Re: [RFC PATCH 1/5] mm, slub: extend slub_debug syntax for multiple blocks

[Kees Cook]

On Tue, Jun 02, 2020 at 04:15:15PM +0200, Vlastimil Babka wrote:
> The slub_debug kernel boot parameter can either apply a single set of options
> to all caches or a list of caches. There is a use case where debugging is
> applied for all caches and then disabled at runtime for specific caches, for
> performance and memory consumption reasons [1]. As runtime changes are
> dangerous, extend the boot parameter syntax so that multiple blocks of either
> global or slab-specific options can be specified, with blocks delimited by ';'.
> This will also support the use case of [1] without runtime changes.
> 
> For details see the updated Documentation/vm/slub.rst
> 
> [1] https://lore.kernel.org/r/1383cd32-1ddc-4dac-b5f8-9c42282fa81c@xxxxxxxxxxxxxx
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> ---
>  .../admin-guide/kernel-parameters.txt         |   2 +-
>  Documentation/vm/slub.rst                     |  17 ++
>  mm/slub.c                                     | 177 +++++++++++++-----
>  3 files changed, 144 insertions(+), 52 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 6253849afac2..6ea00c8dd635 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4613,7 +4613,7 @@
>  			fragmentation.  Defaults to 1 for systems with
>  			more than 32MB of RAM, 0 otherwise.
>  
> -	slub_debug[=options[,slabs]]	[MM, SLUB]
> +	slub_debug[=options[,slabs][;[options[,slabs]]...]	[MM, SLUB]
>  			Enabling slub_debug allows one to determine the
>  			culprit if slab objects become corrupted. Enabling
>  			slub_debug can create guard zones around objects and
> diff --git a/Documentation/vm/slub.rst b/Documentation/vm/slub.rst
> index 4eee598555c9..f1154f707e06 100644
> --- a/Documentation/vm/slub.rst
> +++ b/Documentation/vm/slub.rst
> @@ -41,6 +41,11 @@ slub_debug=<Debug-Options>,<slab name1>,<slab name2>,...
>  	Enable options only for select slabs (no spaces
>  	after a comma)
>  
> +Multiple blocks of options for all slabs or selected slabs can be given, with
> +blocks of options delimited by ';'. The last of "all slabs" blocks is applied
> +to all slabs except those that match one of the "select slabs" block. Options
> +of the first "select slabs" blocks that matches the slab's name are applied.
> +
>  Possible debug options are::
>  
>  	F		Sanity checks on (enables SLAB_DEBUG_CONSISTENCY_CHECKS
> @@ -83,6 +88,18 @@ in low memory situations or if there's high fragmentation of memory.  To
>  
>  	slub_debug=O
>  
> +You can apply different options to different list of slab names, using blocks
> +of options. This will enable red zoning for dentry and user tracking for
> +kmalloc. All other slabs will not get any debugging enabled::
> +
> +	slub_debug=Z,dentry;U,kmalloc-*
> +
> +You can also enable options (e.g. sanity checks and poisoning) for all caches
> +except some that are deemed too performance critical and don't need to be
> +debugged::

Just for more clarity, how about:

 ... debugged by starting the list with "-" (to mean "all except the
following")::

> +
> +	slub_debug=FZ;-,zs_handle,zspage
> +
>  In case you forgot to enable debugging on the kernel command line: It is
>  possible to enable debugging manually when the kernel is up. Look at the
>  contents of::

Everything else looks great; very nice! :)

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook