Re: svn commit: r322345 - stable/11/lib/libc/x86/sys

[Andre Albsmeier]

On Sun, 13-Aug-2017 at 16:37:36 +0300, Konstantin Belousov wrote:
> On Sun, Aug 13, 2017 at 03:13:11PM +0200, Andre Albsmeier wrote:
> > On Thu, 10-Aug-2017 at 09:00:15 +, Konstantin Belousov wrote:
> > > Author: kib
> > > Date: Thu Aug 10 09:00:15 2017
> > > New Revision: 322345
> > > URL: https://svnweb.freebsd.org/changeset/base/322345
> > > 
> > > Log:
> > >   MFC r321608:
> > >   Use MFENCE to serialize RDTSC on non-Intel CPUs.
> > 
> > This broke libc on my
> > 
> > FreeBSD clang version 4.0.0 (tags/RELEASE_400/final 297347) (based on LLVM 
> > 4.0.0)
> > VT(vga): text 80x25
> > CPU: AMD-K6tm w/ multimedia extensions (199.44-MHz 586-class CPU)
> >   Origin="AuthenticAMD"  Id=0x562  Family=0x5  Model=0x6  Stepping=2
> >   Features=0x8001bf
> >   AMD Features=0x400<>
> > 
> > On system start, it actually makes various programmes hang until
> > Ctrl-C is pressed. Reboot is not possible (endlessly hanging with
> > 'zillions of defunct processes).
> > 
> > Going back to r322042 fixes it...
> 
> Indeed code is broken on i386 machines which have CPUID but no SSE.

Wonder how many of these still exist...

> Try this.

I just compiled and installed libc.so.7 with this patch on the machine
in question and the test I used for hunting down the reason (ls -l /lib) 
was OK. I then rebooted the whole box and it looked good as well.

I did not compile stuff which links libc statically and hung before (devd)
but I am pretty sure this will be OK as well...

Thanks,

-Andre

> 
> diff --git a/lib/libc/x86/sys/__vdso_gettc.c b/lib/libc/x86/sys/__vdso_gettc.c
> index 4ada5e7eac1..ef2ca69edf7 100644
> --- a/lib/libc/x86/sys/__vdso_gettc.c
> +++ b/lib/libc/x86/sys/__vdso_gettc.c
> @@ -101,6 +101,7 @@ init_fence(void)
>  #if defined(__i386__)
>   u_int cpuid_supported, p[4];
>  
> + lfence_works = LMB_NONE;
>   __asm __volatile(
>   "   pushfl\n"
>   "   popl%%eax\n"
> @@ -121,8 +122,7 @@ init_fence(void)
>   cpuidp(0x1, p);
>   if ((p[3] & CPUID_SSE2) != 0)
>   lfence_works = select_lmb();
> - } else
> - lfence_works = LMB_NONE;
> + }
>  #elif defined(__amd64__)
>   lfence_works = select_lmb();
>  #else

-- 
My other computer is your windows box.
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Re: svn commit: r322345 - stable/11/lib/libc/x86/sys

[Konstantin Belousov]

On Sun, Aug 13, 2017 at 03:13:11PM +0200, Andre Albsmeier wrote:
> On Thu, 10-Aug-2017 at 09:00:15 +, Konstantin Belousov wrote:
> > Author: kib
> > Date: Thu Aug 10 09:00:15 2017
> > New Revision: 322345
> > URL: https://svnweb.freebsd.org/changeset/base/322345
> > 
> > Log:
> >   MFC r321608:
> >   Use MFENCE to serialize RDTSC on non-Intel CPUs.
> 
> This broke libc on my
> 
> FreeBSD clang version 4.0.0 (tags/RELEASE_400/final 297347) (based on LLVM 
> 4.0.0)
> VT(vga): text 80x25
> CPU: AMD-K6tm w/ multimedia extensions (199.44-MHz 586-class CPU)
>   Origin="AuthenticAMD"  Id=0x562  Family=0x5  Model=0x6  Stepping=2
>   Features=0x8001bf
>   AMD Features=0x400<>
> 
> On system start, it actually makes various programmes hang until
> Ctrl-C is pressed. Reboot is not possible (endlessly hanging with
> 'zillions of defunct processes).
> 
> Going back to r322042 fixes it...

Indeed code is broken on i386 machines which have CPUID but no SSE.
Try this.

diff --git a/lib/libc/x86/sys/__vdso_gettc.c b/lib/libc/x86/sys/__vdso_gettc.c
index 4ada5e7eac1..ef2ca69edf7 100644
--- a/lib/libc/x86/sys/__vdso_gettc.c
+++ b/lib/libc/x86/sys/__vdso_gettc.c
@@ -101,6 +101,7 @@ init_fence(void)
 #if defined(__i386__)
u_int cpuid_supported, p[4];
 
+   lfence_works = LMB_NONE;
__asm __volatile(
"   pushfl\n"
"   popl%%eax\n"
@@ -121,8 +122,7 @@ init_fence(void)
cpuidp(0x1, p);
if ((p[3] & CPUID_SSE2) != 0)
lfence_works = select_lmb();
-   } else
-   lfence_works = LMB_NONE;
+   }
 #elif defined(__amd64__)
lfence_works = select_lmb();
 #else
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Re: svn commit: r322345 - stable/11/lib/libc/x86/sys

[Andre Albsmeier]

On Thu, 10-Aug-2017 at 09:00:15 +, Konstantin Belousov wrote:
> Author: kib
> Date: Thu Aug 10 09:00:15 2017
> New Revision: 322345
> URL: https://svnweb.freebsd.org/changeset/base/322345
> 
> Log:
>   MFC r321608:
>   Use MFENCE to serialize RDTSC on non-Intel CPUs.

