[Crash-utility] [PATCH] Add support for SLAB OBJFREELIST_SLAB.

[Dave Anderson]

----- Original Message -----
> That was quick.
> 
> Thanks Dave!

Yeah, I was only able to test it for backwards-compatibility on a handful
of sample pre-4.6 SLAB kernels because RHEL/Fedora uses SLUB, so I'm totally
trusting your preceding reputation...

Thanks again, 

Dave

> 
> On Fri, Dec 2, 2016 at 10:59 AM, Dave Anderson <anderson at redhat.com> wrote:
> 
> >
> >
> > ----- Original Message -----
> > > In this mode, the freelist can be an object and if the slab is full,
> > > there is no freelist. On the next free, an object is recycled to be used
> > > as the freelist but not clean-up. This change will go through only
> > > known freed objects to prevent errors of wrong/corrupt freelist entries.
> > >
> > > Related to the linux kernel commit: b03a017bebc403d40aa53a092e79b3
> > 020786537d.
> >
> > Thanks Thomas -- the patch queued for crash-7.1.8:
> >
> >   https://github.com/crash-utility/crash/commit/
> > 59fbaf3e4b030b150f750f5b0ac7dfc3eafaa78f
> >
> > Dave
> >
> >
> > > ---
> > >  memory.c | 30 ++++++++++++++++++++++++------
> > >  1 file changed, 24 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/memory.c b/memory.c
> > > index 4eac413..774d090 100644
> > > --- a/memory.c
> > > +++ b/memory.c
> > > @@ -9880,6 +9880,7 @@ ignore_cache(struct meminfo *si, char *name)
> > >  #define SLAB_MAGIC_DESTROYED    0xB2F23C5AUL    /* slab has been
> > destroyed
> > >  */
> > >
> > >  #define SLAB_CFLGS_BUFCTL       0x020000UL      /* bufctls in own cache
> > */
> > > +#define SLAB_CFLGS_OBJFREELIST  0x40000000UL    /* Freelist as an
> > object */
> > >
> > >  #define KMEM_SLAB_ADDR          (1)
> > >  #define KMEM_BUFCTL_ADDR        (2)
> > > @@ -12439,11 +12440,13 @@ gather_slab_free_list_percpu(struct meminfo
> > *si)
> > >  static void
> > >  gather_slab_free_list_slab_overload_page(struct meminfo *si)
> > >  {
> > > -     int i, active;
> > > +     int i, active, start_offset;
> > >       ulong obj, objnr, cnt, freelist;
> > >       unsigned char *ucharptr;
> > >       unsigned short *ushortptr;
> > >       unsigned int *uintptr;
> > > +     unsigned int cache_flags, overload_active;
> > > +     ulong slab_overload_page;
> > >
> > >       if (CRASHDEBUG(1))
> > >               fprintf(fp, "slab page: %lx active: %ld si->c_num: %ld\n",
> > > @@ -12452,12 +12455,19 @@ gather_slab_free_list_slab_
> > overload_page(struct
> > > meminfo *si)
> > >       if (si->s_inuse == si->c_num )
> > >               return;
> > >
> > > -     readmem(si->slab - OFFSET(page_lru) + OFFSET(page_freelist),
> > > +     slab_overload_page = si->slab - OFFSET(page_lru);
> > > +     readmem(slab_overload_page + OFFSET(page_freelist),
> > >               KVADDR, &freelist, sizeof(void *), "page freelist",
> > >               FAULT_ON_ERROR);
> > >          readmem(freelist, KVADDR, si->freelist,
> > >               si->freelist_index_size * si->c_num,
> > >                  "freelist array", FAULT_ON_ERROR);
> > > +     readmem(si->cache+OFFSET(kmem_cache_s_flags),
> > > +             KVADDR, &cache_flags, sizeof(uint),
> > > +             "kmem_cache_s flags", FAULT_ON_ERROR);
> > > +        readmem(slab_overload_page + OFFSET(page_active),
> > > +                KVADDR, &overload_active, sizeof(uint),
> > > +                "active", FAULT_ON_ERROR);
> > >
> > >       BNEG(si->addrlist, sizeof(ulong) * (si->c_num+1));
> > >       cnt = objnr = 0;
> > > @@ -12466,14 +12476,22 @@ gather_slab_free_list_slab_
> > overload_page(struct
> > > meminfo *si)
> > >       uintptr = NULL;
> > >       active = si->s_inuse;
> > >
> > > +     /*
> > > +      * On an OBJFREELIST slab, the object might have been recycled
> > > +      * and everything before the active count can be random data.
> > > +      */
> > > +     start_offset = 0;
> > > +     if (cache_flags & SLAB_CFLGS_OBJFREELIST)
> > > +             start_offset = overload_active;
> > > +
> > >       switch (si->freelist_index_size)
> > >       {
> > > -     case 1: ucharptr = (unsigned char *)si->freelist; break;
> > > -     case 2: ushortptr = (unsigned short *)si->freelist; break;
> > > -     case 4: uintptr = (unsigned int *)si->freelist; break;
> > > +     case 1: ucharptr = (unsigned char *)si->freelist + start_offset;
> > break;
> > > +     case 2: ushortptr = (unsigned short *)si->freelist + start_offset;
> > break;
> > > +     case 4: uintptr = (unsigned int *)si->freelist + start_offset;
> > break;
> > >       }
> > >
> > > -     for (i = 0; i < si->c_num; i++) {
> > > +     for (i = start_offset; i < si->c_num; i++) {
> > >               switch (si->freelist_index_size)
> > >               {
> > >               case 1: objnr = (ulong)*ucharptr++; break;
> > > --
> > > 2.8.0.rc3.226.g39d4020
> > >
> > > --
> > > Crash-utility mailing list
> > > Crash-utility at redhat.com
> > > https://www.redhat.com/mailman/listinfo/crash-utility
> > >
> >
> 
> 
> 
> --
> Thomas
>