Messages in this thread Patch in this message | | | Subject | Re: [PATCH v4 2/2] arm64: Expand the stack trace feature to support IRQ stack | From | AKASHI Takahiro <> | Date | Thu, 15 Oct 2015 13:19:49 +0900 |
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Jungseok,
On 10/14/2015 09:55 PM, Jungseok Lee wrote: > On Oct 14, 2015, at 9:24 PM, Jungseok Lee wrote: >> On Oct 14, 2015, at 4:13 PM, AKASHI Takahiro wrote: >>> On 10/09/2015 11:24 PM, James Morse wrote: >>>> Hi Jungseok, >>>> >>>> On 07/10/15 16:28, Jungseok Lee wrote: >>>>> Currently, a call trace drops a process stack walk when a separate IRQ >>>>> stack is used. It makes a call trace information much less useful when >>>>> a system gets paniked in interrupt context. >>>> >>>> panicked >>>> >>>>> This patch addresses the issue with the following schemes: >>>>> >>>>> - Store aborted stack frame data >>>>> - Decide whether another stack walk is needed or not via current sp >>>>> - Loosen the frame pointer upper bound condition >>>> >>>> It may be worth merging this patch with its predecessor - anyone trying to >>>> bisect a problem could land between these two patches, and spend time >>>> debugging the truncated call traces. >>>> >>>> >>>>> diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h >>>>> index 6ea82e8..e5904a1 100644 >>>>> --- a/arch/arm64/include/asm/irq.h >>>>> +++ b/arch/arm64/include/asm/irq.h >>>>> @@ -2,13 +2,25 @@ >>>>> #define __ASM_IRQ_H >>>>> >>>>> #include <linux/irqchip/arm-gic-acpi.h> >>>>> +#include <asm/stacktrace.h> >>>>> >>>>> #include <asm-generic/irq.h> >>>>> >>>>> struct irq_stack { >>>>> void *stack; >>>>> + struct stackframe frame; >>>>> }; >>>>> >>>>> +DECLARE_PER_CPU(struct irq_stack, irq_stacks); >>>> >>>> Good idea, storing this in the per-cpu data makes it immune to stack >>>> corruption. >>> >>> Is this the only reason that you have a dummy stack frame in per-cpu data? >>> By placing this frame in an interrupt stack, I think, we will be able to eliminate >>> changes in dump_stace(). and >>> >>>> >>>>> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c >>>>> index 407991b..5124649 100644 >>>>> --- a/arch/arm64/kernel/stacktrace.c >>>>> +++ b/arch/arm64/kernel/stacktrace.c >>>>> @@ -43,7 +43,27 @@ int notrace unwind_frame(struct stackframe *frame) >>>>> low = frame->sp; >>>>> high = ALIGN(low, THREAD_SIZE); >>>>> >>>>> - if (fp < low || fp > high - 0x18 || fp & 0xf) >>>>> + /* >>>>> + * A frame pointer would reach an upper bound if a prologue of the >>>>> + * first function of call trace looks as follows: >>>>> + * >>>>> + * stp x29, x30, [sp,#-16]! >>>>> + * mov x29, sp >>>>> + * >>>>> + * Thus, the upper bound is (top of stack - 0x20) with consideration >>>> >>>> The terms 'top' and 'bottom' of the stack are confusing, your 'top' appears >>>> to be the highest address, which is used first, making it the bottom of the >>>> stack. >>>> >>>> I would try to use the terms low/est and high/est, in keeping with the >>>> variable names in use here. >>>> >>>> >>>>> + * of a 16-byte empty space in THREAD_START_SP. >>>>> + * >>>>> + * The value, 0x20, however, does not cover all cases as interrupts >>>>> + * are handled using a separate stack. That is, a call trace can start >>>>> + * from elx_irq exception vectors. The symbols could not be promoted >>>>> + * to candidates for a stack trace under the restriction, 0x20. >>>>> + * >>>>> + * The scenario is handled without complexity as 1) considering >>>>> + * (bottom of stack + THREAD_START_SP) as a dummy frame pointer, the >>>>> + * content of which is 0, and 2) allowing the case, which changes >>>>> + * the value to 0x10 from 0x20. >>>> >>>> Where has 0x20 come from? The old value was 0x18. >>>> >>>> My understanding is the highest part of the stack looks like this: >>>> high [ off-stack ] >>>> high - 0x08 [ left free by THREAD_START_SP ] >>>> high - 0x10 [ left free by THREAD_START_SP ] >>>> high - 0x18 [#1 x30 ] >>>> high - 0x20 [#1 x29 ] >>>> >>>> So the condition 'fp > high - 0x18' prevents