Re: svn commit: r214611 - head/sys/kern

On 1 November 2010 03:42, David Xu <davidxu_at_freebsd.org> wrote:
> Author: davidxu
> Date: Mon Nov  1 00:42:25 2010
> New Revision: 214611
> URL: http://svn.freebsd.org/changeset/base/214611
>
> Log:
>  Use integer for size of cpuset, as it won't be bigger than INT_MAX,
>  This is requested by bge.
>  Also move the sysctl into file kern_cpuset.c, because it should
>  always be there, it is independent of thread scheduler.

Hi.
This breaks for me fetching a cpusetsize value with sysconf(3) interface,
as after this change sysconf(3) consumers expect a long return type, while
sysctl kern.sched.cpusetsize has switched from long to int type in kernel.
That makes for me sizeof(cpusize_t) from 8 to incorrect 34359738376.

In particular, kvm_getpcpu(3) uses sysconf(3) to fetch cpusetsize on
live kernel. That gives me a broken result:
kvm_open: kcpusetsize: 8
pcpu[0] = 0x801072300
kvm_open: kcpusetsize: 34359738376
pcpu[1] = 0xffffffffffffffff
kvm_open: kcpusetsize: 8
pcpu[2] = 0x801072600
kvm_open: kcpusetsize: 34359738376
pcpu[3] = 0xffffffffffffffff

This small test indicates that that's due to int->long type conversion:
        long lvalue;
        size_t len;

        len = sizeof(lvalue);
        if (sysctlbyname("kern.sched.cpusetsize", &lvalue, &len, NULL, 0) < 0)
                err(1, "sysctlbyname");
        printf("sysctl: %ld\n", lvalue);
        printf("sysctl: %d -- explicitly casted to (int)\n", (int)lvalue);
        printf("sysconf: %ld\n", sysconf(_SC_CPUSET_SIZE));
        printf("sysconf: %d -- explicitly casted to (int)\n",
(int)sysconf(_SC_CPUSET_SIZE));

That prints:
sysctl: 34359738376
sysctl: 8 -- explicitly casted to (int)
sysconf: 34359738376
sysconf: 8 -- explicitly casted to (int)

The other way to solve this other than reverting is to "fix" all cpusetsize
consumers in userland. Now sysconf() saves long returned value to int:

Index: lib/libkvm/kvm_pcpu.c
===================================================================
--- lib/libkvm/kvm_pcpu.c       (revision 223073)
+++ lib/libkvm/kvm_pcpu.c       (working copy)
_at__at_ -120,7 +120,7 _at__at_
 void *
 kvm_getpcpu(kvm_t *kd, int cpu)
 {
-       long kcpusetsize;
+       int kcpusetsize;
        ssize_t nbytes;
        uintptr_t readptr;
        char *buf;

So, after applying the above change all is ok:
kvm_open: kcpusetsize: 8
pcpu[0] = 0x801072300
kvm_open: kcpusetsize: 8
pcpu[1] = 0x801072600
kvm_open: kcpusetsize: 8
pcpu[2] = 0x801072900
kvm_open: kcpusetsize: 8
pcpu[3] = 0x801072c00


>
> Modified:
>  head/sys/kern/kern_cpuset.c
>  head/sys/kern/sched_ule.c
>
> Modified: head/sys/kern/kern_cpuset.c
> ==============================================================================
> --- head/sys/kern/kern_cpuset.c Sun Oct 31 23:04:15 2010        (r214610)
> +++ head/sys/kern/kern_cpuset.c Mon Nov  1 00:42:25 2010        (r214611)
> _at__at_ -107,6 +107,10 _at__at_ static struct setlist cpuset_ids;
>  static struct unrhdr *cpuset_unr;
>  static struct cpuset *cpuset_zero;
>
> +/* Return the size of cpuset_t at the kernel level */
> +SYSCTL_INT(_kern_sched, OID_AUTO, cpusetsize, CTLFLAG_RD,
> +       0, sizeof(cpuset_t), "sizeof(cpuset_t)");
> +
>  cpuset_t *cpuset_root;
>
>  /*
>
> Modified: head/sys/kern/sched_ule.c
> ==============================================================================
> --- head/sys/kern/sched_ule.c   Sun Oct 31 23:04:15 2010        (r214610)
> +++ head/sys/kern/sched_ule.c   Mon Nov  1 00:42:25 2010        (r214611)
> _at__at_ -2713,7 +2713,6 _at__at_ sysctl_kern_sched_topology_spec(SYSCTL_H
>        return (err);
>  }
>
> -static size_t _kern_cpuset_size = sizeof(cpuset_t);
>  #endif
>
>  SYSCTL_NODE(_kern, OID_AUTO, sched, CTLFLAG_RW, 0, "Scheduler");
> _at__at_ -2751,14 +2750,6 _at__at_ SYSCTL_PROC(_kern_sched, OID_AUTO, topol
>     CTLFLAG_RD, NULL, 0, sysctl_kern_sched_topology_spec, "A",
>     "XML dump of detected CPU topology");
>
> -/*
> - * Return the size of cpuset_t at the kernel level
> - *
> - * XXX (gcooper): replace ULONG with SIZE once CTLTYPE_SIZE is implemented.
> - */
> -SYSCTL_ULONG(_kern_sched, OID_AUTO, cpusetsize, CTLFLAG_RD,
> -    &_kern_cpuset_size, 0, "Kernel-level cpuset_t struct size");
> -
>  #endif
>
>  /* ps compat.  All cpu percentages from ULE are weighted. */
>

-- 
wbr,
pluknet