Re: [PATCH] powerpc/xmon: really enable xmon when a breakpoint is set
From: Vaibhav Jain <hidden>
Date: 2018-05-22 07:24:16
Also in:
lkml
Thanks for the patch Michal, Michal Suchanek [off-list ref] writes:
When single-stepping kernel code from xmon without a debug hook enabled
the kernel crashes. This can happen when kernel starts with xmon on
crash disabled but xmon is entered using sysrq.
Commit e1368d0c9edb ("powerpc/xmon: Setup debugger hooks when first
break-point is set") adds force_enable_xmon function that prints
"xmon: Enabling debugger hooks" but does not enable them.Debugger hooks are enabled just befores debugger() is entered from sysrq_handle_xmon(). Thats why force_enable_xmon() simply sets sets 'xmon_on=1' and exits. The problem you are seeing is probably due to sysrq_handle_xmon() clearing the debugger hooks on return from debugger() as xmon_on was never set for the 's' xmon command.
Add the call to xmon_init to install the debugger hooks in force_enable_xmon and also call force_enable_xmon when single-stepping in xmon.
Only calling force_enable_xmon() from do_step() should be suffice as on exit from the debugger() the value of xmon_on is checked and if required the debugger hooks are kept instead of getting cleared.
quoted hunk ↗ jump to hunk
arch/powerpc/xmon/xmon.c | 5 +++++ 1 file changed, 5 insertions(+)diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c index a0842f1ff72c..504bd1c3d8b0 100644 --- a/arch/powerpc/xmon/xmon.c +++ b/arch/powerpc/xmon/xmon.c
quoted hunk ↗ jump to hunk
@@ -1275,6 +1279,7 @@ static inline void force_enable_xmon(void) if (!xmon_on) { printf("xmon: Enabling debugger hooks\n"); xmon_on = 1; + xmon_init(1); } }
As mentioned above call to force_enable_xmon() is usually done in context of sysrq_handle_xmon() which sets the debugger hooks as soon as its entered. So I think that this hunk is not really needed. -- Vaibhav Jain [off-list ref] Linux Technology Center, IBM India Pvt. Ltd.