Re: [PATCH 1/2] bt: x64: filter out idle task stack

Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> · Thu, 19 May 2022 20:47:30 +0800

On 2022/5/19 3:23 PM, HAGIO KAZUHITO(萩尾 一仁) wrote:
On 2022/05/13 16:03, Qi Zheng wrote:
When we use crash to troubleshoot softlockup and other problems,
we often use the 'bt -a' command to print the stacks of running
processes on all CPUs. But now some servers have hundreds of CPUs
(such as AMD machines), which causes the 'bt -a' command to output
a lot of process stacks. And many of these stacks are the stacks
of the idle process, which are not needed by us.

Therefore, in order to reduce this part of the interference information,
this patch adds the -n parameter to the bt command. When we specify
'-n idle' (meaning no idle), the stack of the idle process will be
filtered out, thus speeding up our troubleshooting.

Good, I think that the option will be sometimes useful and the code
looks good to me.

Could you add a help text?

Sure, I can do it.


And I think that the option works only for dumpfiles captured by kdump,
in other words, does not work for qemu live dumps, ramdumps etc.  So
could you mention it in the help text and commit log?

Yes, this option works only for dumpfiles (like 'bt -a'). And I will
mention it in the help text and commit log, and send the patch v2.

Thanks,
Qi


Thanks,
Kazu


The command output is as follows:
crash> bt -a -n idle
[...]
PID: 0      TASK: ffff889ff93f5a00  CPU: 5   COMMAND: "swapper/5"

PID: 0      TASK: ffff889ff93f0000  CPU: 6   COMMAND: "swapper/6"

PID: 0      TASK: ffff889ff8c30000  CPU: 7   COMMAND: "swapper/7"

PID: 0      TASK: ffff889ff8c34380  CPU: 8   COMMAND: "swapper/8"

PID: 0      TASK: ffff889ff8c32d00  CPU: 9   COMMAND: "swapper/9"

PID: 0      TASK: ffff889ff8c31680  CPU: 10  COMMAND: "swapper/10"

PID: 0      TASK: ffff889ff8c35a00  CPU: 11  COMMAND: "swapper/11"

PID: 0      TASK: ffff889ff8c3c380  CPU: 12  COMMAND: "swapper/12"

PID: 150773  TASK: ffff889fe85a1680  CPU: 13  COMMAND: "bash"
   #0 [ffffc9000d35bcd0] machine_kexec at ffffffff8105a407
   #1 [ffffc9000d35bd28] __crash_kexec at ffffffff8113033d
   #2 [ffffc9000d35bdf0] panic at ffffffff81081930
   #3 [ffffc9000d35be70] sysrq_handle_crash at ffffffff814e38d1
   #4 [ffffc9000d35be78] __handle_sysrq.cold.12 at ffffffff814e4175
   #5 [ffffc9000d35bea8] write_sysrq_trigger at ffffffff814e404b
   #6 [ffffc9000d35beb8] proc_reg_write at ffffffff81330d86
   #7 [ffffc9000d35bed0] vfs_write at ffffffff812a72d5
   #8 [ffffc9000d35bf00] ksys_write at ffffffff812a7579
   #9 [ffffc9000d35bf38] do_syscall_64 at ffffffff81004259
      RIP: 00007fa7abcdc274  RSP: 00007fffa731f678  RFLAGS: 00000246
      RAX: ffffffffffffffda  RBX: 0000000000000002  RCX: 00007fa7abcdc274
      RDX: 0000000000000002  RSI: 0000563ca51ee6d0  RDI: 0000000000000001
      RBP: 0000563ca51ee6d0   R8: 000000000000000a   R9: 00007fa7abd6be80
      R10: 000000000000000a  R11: 0000000000000246  R12: 00007fa7abdad760
      R13: 0000000000000002  R14: 00007fa7abda8760  R15: 0000000000000002
      ORIG_RAX: 0000000000000001  CS: 0033  SS: 002b
[...]

Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
   defs.h   |  1 +
   kernel.c | 11 ++++++++++-
   x86_64.c |  8 ++++++++
   3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/defs.h b/defs.h
index a6735d0..96a7429 100644
--- a/defs.h
+++ b/defs.h
@@ -5830,6 +5830,7 @@ ulong cpu_map_addr(const char *type);
   #define BT_SHOW_ALL_REGS  (0x2000000000000ULL)
   #define BT_REGS_NOT_FOUND (0x4000000000000ULL)
   #define BT_OVERFLOW_STACK (0x8000000000000ULL)
+#define BT_SKIP_IDLE     (0x10000000000000ULL)
   #define BT_SYMBOL_OFFSET   (BT_SYMBOLIC_ARGS)
   
   #define BT_REF_HEXVAL         (0x1)
diff --git a/kernel.c b/kernel.c
index d0921cf..acfacaf 100644
--- a/kernel.c
+++ b/kernel.c
@@ -2503,7 +2503,7 @@ cmd_bt(void)
   	if (kt->flags & USE_OPT_BT)
   		bt->flags |= BT_OPT_BACK_TRACE;
   
-	while ((c = getopt(argcnt, args, "D:fFI:S:c:aAloreEgstTdxR:Ovp")) != EOF) {
+	while ((c = getopt(argcnt, args, "D:fFI:S:c:n:aAloreEgstTdxR:Ovp")) != EOF) {
                   switch (c)
   		{
   		case 'f':
@@ -2672,6 +2672,11 @@ cmd_bt(void)
   			active++;
   			break;
   
+		case 'n':
+			if (machine_type("X86_64") && STREQ(optarg, "idle"))
+				bt->flags |= BT_SKIP_IDLE;
+			break;
+
   		case 'r':
   			bt->flags |= BT_RAW;
   			break;
@@ -3092,6 +3097,10 @@ back_trace(struct bt_info *bt)
   	} else
                   machdep->get_stack_frame(bt, &eip, &esp);
   
+	/* skip idle task stack */
+	if (bt->flags & BT_SKIP_IDLE)
+		return;
+
   	if (bt->flags & BT_KSTACKP) {
   		bt->stkptr = esp;
   		return;
diff --git a/x86_64.c b/x86_64.c
index ecaefd2..cfafbcc 100644
--- a/x86_64.c
+++ b/x86_64.c
@@ -4918,6 +4918,9 @@ x86_64_get_stack_frame(struct bt_info *bt, ulong *pcp, ulong *spp)
   	if (bt->flags & BT_DUMPFILE_SEARCH)
   		return x86_64_get_dumpfile_stack_frame(bt, pcp, spp);
   
+	if (bt->flags & BT_SKIP_IDLE)
+		bt->flags &= ~BT_SKIP_IDLE;
+
           if (pcp)
                   *pcp = x86_64_get_pc(bt);
           if (spp)
@@ -4960,6 +4963,9 @@ x86_64_get_dumpfile_stack_frame(struct bt_info *bt_in, ulong *rip, ulong *rsp)
   	estack = -1;
   	panic = FALSE;
   
+	if (bt_in->flags & BT_SKIP_IDLE)
+		bt_in->flags &= ~BT_SKIP_IDLE;
+
   	panic_task = tt->panic_task == bt->task ? TRUE : FALSE;
   
   	if (panic_task && bt->machdep) {
@@ -5098,6 +5104,8 @@ next_sysrq:
                   if (!panic_task && STREQ(sym, "crash_nmi_callback")) {
                           *rip = *up;
                           *rsp = bt->stackbase + ((char *)(up) - bt->stackbuf);
+			if ((bt->flags & BT_SKIP_IDLE) && is_idle_thread(bt->task))
+				bt_in->flags |= BT_SKIP_IDLE;
                           return;
                   }
   

--
Thanks,
Qi

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