returning either 'left free' >>>> address, or off-stack-value as a frame. Changing it to 'fp > high - 0x10' >>>> allows the first half of that reserved area to be a valid stack frame. >>>> >>>> This change is breaking perf using incantations [0] and [1]: >>>> >>>> Before, with just patch 1/2: >>>> ---__do_softirq >>>> | >>>> |--92.95%-- __handle_domain_irq >>>> | __irqentry_text_start >>>> | el1_irq >>>> | >>>> >>>> After, with both patches: >>>> ---__do_softirq >>>> | >>>> |--83.83%-- __handle_domain_irq >>>> | __irqentry_text_start >>>> | el1_irq >>>> | | >>>> | |--99.39%-- 0x400008040d00000c >>>> | --0.61%-- [...] >>>> | >>> >>> This also shows that walk_stackframe() doesn't walk through a process stack. >>> Now I'm trying the following hack on top of Jungseok's patch. >>> (It doesn't traverse from an irq stack to an process stack yet. I need modify >>> unwind_frame().) >> >> I've got a difference between perf and dump_backtrace() as reviewing perf call >> chain operation. Perf relies on walk_stackframe(), but dump_backtrace() does not. >> That is, a symbol is printed out *before* unwind_frame() call in case of perf. >> By contrast, dump_backtrace() records a symbol *after* unwind_frame(). I think >> perf behavior is correct since frame.pc is retrieved from a valid stack frame. >> >> So, the following diff is a prerequisite. It looks reasonable to remove dump_mem() >> call since frame.sp is calculated incorrectly now. If accepted, dump_backtrace() >> could utilize walk_stackframe(), which simplifies the code. >> >> ----8<---- >> diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c >> index f93aae5..e18be43 100644 >> --- a/arch/arm64/kernel/traps.c >> +++ b/arch/arm64/kernel/traps.c >> @@ -103,12 +103,15 @@ static void dump_mem(const char *lvl, const char *str, unsigned long bottom, >> set_fs(fs); >> } >> >> -static void dump_backtrace_entry(unsigned long where, unsigned long stack) >> +static void dump_backtrace_entry(unsigned long where) >> { >> + /* >> + * PC has a physical address when MMU is disabled. >> + */ >> + if (!kernel_text_address(where)) >> + where = (unsigned long)phys_to_virt(where); >> + >> print_ip_sym(where); >> - if (in_exception_text(where)) >> - dump_mem("", "Exception stack", stack, >> - stack + sizeof(struct pt_regs), false); >> } >> >> static void dump_instr(const char *lvl, struct pt_regs *regs) >> @@ -172,12 +175,17 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk) >> pr_emerg("Call trace:\n"); >> while (1) { >> unsigned long where = frame.pc; >> + unsigned long stack; >> int ret; >> >> + dump_backtrace_entry(where); >> ret = unwind_frame(&frame); >> if (ret < 0) >> break; >> - dump_backtrace_entry(where, frame.sp); >> + stack = frame.sp; >> + if (in_exception_text(where)) >> + dump_mem("", "Exception stack", stack, >> + stack + sizeof(struct pt_regs), false); >> } >> } >> ----8<---- >> >>> Thanks, >>> -Takahiro AKASHI >>> ----8<---- >>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S >>> index 650cc05..5fbd1ea 100644 >>> --- a/arch/arm64/kernel/entry.S >>> +++ b/arch/arm64/kernel/entry.S >>> @@ -185,14 +185,12 @@ alternative_endif >>> mov x23, sp >>> and x23, x23, #~(THREAD_SIZE - 1) >>> cmp x20, x23 // check irq re-enterance >>> + mov x19, sp >>> beq 1f >>> - str x29, [x19, #IRQ_FRAME_FP] >>> - str x21, [x19, #IRQ_FRAME_SP] >>> - str x22, [x19, #IRQ_FRAME_PC] >>> - mov x29, x24 >>> -1: mov x19, sp >>> - csel x23, x19, x24, eq // x24 = top of irq stack >>> - mov sp, x23 >>> + mov sp, x24 // x24 = top of irq stack >>> + stp x29, x22, [sp, #-32]! >>> + mov x29, sp >>> +1: >>> .endm >>> >>> /* >> >> Is it possible to decide which stack is used without aborted SP information? > > We could know which stack is used via current SP, but how could we decide > a variable 'low' in unwind_frame() when walking a process stack?
The following patch, replacing your [PATCH 2/2], seems to work nicely, traversing from interrupt stack to process stack. I tried James' method as well as "echo c > /proc/sysrq-trigger."
