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

[Dave Anderson]

----- Original Message -----
> 
> If SLAB_RED_ZONE is enabled, slub adds guard zone of sizeof(void *)
> onto head of slab page (red zone padding of left of object) on v4.6 or
> later.
> 
> Without this fix, like following SUPERBLK and [allocate addr] has
> difference.
> 
> crash> mount
>      MOUNT           SUPERBLK     TYPE   DEVNAME   DIRNAME
> ffff88013ae58040 ffff88013ac35698 rootfs rootfs    /
> [...]
> crash> kmem ffff88013ac35698
> CACHE            NAME                 OBJSIZE  ALLOCATED     TOTAL  SLABS  SSIZE
> ffff88013ac05bc0 kmalloc-4096            4096        118       126     18  32k
>   SLAB              MEMORY            NODE  TOTAL  ALLOCATED  FREE
>   ffffea0004eb0c00  ffff88013ac30000     0      7          7     0
>   FREE / [ALLOCATED]
>   [ffff88013ac35690]
> [...]

Hi Ogawa,

When you enter "kmem ffff88013ac35698", I am presuming that it it shows the [ALLOCATED]
object at ffff88013ac35690 as shown above.  If that's true, then in my opinion, it's doing
the right thing.  

I understand that the kmalloc caller receives ffff88013ac35698, but with respect to the
slab subsystem itself, the actual address of the slab object is ffff88013ac35690.  I worry
about the potential consequences of making such a wholesale change to the kmem command.

Dave


> ---
> 
>  defs.h    |    1 +
>  memory.c  |    8 ++++++++
>  symbols.c |    2 ++
>  3 files changed, 11 insertions(+)
> 
> diff -puN memory.c~slub-red_zone-fix memory.c
> --- crash-64/memory.c~slub-red_zone-fix	2017-01-30 10:21:12.123644726 +0900
> +++ crash-64-hirofumi/memory.c	2017-01-30 10:21:12.127644748 +0900
> @@ -723,6 +723,7 @@ vm_init(void)
>  		MEMBER_OFFSET_INIT(kmem_cache_node, "kmem_cache", "node");
>  		MEMBER_OFFSET_INIT(kmem_cache_cpu_slab, "kmem_cache", "cpu_slab");
>  		MEMBER_OFFSET_INIT(kmem_cache_list, "kmem_cache", "list");
> +		MEMBER_OFFSET_INIT(kmem_cache_red_left_pad, "kmem_cache", "red_left_pad");
>  		MEMBER_OFFSET_INIT(kmem_cache_name, "kmem_cache", "name");
>  		MEMBER_OFFSET_INIT(kmem_cache_flags, "kmem_cache", "flags");
>  		MEMBER_OFFSET_INIT(kmem_cache_cpu_freelist, "kmem_cache_cpu", "freelist");
> @@ -18442,6 +18443,13 @@ do_slab_slub(struct meminfo *si, int ver
>  			fprintf(fp, "< SLUB: free list END (%d found) >\n", i);
>  	}
>  
> +	if (VALID_MEMBER(kmem_cache_red_left_pad)) {
> +#define SLAB_RED_ZONE 0x00000400UL
> +		ulong flags = ULONG(si->cache_buf + OFFSET(kmem_cache_flags));
> +		ulong red_left_pad = ULONG(si->cache_buf +
> OFFSET(kmem_cache_red_left_pad));
> +		if (flags & SLAB_RED_ZONE)
> +			vaddr += red_left_pad;
> +	}
>  	for (p = vaddr; p < vaddr + objects * si->size; p += si->size) {
>  		hq_open();
>  		is_free = FALSE;
> diff -puN defs.h~slub-red_zone-fix defs.h
> --- crash-64/defs.h~slub-red_zone-fix	2017-01-30 10:21:12.124644731 +0900
> +++ crash-64-hirofumi/defs.h	2017-02-01 00:11:33.445552457 +0900
> @@ -1696,6 +1696,7 @@ struct offset_table {
>  	long kmem_cache_align;
>  	long kmem_cache_name;
>  	long kmem_cache_list;
> +	long kmem_cache_red_left_pad;
>  	long kmem_cache_node;
>  	long kmem_cache_cpu_slab;
>  	long page_inuse;
> diff -puN symbols.c~slub-red_zone-fix symbols.c
> --- crash-64/symbols.c~slub-red_zone-fix	2017-01-30 10:21:12.124644731 +0900
> +++ crash-64-hirofumi/symbols.c	2017-02-01 00:11:33.446552463 +0900
> @@ -9330,6 +9330,8 @@ dump_offset_table(char *spec, ulong make
>                  OFFSET(kmem_cache_name));
>          fprintf(fp, "               kmem_cache_list: %ld\n",
>                  OFFSET(kmem_cache_list));
> +        fprintf(fp, "       kmem_cache_red_left_pad: %ld\n",
> +                OFFSET(kmem_cache_red_left_pad));
>          fprintf(fp, "               kmem_cache_node: %ld\n",
>                  OFFSET(kmem_cache_node));
>          fprintf(fp, "           kmem_cache_cpu_slab: %ld\n",
> _
> 
> --
> OGAWA Hirofumi <hirofumi at mail.parknet.co.jp>
> 
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