Re: [PATCH] Fix kernel BUGs when enable SLOB allocator

[Nick Piggin <nickpiggin@yahoo.com.au>]

Aubrey wrote:
> Hi all,
>
> When enable the SLOB allocator on a nommu system(uClinux), the
> following bug occurs when remove a large file.
> =========================================================
> root:~> cp /bin/busybox /busy
> root:~> ls -l /bin/busybox /busy
> -rwxr-xr-x    1 0        0          423904 /bin/busybox
> -rwxr-xr-x    1 0        0          423904 /busy
> root:~> md5sum /bin/busybox
> 7db253a2259ab71bc854c9e5dac544d6  /bin/busybox
> root:~> md5sum /busy
> 7db253a2259ab71bc854c9e5dac544d6  /busy
> root:~> rm /busy
> kernel BUG at mm/nommu.c:124!
> Kernel panic - not syncing: BUG!
> =========================================================
>
> The root cause is the slob allocator get the pages but does not set
> the PageSlab bit.
> So when kobjsize is called, the bug occurs.
>
> My patch found a simple way to fix the issue. When SLOB is enabled, we
> don't need to set the PageSlab bit, and don't need to check the
> PageSlab bit(PageSlab(page)) in the kobjsize routine call.
>
> Signed-off-by: Aubrey Li <aubrey.adi@gmail.com>
>
> ------
> diff --git a/mm/nommu.c b/mm/nommu.c
> index 029fada..8a54391 100644
> --- a/mm/nommu.c
> +++ b/mm/nommu.c
> @@ -18,7 +18,9 @@ #include <linux/swap.h>
> #include <linux/file.h>
> #include <linux/highmem.h>
> #include <linux/pagemap.h>
> -#include <linux/slab.h>
> +#ifdef CONFIG_SLAB
> +# include <linux/slab.h>
> +#endif
> #include <linux/vmalloc.h>
> #include <linux/ptrace.h>
> #include <linux/blkdev.h>
> @@ -112,7 +114,9 @@ unsigned int kobjsize(const void *objp)
>        if (!objp || !((page = virt_to_page(objp))))
>                return 0;
>
> +#ifdef CONFIG_SLAB
>        if (PageSlab(page))
> +#endif
>                return ksize(objp);

Then what if objp isn't a slob object?

I think the better fix would be to make slob set PageSlab.

--
SUSE Labs, Novell Inc.
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