[Crash-utility] Crash kmem error

[Dave Anderson]

----- Original Message -----
> Hi,
> 
> When I used crash based off of a mainline kernel to run kmem, it
> failed. For your information, the detailed description of the problem
> is as follows.
> 
> Version-Release number of selected component:
> # uname -a
> Linux hp-rx8640-02.rhts.eng.bos.redhat.com 2.6.39-rc6+ #2 SMP Mon May
> 9 23:05:14 EDT 2011 ia64 ia64 ia64 GNU/Linux
> 
> Steps to Reproduce:
> 1、update the old kernel to the mainline kernel 2.6.39-rc6+
> 2、install crash
> 3、# crash <where the mainline kernel tree is>/vmlinux
> 4、crash> kmem -s
> CACHE NAME OBJSIZE ALLOCATED TOTAL SLABS SSIZE
> 
> kmem: invalid structure member offset: slab_list
> FILE: memory.c LINE: 9588 FUNCTION: verify_slab_v2()
> 
> [/usr/bin/crash] error trace: 40000000000db7c0 => 40000000000ca450 =>
> 40000000000c8ea0 => 40000000001c74a0
> 
> 40000000001c74a0: OFFSET_verify+224
> 40000000000c8ea0: verify_slab_v2+448
> 40000000000ca450: do_slab_chain_percpu_v2_nodes+4208
> 40000000000db7c0: dump_kmem_cache_percpu_v2+3536
> 
> kmem: invalid structure member offset: slab_list
> FILE: memory.c LINE: 9588 FUNCTION: verify_slab_v2()
> 
> 
> Best Regards,
> Qiannan Cui

Yes, I remember seeing the LKML post changing the slab structure
from this:

struct slab {
        struct list_head list;
        unsigned long colouroff;
        void *s_mem;            /* including colour offset */
        unsigned int inuse;     /* num of objs active in slab */
        kmem_bufctl_t free;
        unsigned short nodeid;
};

to this:
 
struct slab {
        union {
                struct {
                        struct list_head list;
                        unsigned long colouroff;
                        void *s_mem;            /* including colour offset */
                        unsigned int inuse;     /* num of objs active in slab */
                        kmem_bufctl_t free;
                        unsigned short nodeid;
                };
                struct slab_rcu __slab_cover_slab_rcu;
        };
};

I had hoped that since the pre-existing fields had been moved
into an anonymous union that the member offsets would be
returned by gdb the same way.  Apparently not:

(gdb) ptype struct slab
type = struct slab {
    union {
        struct {...};
        struct slab_rcu __slab_cover_slab_rcu;
    };
}
(gdb)

But the offsets can be determined in another manner.

Thanks,
  Dave