[Crash-utility] Re: [PATCH] bugfix map cpus register

Hi lianbo & guanyou, On Thu, Nov 21, 2024 at 8:56 PM Guanyou Chen <chenguanyou9338(a)gmail.com&gt; wrote: > > Hi Tao > > > 1. What is the root cause, why cpu offline state will lead to mapping > > errors? You didn't make this clear in your commit message. > > The back CPU context wrong order When the front CPU is offline. > exp: > CPU0, CPU1 is offline, CPU2 is online, CPU2's nt_prstatus_percpu from corefile note prstatus[0], because i, j not equal. > > > 2. Is this issue cpu arch specific? Since the example you gave is only > > arm64 specific, however the code change is generic for all archs. So > > I'm a bit worried about whether it will make the result incorrect for > > other archs. In addition, I didn't reproduce the mapping error issue > > on my x86_64 machine, so I cannot verify the patch locally. > > N/A > > > What command line you trigger will get the following outputs? > $ crash vmlinux vmcore -d 1 > crash> help -r > > Thanks, > Guanyou > > Tao Liu <ltao(a)redhat.com&gt; 于2024年11月21日周四 13:42写道： >> >> Hi Guanyou, >> >> Thanks for the fix. However I have a few questions for this patch: >> >> On Fri, Nov 1, 2024 at 10:16 PM Guanyou Chen <chenguanyou9338(a)gmail.com&gt; wrote: >> > >> > Hi Lianbo, Tao >> > >> > When CPUs are in an offline state, it can lead to mapping errors. >> >> 1. What is the root cause, why cpu offline state will lead to mapping >> errors? You didn't make this clear in your commit message. >> 2. Is this issue cpu arch specific? Since the example you gave is only >> arm64 specific, however the code change is generic for all archs. So >> I'm a bit worried about whether it will make the result incorrect for >> other archs. In addition, I didn't reproduce the mapping error issue >> on my x86_64 machine, so I cannot verify the patch locally. >> >> > We need to map them to the correct positions one by one. >> > >> >> 3. Please make the commit log tidy. I know you want to diff the >> outputs of "before" and "after", but we only need the info which are >> highly related to this issue. e.g: >> >> > Before: >> >> What command line you trigger will get the following outputs? >> >> > n_namesz: 5 ("CPU2") >> > n_descsz: 392 >> > n_type: 1 (NT_PRSTATUS) >> > si.signo: 0 si.code: 0 si.errno: 0 >> > cursig: 0 sigpend: 0 sighold: 0 >> > pid: 3 ppid: 0 pgrp: 0 sid:0 >> > utime: 0.000000 stime: 0.000000 >> > cutime: 0.000000 cstime: 0.000000 >> >> I'm not sure if the above info is related to this issue? >> >> > X0: ffffffc000fc8818 X1: 0000000000000000 X2: ffffffc000fc84c8 >> > X3: 0000000000000000 X4: ffffffc0405e37bf X5: ffffffc00a07372f >> > X6: 322e34323320205b X7: 545b5d3539383334 X8: ffffffc000fc2f0c >> > X9: 89fece0a9ef8cb00 X10: c0000001001f75f4 X11: 00000001001f75f4 >> > X12: 0000000000000003 X13: 00000000000005f4 X14: ffffffc009eb1210 >> > X15: 0000000000000004 X16: 000000002a4cec24 X17: 000000002a4cec24 >> > X18: ffffffc009e7d140 X19: ffffffc00a04c670 X20: 0000000000000000 >> > X21: 0000000000000000 X22: ffffff8027f22280 X23: 0000000000000009 >> > X24: 