From mboxrd@z Thu Jan 1 00:00:00 1970 From: james.morse@arm.com (James Morse) Date: Fri, 02 Sep 2016 11:50:15 +0100 Subject: [PATCH V2] arm64:ftrace: add save_stack_trace_regs() In-Reply-To: <4f7d7a6bff7f06f814bf9a2bdc90bb0e3b833b66.1472734699.git.panand@redhat.com> References: <4f7d7a6bff7f06f814bf9a2bdc90bb0e3b833b66.1472734699.git.panand@redhat.com> Message-ID: <57C95967.9030308@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Pratyush, On 01/09/16 14:35, Pratyush Anand wrote: > Implement save_stack_trace_regs, so that stacktrace of a kprobe events can be > obtained. Hmm, kconfig enables 'CONFIG_KPROBE_EVENT' if we select KPROBES and FTRACE, this calls save_stack_trace_regs(), which we haven't implemented, giving: [ 373.406982] save_stack_trace_regs() not implemented yet. [ 373.413020] ------------[ cut here ]------------ [ 373.417601] WARNING: CPU: 1 PID: 0 at ../kernel/stacktrace.c:74 save_stack_tr ace_regs+0x3c/0x48 [ 373.426212] Modules linked in: [ 373.429238] [ 373.430716] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.8.0-rc4-dirty #5128 [ 373.437606] Hardware name: ARM Juno development board (r1) (DT) [ 373.443466] task: ffff800975dd1900 task.stack: ffff800975ddc000 [ 373.449327] PC is at save_stack_trace_regs+0x3c/0x48 [ 373.454242] LR is at save_stack_trace_regs+0x3c/0x48 [ 373.459156] pc : [] lr : [] pstate: 600003c5 [ 373.466476] sp : ffff80097ef52c00 [ 373.554836] Call trace: [ 373.641153] [] save_stack_trace_regs+0x3c/0x48 [ 373.647104] [] __ftrace_trace_stack+0x168/0x208 [ 373.653138] [] trace_buffer_unlock_commit_regs+0x5c/0x7c [ 373.659946] [] kprobe_trace_func+0x308/0x3d8 [ 373.665721] [] kprobe_dispatcher+0x58/0x60 [ 373.671327] [] kprobe_breakpoint_handler+0xbc/0x18c [ 373.677705] [] brk_handler+0x50/0x90 [ 373.682792] [] do_debug_exception+0x50/0xbc I guess hitting a WARN_ONCE() while using a 'kernel hacking' feature isn't serious enough to make this a fix. > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c > index d9751a4769e7..bd6d9d8087f0 100644 > --- a/arch/arm64/kernel/stacktrace.c > +++ b/arch/arm64/kernel/stacktrace.c > @@ -152,6 +152,24 @@ static int save_trace(struct stackframe *frame, void *d) > return trace->nr_entries >= trace->max_entries; > } > > +void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace) > +{ > + struct stack_trace_data data; > + struct stackframe frame; > + > + data.trace = trace; > + data.skip = trace->skip; > + data.no_sched_functions = 0; > + > + frame.fp = regs->regs[29]; > + frame.sp = regs->sp; > + frame.pc = regs->pc; What happens when a kprobe-event runs over a frame the function graph tracer has meddled with? You need: #ifdef CONFIG_FUNCTION_GRAPH_TRACER frame.graph = current->curr_ret_stack; #endif > + > + walk_stackframe(current, &frame, save_trace, &data); > + if (trace->nr_entries < trace->max_entries) > + trace->entries[trace->nr_entries++] = ULONG_MAX; > +} > + > void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace) > { > struct stack_trace_data data; > Reviewed-by: James Morse Thanks, James