The only issue that I have now is that dump_backtrace() does not show correct "pt_regs" data on process stack (actually it dumps interrupt stack):
CPU1: stopping CPU: 1 PID: 0 Comm: swapper/1 Tainted: G D 4.3.0-rc5+ #24 Hardware name: ARM Arm Versatile Express/Arm Versatile Express, BIOS 11:37:19 Jul 16 2015 Call trace: [<ffffffc00008a7b0>] dump_backtrace+0x0/0x19c [<ffffffc00008a968>] show_stack+0x1c/0x28 [<ffffffc0003936d0>] dump_stack+0x88/0xc8 [<ffffffc00008fdf8>] handle_IPI+0x258/0x268 [<ffffffc000082530>] gic_handle_irq+0x88/0xa4 Exception stack(0xffffffc87b1bffa0 to 0xffffffc87b1c00c0) <== HERE ffa0: ffffffc87b18fe30 ffffffc87b1bc000 ffffffc87b18ff50 ffffffc000086ac8 ffc0: ffffffc87b18c000 afafafafafafafaf ffffffc87b18ff50 ffffffc000086ac8 ffe0: ffffffc87b18ff50 ffffffc87b18ff50 afafafafafafafaf afafafafafafafaf 0000: 0000000000000000 ffffffffffffffff ffffffc87b195c00 0000000200000002 0020: 0000000057ac6e9d afafafafafafafaf afafafafafafafaf afafafafafafafaf 0040: afafafafafafafaf afafafafafafafaf afafafafafafafaf afafafafafafafaf 0060: afafafafafafafaf afafafafafafafaf afafafafafafafaf afafafafafafafaf 0080: afafafafafafafaf afafafafafafafaf afafafafafafafaf afafafafafafafaf 00a0: afafafafafafafaf afafafafafafafaf afafafafafafafaf afafafafafafafaf [<ffffffc0000855e0>] el1_irq+0xa0/0x114 [<ffffffc000086ac4>] arch_cpu_idle+0x14/0x20 [<ffffffc0000fc110>] default_idle_call+0x1c/0x34 [<ffffffc0000fc464>] cpu_startup_entry+0x2cc/0x30c [<ffffffc00008f7c4>] secondary_start_kernel+0x120/0x148 [<ffffffc0000827a8>] secondary_startup+0x8/0x20
Thanks, -Takahiro AKASHI
----8<---- From 1aa8d4e533d44099f69ff761acfa3c1045a00796 Mon Sep 17 00:00:00 2001 From: AKASHI Takahiro <takahiro.akashi@linaro.org> Date: Thu, 15 Oct 2015 09:04:10 +0900 Subject: [PATCH] arm64: revamp unwind_frame for interrupt stack
This patch allows unwind_frame() to traverse from interrupt stack to process stack correctly by having a dummy stack frame for irq_handler created at its prologue.
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> --- arch/arm64/kernel/entry.S | 22 ++++++++++++++++++++-- arch/arm64/kernel/stacktrace.c | 14 +++++++++++++- 2 files changed, 33 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 6d4e8c5..25cabd9 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -185,8 +185,26 @@ alternative_endif and x23, x23, #~(THREAD_SIZE - 1) cmp x20, x23 // check irq re-enterance mov x19, sp - csel x23, x19, x24, eq // x24 = top of irq stack - mov sp, x23 + beq 1f + mov sp, x24 // x24 = top of irq stack + stp x29, x21, [sp, #-16]! // for sanity check + stp x29, x22, [sp, #-16]! // dummy stack frame + mov x29, sp +1: + /* + * Layout of interrupt stack after this macro is invoked: + * + * | | + *-0x20+----------------+ <= dummy stack frame + * | fp | : fp on process stack + *-0x18+----------------+ + * | lr | : return address + *-0x10+----------------+ + * | fp (copy) | : for sanity check + * -0x8+----------------+ + * | sp | : sp on process stack + * 0x0+----------------+ + */ .endm
/* diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c index 407991b..03611a1 100644 --- a/arch/arm64/kernel/stacktrace.c +++ b/arch/arm64/kernel/stacktrace.c @@ -43,12 +43,24 @@ int notrace unwind_frame(struct stackframe *frame) low = frame->sp; high = ALIGN(low, THREAD_SIZE);
- if (fp < low || fp > high - 0x18 || fp & 0xf) + if (fp < low || fp > high - 0x20 || fp & 0xf) return -EINVAL;
frame->sp = fp + 0x10; frame->fp = *(unsigned long *)(fp); /* + * check whether we are going to walk trough from interrupt stack + * to process stack + * If the previous frame is the initial (dummy) stack frame on + * interrupt stack, frame->sp now points to just below the frame + * (dummy frame + 0x10). + * See entry.S + */ +#define STACK_LOW(addr) round_down((addr), THREAD_SIZE) + if ((STACK_LOW(frame->sp) != STACK_LOW(frame->fp)) && + (frame->fp == *(unsigned long *)frame->sp)) + frame->sp = *((unsigned long *)(frame->sp + 8)); + /* * -4 here because we care about the PC at time of bl, * not where the return will go. */ -- 1.7.9.5
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