[RFC 2/3] arm64: refactor save_stack_trace()
AKASHI Takahiro
takahiro.akashi at linaro.org
Thu Jul 16 19:04:48 PDT 2015
Jungseok,
Thank you for your testing and reviews.
On 07/16/2015 10:29 PM, Jungseok Lee wrote:
> On Jul 16, 2015, at 10:08 AM, AKASHI Takahiro wrote:
>
> Hi, AKASHI
>
>> On 07/16/2015 09:27 AM, AKASHI Takahiro wrote:
>>> On 07/16/2015 01:13 AM, Steven Rostedt wrote:
>>>> On Wed, 15 Jul 2015 10:55:36 -0400
>>>> Steven Rostedt <rostedt at goodmis.org> wrote:
>>>>
>>>>
>>>>> I'll take a look at it and try to clean up the code.
>>>>
>>>> Does the following patch make sense for you?
>>>
>>> Looks nice. The patch greatly simplifies changes on arm64 side.
>>
>> As follows:
>>
>> - Takahiro AKASHI
>>
>> diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
>> index c5534fa..868d6f1 100644
>> --- a/arch/arm64/include/asm/ftrace.h
>> +++ b/arch/arm64/include/asm/ftrace.h
>> @@ -15,6 +15,7 @@
>>
>> #define MCOUNT_ADDR ((unsigned long)_mcount)
>> #define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE
>> +#define FTRACE_STACK_FRAME_OFFSET 4 /* sync it up with stacktrace.c */
Well,
#define FTRACE_STACK_FRAME_OFFSET AARCH64_INSN_SIZE
might be better.
> How about binding it to -4 in unwind_frame function?
Do you mean like this?
In unwind_frame(),
frame->pc = *(unsigned long*)(fp + 8) - AARCH64_INSN_SIZE;
> IMHO, it would help other developers trying to change stack trace code
> be aware of this stack tracer feature.
>
>> #ifndef __ASSEMBLY__
>> #include <linux/compat.h>
>> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
>> index 1da6029..2c1bf7d 100644
>> --- a/include/linux/ftrace.h
>> +++ b/include/linux/ftrace.h
>> @@ -260,6 +260,13 @@ static inline void ftrace_kill(void) { }
>> #endif /* CONFIG_FUNCTION_TRACER */
>>
>> #ifdef CONFIG_STACK_TRACER
>> +/*
>> + * the offset value to add to return address from save_stack_trace()
>> + */
>> +#ifndef FTRACE_STACK_FRAME_OFFSET
>> +#define FTRACE_STACK_FRAME_OFFSET 0
>> +#endif
>> +
>> extern int stack_tracer_enabled;
>> int
>> stack_trace_sysctl(struct ctl_table *table, int write,
>> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
>> index 9384647..c5b9748 100644
>> --- a/kernel/trace/trace_stack.c
>> +++ b/kernel/trace/trace_stack.c
>> @@ -105,7 +105,7 @@ check_stack(unsigned long ip, unsigned long *stack)
>>
>> /* Skip over the overhead of the stack tracer itself */
>> for (i = 0; i < max_stack_trace.nr_entries; i++) {
>> - if (stack_dump_trace[i] == ip)
>> + if ((stack_dump_trace[i] + FTRACE_STACK_FRAME_OFFSET) == ip)
>> break;
>> }
>>
>> @@ -131,7 +131,8 @@ check_stack(unsigned long ip, unsigned long *stack)
>> p = start;
>>
>> for (; p < top && i < max_stack_trace.nr_entries; p++) {
>> - if (*p == stack_dump_trace[i]) {
>> + if (*p == (stack_dump_trace[i]
>> + + FTRACE_STACK_FRAME_OFFSET)) {
>> stack_dump_trace[x] = stack_dump_trace[i++];
>> this_size = stack_dump_index[x++] =
>> (top - p) * sizeof(unsigned long);
>> --
>
> I've prepared a kernel with the following patches and reviewed them.
>
> 1) Steve's clean up patch
> 2) This patch
> 3) [RFC 2/3]
>
> AFAIU, [RFC 3/3] is not needed any more thanks to Steve's patch.
We don't need [2/3].
> First of all, let's look at the following data.
