| title: | RE kGDB Cannot compile KGDB on ARM SMP |
|
Hello,
No one has yet to submit a patch which implements the proper way to
interrupt the slave CPUs and get them to call the kgdb_nmicallback(), as
well as to run the kgdb test suite on the SMP device.
Ive done the obvious thing with this patch:
diff --git a/arch/arm/kernel/kgdb.c b/arch/arm/kernel/kgdb.c
index ba8ccfe..a5b846b 100644
--- a/arch/arm/kernel/kgdb.c
+++ b/arch/arm/kernel/kgdb.c
@@ -9,6 +9,7 @@
* Authors: George Davis <davis_g@xxxxxxxxxx
* Deepak Saxena <dsaxena@xxxxxxxxxxx
*/
+#include <linux/irq.h
#include <linux/kgdb.h
#include <asm/traps.h
@@ -158,6 +159,18 @@ static struct undef_hook kgdb_compiled_brkpt_hook = {
.fn = kgdb_compiled_brk_fn
};
+static void kgdb_call_nmi_hook(void *ignored)
+{
+ kgdb_nmicallback(raw_smp_processor_id(), get_irq_regs());
+}
+
+void kgdb_roundup_cpus(unsigned long flags)
+{
+ local_irq_enable();
+ smp_call_function(kgdb_call_nmi_hook, NULL, 0);
+ local_irq_disable();
+}
+
/**
* kgdb_arch_init - Perform any architecture specific initalization.
*
This is all well and good and solves the compilation issue. However, in an
SMP environment [quad-core ARM 11MPCore] the testsuite very quickly deadlocks:
rv-pb11mpcore:~# echo kgdbts=V1 /sys/module/kgdbts/parameters/kgdbts
[ 62.787343] kgdb: Registered I/O driver kgdbts.
[ 62.801176] kgdbts:RUN plant and detach test
[ 62.814748] kgdbts:RUN sw breakpoint test
[ 62.828126] kgdbts:RUN bad memory access test
[ 62.841687] kgdbts:RUN singlestep test 1000 iterations
[ 62.859816] kgdbts:RUN singlestep [0/1000]
[ 63.132699] kgdbts:RUN singlestep [100/1000]
[ 63.406217] kgdbts:RUN singlestep [200/1000]
[ 63.679694] kgdbts:RUN singlestep [300/1000]
<machine completely unresponsive
I took a quick look at the code in kernel/kgdb.c and adding the following
memory barrier appears to resolve the issue:
diff --git a/kernel/kgdb.c b/kernel/kgdb.c
index 761fdd2..1308381 100644
--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -1537,6 +1537,7 @@ acquirelock:
* Wait till all the CPUs have quit
* from the debugger.
*/
+ smp_wmb();
for_each_online_cpu(i) {
while (atomic_read(&cpu_in_kgdb[i]))
cpu_relax();
There may be more that are missing, but Im not familiar enough with KGDB
internals to know whats going on.
I can submit this as a patch if youd like, but Id value some feedback
first. Adding random memory barriers isnt a great solution!
Cheers,
Will
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