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Message-Id: <A601CC3C-4B09-4D8B-8564-558349D45815@gmail.com>
Date: Thu, 16 Jul 2015 22:29:05 +0900
From: Jungseok Lee <jungseoklee85@...il.com>
To: AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, catalin.marinas@....com,
will.deacon@....com, olof@...om.net, broonie@...nel.org,
david.griego@...aro.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/3] arm64: refactor save_stack_trace()
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@...dmis.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 */
How about binding it to -4 in unwind_frame function?
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.
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.
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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