>
> 1) stack_trace data
> Depth Size Location (55 entries)
> ----- ---- --------
> 0) 4808 16 notifier_call_chain+0x2c/0x94
> 1) 4792 64 raw_notifier_call_chain+0x34/0x44
> 2) 4728 48 timekeeping_update.constprop.9+0xb8/0x114
> 3) 4680 48 update_wall_time+0x408/0x6dc
> 4) 4632 128 tick_do_update_jiffies64+0xd8/0x154
> 5) 4504 80 tick_sched_do_timer+0x50/0x60
> 6) 4424 32 tick_sched_timer+0x34/0x90
> 7) 4392 48 __run_hrtimer+0x60/0x258
> 8) 4344 64 hrtimer_interrupt+0xe8/0x260
> 9) 4280 128 arch_timer_handler_virt+0x38/0x48
> 10) 4152 32 handle_percpu_devid_irq+0x84/0x188
> 11) 4120 64 generic_handle_irq+0x38/0x54
> 12) 4056 32 __handle_domain_irq+0x68/0xbc
> 13) 4024 64 gic_handle_irq+0x38/0x88
> 14) 3960 336 el1_irq+0x64/0xd8
> 15) 3624 16 netif_rx_internal+0x14/0x198
> 16) 3608 64 netif_rx+0x20/0xa4
> 17) 3544 32 loopback_xmit+0x64/0xf4
> 18) 3512 48 dev_hard_start_xmit+0x25c/0x3f8
> 19) 3464 160 __dev_queue_xmit+0x440/0x4dc
> 20) 3304 96 dev_queue_xmit_sk+0x20/0x30
> 21) 3208 32 ip_finish_output+0x1e0/0xabc
> 22) 3176 96 ip_output+0xf0/0x120
> 23) 3080 64 ip_local_out_sk+0x44/0x54
> 24) 3016 32 ip_send_skb+0x24/0xbc
> 25) 2984 48 ip_push_pending_frames+0x40/0x60
> 26) 2936 64 icmp_push_reply+0x104/0x144
> 27) 2872 96 icmp_send+0x3c0/0x3c8
> 28) 2776 192 __udp4_lib_rcv+0x5b8/0x684
> 29) 2584 96 udp_rcv+0x2c/0x3c
> 30) 2488 32 ip_local_deliver+0xa0/0x224
> 31) 2456 48 ip_rcv+0x360/0x57c
> 32) 2408 64 __netif_receive_skb_core+0x4d0/0x80c
> 33) 2344 128 __netif_receive_skb+0x24/0x84
> 34) 2216 32 process_backlog+0x9c/0x15c
> 35) 2184 80 net_rx_action+0x1ec/0x32c
> 36) 2104 160 __do_softirq+0x114/0x2f0
> 37) 1944 128 do_softirq+0x60/0x68
> 38) 1816 32 __local_bh_enable_ip+0xb0/0xd4
> 39) 1784 32 ip_finish_output+0x1f4/0xabc
> 40) 1752 96 ip_output+0xf0/0x120
> 41) 1656 64 ip_local_out_sk+0x44/0x54
> 42) 1592 32 ip_send_skb+0x24/0xbc
> 43) 1560 48 udp_send_skb+0x1b4/0x2f4
> 44) 1512 80 udp_sendmsg+0x2a8/0x7a0
> 45) 1432 272 inet_sendmsg+0xa0/0xd0
> 46) 1160 48 sock_sendmsg+0x30/0x78
> 47) 1112 32 ___sys_sendmsg+0x15c/0x26c
> 48) 1080 400 __sys_sendmmsg+0x94/0x180
> 49) 680 320 SyS_sendmmsg+0x38/0x54
> 50) 360 360 el0_svc_naked+0x20/0x28
>
> 2) stack_max_size data
> 4888
>
> The data looks odd in two points.
> 1) the number of entry
> There is a mismatch between start token and real data
>
> 2) 80-byte gap
> stack_max_size is not aligned with "Depth" field of the first entry of stack_trace.
>
> IMHO, two items are not considered in this series as digging them out.
>
> 1) skipped entries
> As x variable is introduced in Steve's patch, it is needed to track down
> how many entries are recorded in both stack_dump_trace and stack_dump_index.
>
> 2) max_stack_trace.skip value
> max_stack_trace.skip is 0 as applying Steve's patch. The above gap could be
> observed unless the value is not considered in arch code. In the above example,
> 80-byte gap is save_stack_trace function in arch/arm64/kernel/stacktrace.c.
>
> As applying the following fix, stack_trace and stack_max_size are okay.
> However, I'm not sure which code, arch or generic ftrace, should handle trace->skip.
> The latter one is responsible for it under current implementation, not Steve's change.
>
> Please correct me if I am wrong.
I will address these issues in my later replies.