This broke libc on my

FreeBSD clang version 4.0.0 (tags/RELEASE_400/final 297347) (based on LLVM 
4.0.0)
VT(vga): text 80x25
CPU: AMD-K6tm w/ multimedia extensions (199.44-MHz 586-class CPU)
  Origin="AuthenticAMD"  Id=0x562  Family=0x5  Model=0x6  Stepping=2
  Features=0x8001bf
  AMD Features=0x400<>

On system start, it actually makes various programmes hang until
Ctrl-C is pressed. Reboot is not possible (endlessly hanging with
'zillions of defunct processes).

Going back to r322042 fixes it...

-Andre

> 
> Modified:
>   stable/11/lib/libc/x86/sys/__vdso_gettc.c
> Directory Properties:
>   stable/11/   (props changed)
> 
> Modified: stable/11/lib/libc/x86/sys/__vdso_gettc.c
> ==
> --- stable/11/lib/libc/x86/sys/__vdso_gettc.c Thu Aug 10 06:59:43 2017
> (r322344)
> +++ stable/11/lib/libc/x86/sys/__vdso_gettc.c Thu Aug 10 09:00:15 2017
> (r322345)
> @@ -52,57 +52,108 @@ __FBSDID("$FreeBSD$");
>  #endif
>  #include "libc_private.h"
>  
> +static enum LMB {
> + LMB_UNKNOWN,
> + LMB_NONE,
> + LMB_MFENCE,
> + LMB_LFENCE
> +} lfence_works = LMB_UNKNOWN;
> +
>  static void
> -lfence_mb(void)
> +cpuidp(u_int leaf, u_int p[4])
>  {
> +
> + __asm __volatile(
>  #if defined(__i386__)
> - static int lfence_works = -1;
> + "   pushl   %%ebx\n"
> +#endif
> + "   cpuid\n"
> +#if defined(__i386__)
> + "   movl%%ebx,%1\n"
> + "   popl%%ebx"
> +#endif
> + : "=a" (p[0]),
> +#if defined(__i386__)
> + "=r" (p[1]),
> +#elif defined(__amd64__)
> + "=b" (p[1]),
> +#else
> +#error "Arch"
> +#endif
> + "=c" (p[2]), "=d" (p[3])
> + :  "0" (leaf));
> +}
> +
> +static enum LMB
> +select_lmb(void)
> +{
> + u_int p[4];
> + static const char intel_id[] = "GenuntelineI";
> +
> + cpuidp(0, p);
> + return (memcmp(p + 1, intel_id, sizeof(intel_id) - 1) == 0 ?
> + LMB_LFENCE : LMB_MFENCE);
> +}
> +
> +static void
> +init_fence(void)
> +{
> +#if defined(__i386__)
>   u_int cpuid_supported, p[4];
>  
> - if (lfence_works == -1) {
> - __asm __volatile(
> - "   pushfl\n"
> - "   popl%%eax\n"
> - "   movl%%eax,%%ecx\n"
> - "   xorl$0x20,%%eax\n"
> - "   pushl   %%eax\n"
> - "   popfl\n"
> - "   pushfl\n"
> - "   popl%%eax\n"
> - "   xorl%%eax,%%ecx\n"
> - "   je  1f\n"
> - "   movl$1,%0\n"
> - "   jmp 2f\n"
> - "1: movl$0,%0\n"
> - "2:\n"
> - : "=r" (cpuid_supported) : : "eax", "ecx", "cc");
> - if (cpuid_supported) {
> - __asm __volatile(
> - "   pushl   %%ebx\n"
> - "   cpuid\n"
> - "   movl%%ebx,%1\n"
> - "   popl%%ebx\n"
> - : "=a" (p[0]), "=r" (p[1]), "=c" (p[2]), "=d" (p[3])
> - :  "0" (0x1));
> - lfence_works = (p[3] & CPUID_SSE2) != 0;
> - } else
> - lfence_works = 0;
> - }
> - if (lfence_works == 1)
> - lfence();
> + __asm __volatile(
> + "   pushfl\n"
> + "   popl%%eax\n"
> + "   movl%%eax,%%ecx\n"
> + "   xorl$0x20,%%eax\n"
> + "   pushl   %%eax\n"
> + "   popfl\n"
> + "   pushfl\n"
> + "   popl%%eax\n"
> + "   xorl%%eax,%%ecx\n"
> + "   je  1f\n"
> + "   movl$1,%0\n"
> + "   jmp 2f\n"
> + "1: movl$0,%0\n"
> + "2:\n"
> + : "=r" (cpuid_supported) : : "eax", "ecx", "cc");
> + if (cpuid_supported) {
> + cpuidp(0x1, p);
> + if ((p[3] & CPUID_SSE2) != 0)
> + lfence_works = select_lmb();
> + } else
> + lfence_works = LMB_NONE;
>  #elif defined(__amd64__)
> - lfence();
> + lfence_works = select_lmb();
>  #else
> -#error "arch"
> +#error "Arch"
>  #endif
>  }
>  
> +static void
> +rdtsc_mb(void)
> +{
> +
> +again:
> + if (__predict_true(lfence_works == LMB_LFENCE)) {
> + lfence();
> + return;
> + } else if (lfence_works == LMB_MFENCE) {
> + mfence();
> + return;
> + } else if (lfence_works == LMB_NONE) {
> + return;
> + }
> + init_fence();
> + goto