Re: [PATCH] garbage values in file /proc/net/sockstat

[Eric Dumazet <dada1@cosmosbay.com>]

Andi Kleen a écrit :
> On Monday 23 January 2006 12:21, pravin shelar wrote:
> > 	In 2.6.16-rc1-mm1, (for x86_64 arch) cpu_possible_map is not same 
> > as NR_CPUS (prefill_possible_map()). Therefore per cpu areas are allocated 
> > for cpu_possible cpus only (setup_per_cpu_areas()). This causes sockstat 
> > to return garbage value on x84_64 arch.
> >
> > So these per_cpu accesses are geting relocated (RELOC_HIDE) using
> > boot_cpu_pda[]->data_offset which is not initialized.
> >
> > There are other instances of same bug where per_cpu() macro is used
> > without cpu_possible() check. e.g. net/core/utils.c :: 
> > net_random_reseed(), net/core/dev.c :: net_dev_init(), etc.
> >
> > This patch fixes these bugs.
>
> Thanks. Patches Look good.  Dave, can you push them for 2.6.16 still please?

Shouldnt we force a page fault for not possible cpus in cpu_data
to catch all access to per_cpu(some_object, some_not_possible_cpu) ?

We can use a red zone big enough to hold the whole per_cpu data.

Something like :

file include/asm-x86_64/pgtable.h

#define CPUDATA_RED_ZONE 0xffff808000000000UL  /* start of percpu catcher */

file arch/x86_64/kernel/setup64.c

setup_per_cpu_areas(void)
{
...
    for (i = 0 ; i < NR_CPUS ; i++) {
        if (!cpu_possible(cpu))
            cpu_pda(i)->data_offset = CPUDATA_RED_ZONE - __per_cpu_start ;
    }
}

Eric

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