we're stepping */
if (remcomInBuffer[0] == 's') {
linux_regs->flags |= X86_EFLAGS_TF;
- kgdb_single_step = 1;
atomic_set(&kgdb_cpu_doing_single_step,
raw_smp_processor_id());
}
--
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