linux-kernel - Re: [PATCH v2] KVM: X86: Fix softlockup when get the current kvmclock timestamp

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Date:   Sat, 25 Nov 2017 11:14:53 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v2] KVM: X86: Fix softlockup when get the current
 kvmclock timestamp

Hi,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on kvm/linux-next]
[also build test WARNING on v4.14 next-20171124]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Wanpeng-Li/KVM-X86-Fix-softlockup-when-get-the-current-kvmclock-timestamp/20171109-030841
base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git linux-next
config: i386-allyesconfig (attached as .config)
compiler: gcc-7 (Debian 7.2.0-12) 7.2.1 20171025
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   In file included from arch/x86/kvm/x86.h:7:0,
                    from arch/x86/kvm/x86.c:28:
   arch/x86/kvm/x86.c: In function 'get_kvmclock_ns':
>> arch/x86/include/asm/pvclock.h:93:15: warning: '*((void *)&hv_clock+28)' may be used uninitialized in this function [-Wmaybe-uninitialized]
     u64 offset = pvclock_scale_delta(delta, src->tsc_to_system_mul,
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
              src->tsc_shift);
              ~~~~~~~~~~~~~~~
   arch/x86/kvm/x86.c:1785:32: note: '*((void *)&hv_clock+28)' was declared here
     struct pvclock_vcpu_time_info hv_clock;
                                   ^~~~~~~~
   In file included from arch/x86/kvm/x86.h:7:0,
                    from arch/x86/kvm/x86.c:28:
   arch/x86/include/asm/pvclock.h:65:2: warning: '*((void *)&hv_clock+24)' may be used uninitialized in this function [-Wmaybe-uninitialized]
     __asm__ (
     ^~~~~~~
   arch/x86/kvm/x86.c:1785:32: note: '*((void *)&hv_clock+24)' was declared here
     struct pvclock_vcpu_time_info hv_clock;
                                   ^~~~~~~~
--
   In file included from arch/x86//kvm/x86.h:7:0,
                    from arch/x86//kvm/x86.c:28:
   arch/x86//kvm/x86.c: In function 'get_kvmclock_ns':
>> arch/x86/include/asm/pvclock.h:93:15: warning: '*((void *)&hv_clock+28)' may be used uninitialized in this function [-Wmaybe-uninitialized]
     u64 offset = pvclock_scale_delta(delta, src->tsc_to_system_mul,
                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
              src->tsc_shift);
              ~~~~~~~~~~~~~~~
   arch/x86//kvm/x86.c:1785:32: note: '*((void *)&hv_clock+28)' was declared here
     struct pvclock_vcpu_time_info hv_clock;
                                   ^~~~~~~~
   In file included from arch/x86//kvm/x86.h:7:0,
                    from arch/x86//kvm/x86.c:28:
   arch/x86/include/asm/pvclock.h:65:2: warning: '*((void *)&hv_clock+24)' may be used uninitialized in this function [-Wmaybe-uninitialized]
     __asm__ (
     ^~~~~~~
   arch/x86//kvm/x86.c:1785:32: note: '*((void *)&hv_clock+24)' was declared here
     struct pvclock_vcpu_time_info hv_clock;
                                   ^~~~~~~~

vim +93 arch/x86/include/asm/pvclock.h

347bb4448 Zachary Amsden  2010-08-19  88  
dce2db0a3 Marcelo Tosatti 2012-11-27  89  static __always_inline
a5a1d1c29 Thomas Gleixner 2016-12-21  90  u64 __pvclock_read_cycles(const struct pvclock_vcpu_time_info *src, u64 tsc)
dce2db0a3 Marcelo Tosatti 2012-11-27  91  {
108b249c4 Paolo Bonzini   2016-09-01  92  	u64 delta = tsc - src->tsc_timestamp;
a5a1d1c29 Thomas Gleixner 2016-12-21 @93  	u64 offset = pvclock_scale_delta(delta, src->tsc_to_system_mul,
f7550d076 Minfei Huang    2016-05-27  94  					     src->tsc_shift);
3aed64f6d Paolo Bonzini   2016-06-09  95  	return src->system_time + offset;
dce2db0a3 Marcelo Tosatti 2012-11-27  96  }
dce2db0a3 Marcelo Tosatti 2012-11-27  97  

:::::: The code at line 93 was first introduced by commit
:::::: a5a1d1c2914b5316924c7893eb683a5420ebd3be clocksource: Use a plain u64 instead of cycle_t

:::::: TO: Thomas Gleixner <tglx@...utronix.de>
:::::: CC: Thomas Gleixner <tglx@...utronix.de>

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