0000000000000007 X25: ffffffc009f839c0 X26: ffffffc0090f87f8 >> > X27: 0000000000000000 X28: ffffff80454f3840 X29: ffffffc0405e3b60 >> > LR: ffffffc0080e57fc SP: ffffffc0405e3b60 PC: ffffffc000fc2f84 >> >> We don't need a list of all regs, a few lines of which can indicate >> the output mismatch for "Before" and "After" is enough. >> >> > >> > CPU 0: [OFFLINE] >> > CPU 1: [OFFLINE] >> > CPU 2: >> > X0: 0000000000000000 X1: 0000000000000000 X2: 0000000000000000 >> > X3: 000000000003fcbc X4: 0000000000000001 X5: 0000000000000000 >> > X6: 0000000000000000 X7: 0000000000000000 X8: 00000000ffffffff >> > X9: ffffffc009e6ae48 X10: ffffffc009e6ae20 X11: 0000000000000000 >> > X12: 0000000000000002 X13: 0000000000000004 X14: 0000000000000000 >> > X15: 0000000000004000 X16: 00000000f90f05f6 X17: 00000000f90f05f6 >> > X18: 0000000000000000 X19: 0000000000000002 X20: ffffffc009e3b008 >> > X21: ffffffc00a01d020 X22: ffffffc009f798f0 X23: 0000000060001000 >> > X24: 0000000000000000 X25: 0000000000000000 X26: 0000000000000000 >> > X27: 0000000000000000 X28: ffffff8111eecb00 X29: ffffffc008003f50 >> > LR: ffffffc00802df88 SP: ffffffc008003f40 PC: ffffffc00802df94 >> > PSTATE: 024003c5 FPVALID: 00000000 >> > >> > After: >> > CPU 2: >> > X0: ffffffc000fc8818 X1: 0000000000000000 X2: ffffffc000fc84c8 >> > X3: 0000000000000000 X4: ffffffc0405e37bf X5: ffffffc00a07372f >> > X6: 322e34323320205b X7: 545b5d3539383334 X8: ffffffc000fc2f0c >> > X9: 89fece0a9ef8cb00 X10: c0000001001f75f4 X11: 00000001001f75f4 >> > X12: 0000000000000003 X13: 00000000000005f4 X14: ffffffc009eb1210 >> > X15: 0000000000000004 X16: 000000002a4cec24 X17: 000000002a4cec24 >> > X18: ffffffc009e7d140 X19: ffffffc00a04c670 X20: 0000000000000000 >> > X21: 0000000000000000 X22: ffffff8027f22280 X23: 0000000000000009 >> > X24: 0000000000000007 X25: ffffffc009f839c0 X26: ffffffc0090f87f8 >> > X27: 0000000000000000 X28: ffffff80454f3840 X29: ffffffc0405e3b60 >> >> > LR: ffffffc0080e57fc SP: ffffffc0405e3b60 PC: ffffffc000fc2f84 >> > PSTATE: 600000c5 FPVALID: 00000000 >> > >> > crash> bt >> > PID: 15959 TASK: ffffff80454f3840 CPU: 2 COMMAND: "AnrConsumer" >> > [ffffffc0405e3b60] ipanic at ffffffc000fc2f80 [mrdump] >> > [ffffffc0405e3b70] atomic_notifier_call_chain at ffffffc0080e57f8 >> > [ffffffc0405e3c30] panic at ffffffc008f734d0 >> > [ffffffc0405e3c80] sysrq_handle_crash at ffffffc0087f3c18 >> > [ffffffc0405e3c90] __handle_sysrq at ffffffc0087f3798 >> > [ffffffc0405e3ce0] write_sysrq_trigger at ffffffc0087f49c0 >> > [ffffffc0405e3d00] proc_reg_write at ffffffc00842e4b8 >> > [ffffffc0405e3d80] vfs_write at ffffffc008381eb4 >> > [ffffffc0405e3dd0] ksys_write at ffffffc008382200 >> > [ffffffc0405e3e10] __arm64_sys_write at ffffffc00838228c >> > [ffffffc0405e3e20] invoke_syscall at ffffffc00802efe0 >> > [ffffffc0405e3e40] el0_svc_common at ffffffc00802eef4 >> > [ffffffc0405e3e70] do_el0_svc at ffffffc00802ede8 >> > [ffffffc0405e3e80] el0_svc at ffffffc008f7a7d0 >> > [ffffffc0405e3ea0] el0t_64_sync_handler at ffffffc008f7a758 >> > [ffffffc0405e3fe0] el0t_64_sync at ffffffc00801157c >> >> The