Re: [Crash-utility] [PATCH v2 1/2] bt: x86_64: filter out idle task stack

Hi Qi, thanks for the update. On 2022/05/19 22:48, 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 option 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. > > And like option '-a' of bt, option '-n idle' works only for dumpfiles > captured by kdump. It's a bit different from '-a', will change to: And the option works only for crash dumps captured by kdump. because '-a' works for live dumps but '-n idle' doesn't work like this:

crash> bt -a -n idle PID: 0 TASK: ffffffff82212780 CPU: 0 COMMAND: "swapper/0" [exception RIP: native_safe_halt+2] RIP: ffffffff81820c92 RSP: ffffffff82203e90 RFLAGS: 00000246 RAX: ffffffff818209c0 RBX: 0000000000000000 RCX: 0000000000000001 RDX: 0000000000000001 RSI: 0000000000000087 RDI: 0000000000000000 RBP: 0000000000000000 R8: 00007584cc726bcd R9: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000 R13: 0000000000000000 R14: 000000007f46e168 R15: 000000007ff922a0 CS: 0010 SS: 0018 #0 [ffffffff82203e90] default_idle at ffffffff818209da #1 [ffffffff82203eb0] do_idle at ffffffff810de691 #2 [ffffffff82203ef0] cpu_startup_entry at ffffffff810de8ff #3 [ffffffff82203f10] start_kernel at ffffffff827821eb #4 [ffffffff82203f50] secondary_startup_64 at ffffffff810000e7 ... And with the following patch, Acked-by: Kazuhito Hagio <k-hagio-ab(a)nec.com&gt;

--- a/help.c +++ b/help.c @@ -1909,7 +1909,7 @@ char *help_bt[] = { "bt", "backtrace", "[-a|-c cpu(s)|-g|-r|-t|-T|-l|-e|-E|-f|-F|-o|-O|-v|-p] [-R ref] [-s [-x|d]]" -"\n [-I ip] [-S sp] [pid | task]", +"\n [-I ip] [-S sp] [-n idle] [pid | task]", " Display a kernel stack backtrace. If no arguments are given, the stack", " trace of the current context will be displayed.\n", " -a displays the stack traces of the active task on each CPU.", No need to repost, we can fix these when merging.

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(a)bytedance.com&gt; > --- > defs.h | 1 + > help.c | 30 ++++++++++++++++++++++++++++++ > kernel.c | 11 ++++++++++- > x86_64.c | 8 ++++++++ > 4 files changed, 49 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/help.c b/help.c > index 51a0fe3..6d8dc4f 100644 > --- a/help.c > +++ b/help.c > @@ -1915,6 +1915,8 @@ char *help_bt[] = { > " -a displays the stack traces of the active task on each CPU.", > " (only applicable to crash dumps)", > " -A same as -a, but also displays vector registers (S390X only).", > +" -n idle filter the stack of idle tasks (x86_64).", > +" (only applicable to crash dumps)", > " -p display the stack trace of the panic task only.", > " (only applicable to crash dumps)", > " -c cpu display the stack trace of the active task on one or more CPUs,", > @@ -2004,6 +2006,34 @@ char *help_bt[] = { > " DS: 002b ESI: bfffc8a0 ES: 002b EDI: 00000000 ", > " SS: 002b ESP: bfffc82c EBP: bfffd224 ", > " CS: 0023 EIP: 400d032e ERR: 0000008e EFLAGS: 00000246 ", > +" ", > +" Display the stack trace of the active task(s) when the kernel panicked,", > +" and filter out the stack of the idle tasks:", > +" %s> bt -a -n idle", > +" [...]", > +" 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", > +" [...]", > "\n Display the stack trace of the active task on CPU 0 and 1:\n", > " %s> bt -c 0,1", > " PID: 0 TASK: ffffffff81a8d020 CPU: 0 COMMAND: \"swapper\"", > 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; > } >