Thanks,
-Takahiro AKASHI
> Best Regards
> Jungseok Lee
>
> ----8<----
>
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index 978c923..5f6f4df 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -137,7 +137,9 @@ void save_stack_trace(struct stack_trace *trace)
>
> frame.fp = (unsigned long)__builtin_frame_address(0);
> frame.sp = current_stack_pointer;
> - frame.pc = (unsigned long)save_stack_trace_tsk;
> + frame.pc = (unsigned long)save_stack_trace;
> +
> + trace->skip += 4;
>
> __save_stack_trace(&frame, trace, 0);
> }
> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index c5b9748..5635683 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -158,6 +158,9 @@ check_stack(unsigned long ip, unsigned long *stack)
> i++;
> }
>
> + /* We do not want to include skipped entries */
> + max_stack_trace.nr_entries -= (i - x);
> +
> for (; x < max_stack_trace.nr_entries; x++)
> stack_dump_trace[x] = ULONG_MAX;
>
> @@ -330,7 +333,7 @@ static int t_show(struct seq_file *m, void *v)
> seq_printf(m, " Depth Size Location"
> " (%d entries)\n"
> " ----- ---- --------\n",
> - max_stack_trace.nr_entries - 1);
> + max_stack_trace.nr_entries);
>
> if (!stack_tracer_enabled && !max_stack_size)
> print_disabled(m);
>
> ----8<----
>
> 1) stack_trace data
> Depth Size Location (47 entries)
> ----- ---- --------
> 0) 4648 16 notifier_call_chain+0x2c/0x94
> 1) 4632 64 raw_notifier_call_chain+0x34/0x44
> 2) 4568 48 timekeeping_update.constprop.9+0xb8/0x114
> 3) 4520 48 update_wall_time+0x408/0x6dc
> 4) 4472 128 tick_do_update_jiffies64+0xd8/0x154
> 5) 4344 80 tick_sched_do_timer+0x50/0x60
> 6) 4264 32 tick_sched_timer+0x34/0x90
> 7) 4232 48 __run_hrtimer+0x60/0x258
> 8) 4184 64 hrtimer_interrupt+0xe8/0x260
> 9) 4120 128 arch_timer_handler_virt+0x38/0x48
> 10) 3992 32 handle_percpu_devid_irq+0x84/0x188
> 11) 3960 64 generic_handle_irq+0x38/0x54
> 12) 3896 32 __handle_domain_irq+0x68/0xbc
> 13) 3864 64 gic_handle_irq+0x38/0x88
> 14) 3800 336 el1_irq+0x64/0xd8
> 15) 3464 48 __kmalloc_track_caller+0x40/0x2f8
> 16) 3416 16 __kmalloc_reserve.isra.46+0x44/0x9c
> 17) 3400 144 __alloc_skb+0x70/0x180
> 18) 3256 96 alloc_skb_with_frags+0x74/0x234
> 19) 3160 112 sock_alloc_send_pskb+0x1d0/0x294
> 20) 3048 160 sock_alloc_send_skb+0x44/0x54
> 21) 2888 64 __ip_append_data.isra.40+0x78c/0xb48
> 22) 2824 224 ip_append_data.part.42+0x98/0xe8
> 23) 2600 112 ip_append_data+0x68/0x7c
> 24) 2488 96 icmp_push_reply+0x7c/0x144
> 25) 2392 96 icmp_send+0x3c0/0x3c8
> 26) 2296 192 __udp4_lib_rcv+0x5b8/0x684
> 27) 2104 96 udp_rcv+0x2c/0x3c
> 28) 2008 32 ip_local_deliver+0xa0/0x224
> 29) 1976 48 ip_rcv+0x360/0x57c
> 30) 1928 64 __netif_receive_skb_core+0x4d0/0x80c
> 31) 1864 128 __netif_receive_skb+0x24/0x84
> 32) 1736 32 process_backlog+0x9c/0x15c
> 33) 1704 80 net_rx_action+0x1ec/0x32c
> 34) 1624 160 __do_softirq+0x114/0x2f0
> 35) 1464 128 do_softirq+0x60/0x68
> 36) 1336 32 __local_bh_enable_ip+0xb0/0xd4
> 37) 1304 32 ip_finish_output+0x1f4/0xabc
> 38) 1272 96 ip_output+0xf0/0x120
> 39) 1176 64 ip_local_out_sk+0x44/0x54
> 40) 1112 32 ip_send_skb+0x24/0xbc
> 41) 1080 48 udp_send_skb+0x1b4/0x2f4
> 42) 1032 80 udp_sendmsg+0x2a8/0x7a0
> 43) 952 272 inet_sendmsg+0xa0/0xd0
> 44) 680 48 sock_sendmsg+0x30/0x78
> 45) 632 32 SyS_sendto+0xc4/0x108
> 46) 600 600 el0_svc_naked+0x20/0x28
>
> 2) stack_max_size data
> 4648
>
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