stacktrace is meaningless for this patch, we can cut this off. >> >> > PC: 00000077c798ca28 LR: 00000077a82e19f4 SP: 000000761c517af0 >> > X29: 000000761c517b00 X28: 000000761c517db8 X27: 000000761c517c90 >> > X26: 000000761c517c98 X25: 000000761c517bf9 X24: 000000761c519000 >> > X23: 000000761c517be1 X22: 0000000000000001 X21: 00000000000003e3 >> > X20: 000000761c517c11 X19: 000000761c517bf8 X18: 0000007568224000 >> > X17: 00000077c798ca20 X16: 00000077c79b2ae0 X15: b4000077202cc480 >> > X14: 0000000000000000 X13: 000000761c517a70 X12: ffffff80ffffffd0 >> > X11: 000000761c517a40 X10: 0000000000000001 X9: 0000000000000000 >> > X8: 0000000000000040 X7: 7f7f7f7f7f7f7f7f X6: 0000000000000010 >> > X5: 000000761c517c0c X4: ffffffffffffffff X3: ffffffffffffffff >> > X2: 0000000000000001 X1: 000000761c517c11 X0: 00000000000003e3 >> > ORIG_X0: 00000000000003e3 SYSCALLNO: 40 PSTATE: 00001000 >> > >> ditto. >> >> Maybe a short summary after the output paste, telling us which info >> should reviewers pay attention to. >> >> Thanks, >> Tao Liu >> >> > Signed-off-by: Guanyou.Chen <chenguanyou(a)xiaomi.com&gt; >> > --- >> > netdump.c | 6 +++--- >> > 1 file changed, 3 insertions(+), 3 deletions(-) >> > >> > diff --git a/netdump.c b/netdump.c >> > index b4e2a5c..8ea5159 100644 >> > --- a/netdump.c >> > +++ b/netdump.c >> > @@ -75,7 +75,7 @@ void >> > map_cpus_to_prstatus(void) >> > { >> > void **nt_ptr; >> > - int online, i, j, nrcpus; >> > + int online, i, nrcpus; >> > size_t size; >> > >> > if (pc->flags2 & QEMU_MEM_DUMP_ELF) /* notes exist for all cpus */ >> > @@ -100,9 +100,9 @@ map_cpus_to_prstatus(void) >> > */ >> > nrcpus = (kt->kernel_NR_CPUS ? kt->kernel_NR_CPUS : NR_CPUS); >> > >> > - for (i = 0, j = 0; i < nrcpus; i++) { >> > + for (i = 0; i < nrcpus; i++) { >> > if (in_cpu_map(ONLINE_MAP, i) && machdep->is_cpu_prstatus_valid(i)) { >> > - nd->nt_prstatus_percpu[i] = nt_ptr[j++]; >> > + nd->nt_prstatus_percpu[i] = nt_ptr[i]; I re-think about the code change, it seems to me the variable 'j' doesn't make any sense here. nt_ptr = (void **)GETBUF(size); BCOPY(nd->nt_prstatus_percpu, nt_ptr, size); BZERO(nd->nt_prstatus_percpu, size); The data of nt_ptr buffer is copied from nd->nt_prstatus_percpu buffer, then nd->nt_prstatus_percpu buffer is cleared. If cpu 0 1 2 4 is online and 3 is offline, nd->nt_prstatus_percpu[4] = nt_ptr[3]; that is, copy the original cpu3's info into current cpu4's buf. This cpu shift operation doesn't make any sense to me, nd->nt_prstatus_percpu[4] = nt_ptr[4] should make sense in this case. By searching the code, I didn't see nd->nt_prstatus_percpu[cpu] except for any cpu shifts. However I cannot find out the git history of why variable 'j' was introduced. So this patch looks correct to me, though I haven't run the overall regression test against it. What's your opinion on the variable 'j'? In addition, I can do a regression test if needed. @Lianbo Jiang

updated as well.

Thanks, Tao Liu >> > nd->num_prstatus_notes = >> > MAX(nd->num_prstatus_notes, i+1); >> > } >> > -- >> > 2.34.1 >> > >> > Guanyou. >> > Thanks. >>