[Crash-utility] [PATCH] Fix for "kmem <addr>" for kernels configured with CONFIG_SLUB and SLAB_RED_ZONE.

[Dave Anderson]

----- Original Message -----

> 
> OK, I understand.  Let me work on a new "set redzone on/off" environment
> variable that can be toggled on-and-off during runtime.
> 
> But I believe I see a problem in do_slab_slub().  When it is checking for free
> objects to display as FREE / [ALLOCATED], it will never find it in 4.6+ kernels
> with a red_left_pad.  Note below, when it checks whether (p == q), the "q" address
> is the "shifted" address seen by the kmalloc() caller, and will never match the
> base object address "p", so "is_free" never gets set:
> 
>         for (p = vaddr; p < vaddr + objects * si->size; p += si->size) {
>                 hq_open();
>                 is_free = FALSE;
>                 /* Search an object on both of freelist and cpu_freelist */
>                 ulong lists[] = { freelist, cpu_freelist, };
>                 for (i = 0; i < sizeof(lists) / sizeof(lists[0]); i++) {
>                         for (is_free = 0, q = lists[i]; q;
>                              q = get_freepointer(si, (void *)q)) {
> 
>                                 if (q == BADADDR) {
>                                         hq_close();
>                                         return FALSE;
>                                 }
>                                 if (q & PAGE_MAPPING_ANON)
>                                         break;
> === never can match ===>        if (p == q) {
>                                         is_free = TRUE;
>                                         goto found_object;
>                                 }
>                                 if (!hq_enter(q)) {
>                                         hq_close();
>                                         error(INFO, "%s: slab: %lx duplicate
>                                         freelist object: %lx\n",
>                                               si->curname, si->slab, q);
>                                         return FALSE;
>                                 }
>                         }
>                 }
>         found_object:
> ...
> 
> Do you agree?

Ah -- I see that your first patch modified vaddr *before* the code segment
above.  That would work in the case where the adjusted red-zone address
is used.  But in order to handle both cases, the patch will need to be
adjusted for when the base address is used unmodified. 

Dave