From af2d8289f57e427836be482c6f72cca674028121 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Sun, 6 Dec 2009 05:34:27 +0100 Subject: [PATCH] x86: Fixup wrong irq frame link in stacktraces When we enter in irq, two things can happen to preserve the link to the previous frame pointer: - If we were in an irq already, we don't switch to the irq stack as we are inside. We just need to save the previous frame pointer and to link the new one to the previous. - Otherwise we need another level of indirection. We enter the irq with the previous stack. We save the previous bp inside and make bp pointing to its saved address. Then we switch to the irq stack and push bp another time but to the new stack. This makes two levels to dereference instead of one. In the second case, the current stacktrace code omits the second level and loses the frame pointer accuracy. The stack that follows will then be considered as unreliable. Handling that makes the perf callchain happier. Before: 43.94% [k] _raw_read_lock | --- _read_lock | |--60.53%-- send_sigio | __kill_fasync | kill_fasync | evdev_pass_event | evdev_event | input_pass_event | input_handle_event | input_event | synaptics_process_byte | psmouse_handle_byte | psmouse_interrupt | serio_interrupt | i8042_interrupt | handle_IRQ_event | handle_edge_irq | handle_irq | __irqentry_text_start | ret_from_intr | | | |--30.43%-- __select | | | |--17.39%-- 0x454f15 | | | |--13.04%-- __read | | | |--13.04%-- vread_hpet | | | |--13.04%-- _xcb_lock_io | | | --13.04%-- 0x7f630878ce8 After: 50.00% [k] _raw_read_lock | --- _read_lock | |--98.97%-- send_sigio | __kill_fasync | kill_fasync | evdev_pass_event | evdev_event | input_pass_event | input_handle_event | input_event | | | |--96.88%-- synaptics_process_byte | | psmouse_handle_byte | | psmouse_interrupt | | serio_interrupt | | i8042_interrupt | | handle_IRQ_event | | handle_edge_irq | | handle_irq | | __irqentry_text_start | | ret_from_intr | | | | | |--39.78%-- __const_udelay | | | | | | | |--91.89%-- ath5k_hw_register_timeout | | | | ath5k_hw_noise_floor_calibration | | | | ath5k_hw_reset | | | | ath5k_reset | | | | ath5k_config | | | | ieee80211_hw_config | | | | | | | | | |--88.24%-- ieee80211_scan_work | | | | | worker_thread | | | | | kthread | | | | | child_rip | | | | | | | | | --11.76%-- ieee80211_scan_completed | | | | ieee80211_scan_work | | | | worker_thread | | | | kthread | | | | child_rip | | | | | | | --8.11%-- ath5k_hw_noise_floor_calibration | | | ath5k_hw_reset | | | ath5k_reset | | | ath5k_config Note: This does not only affect perf events but also x86-64 stacktraces. They were considered as unreliable once we quit the irq stack frame. Signed-off-by: Frederic Weisbecker Cc: Peter Zijlstra Cc: Paul Mackerras Cc: Arnaldo Carvalho de Melo Cc: "K. Prasad" Cc: Thomas Gleixner Cc: "H. Peter Anvin" --- arch/x86/kernel/dumpstack_64.c | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c index a071e6b..004b8aa 100644 --- a/arch/x86/kernel/dumpstack_64.c +++ b/arch/x86/kernel/dumpstack_64.c @@ -101,6 +101,35 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack, return NULL; } +static inline int +in_irq_stack(unsigned long *stack, unsigned long *irq_stack, + unsigned long *irq_stack_end) +{ + return (stack >= irq_stack && stack < irq_stack_end); +} + +/* + * We are returning from the irq stack and go to the previous one. + * If the previous stack is also in the irq stack, then bp in the first + * frame of the irq stack points to the previous, interrupted one. + * Otherwise we have another level of indirection: We first save + * the bp of the previous stack, then we switch the stack to the irq one + * and save a new bp that links to the previous one. + * (See save_args()) + */ +static inline unsigned long +fixup_bp_irq_link(unsigned long bp, unsigned long *stack, + unsigned long *irq_stack, unsigned long *irq_stack_end) +{ +#ifdef CONFIG_FRAME_POINTER + struct stack_frame *frame = (struct stack_frame *)bp; + + if (!in_irq_stack(stack, irq_stack, irq_stack_end)) + return (unsigned long)frame->next_frame; +#endif + return bp; +} + /* * x86-64 can have up to three kernel stacks: * process stack @@ -173,7 +202,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs, irq_stack = irq_stack_end - (IRQ_STACK_SIZE - 64) / sizeof(*irq_stack); - if (stack >= irq_stack && stack < irq_stack_end) { + if (in_irq_stack(stack, irq_stack, irq_stack_end)) { if (ops->stack(data, "IRQ") < 0) break; bp = print_context_stack(tinfo, stack, bp, @@ -184,6 +213,8 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs, * pointer (index -1 to end) in the IRQ stack: */ stack = (unsigned long *) (irq_stack_end[-1]); + bp = fixup_bp_irq_link(bp, stack, irq_stack, + irq_stack_end); irq_stack_end = NULL; ops->stack(data, "EOI"); continue; -- 2.7.4