Re: [PATCH v3] mm/slub: initialize stack depot in boot process

[Hyeonggon Yoo]

On Tue, Mar 01, 2022 at 10:14:30AM +0100, Vlastimil Babka wrote:
> On 3/1/22 09:51, Hyeonggon Yoo wrote:
> > commit ba10d4b46655 ("mm/slub: use stackdepot to save stack trace in
> > objects") initializes stack depot in cache creation if SLAB_STORE_USER
> > flag is set.
> 
> As pointed out, this is not a stable commit, the series was just posted for
> review and there will be v2. So instead of "this fixes the commit..." I
> suggest writing the patch assuming it's a preparation for the patch
> "mm/slub: use stackdepot"... and I can then make it part of the series.
> So it should instead explain that for slub_debug we will need a way to
> trigger stack_depot_early_init() based on boot options and so this patch
> introduces it...
>

Agreed.

> > This can make kernel crash because a cache can be crashed in various
> > contexts. For example if user sets slub_debug=U, kernel crashes
> > because create_boot_cache() calls stack_depot_init(), which tries to
> > allocate hash table using memblock_alloc() if slab is not available.
> > But memblock is also not available at that time.
> > 
> > This patch solves the problem by initializing stack depot early
> > in boot process if SLAB_STORE_USER debug flag is set globally
> > or the flag is set for at least one cache.
> > 
> > [ elver@xxxxxxxxxx: initialize stack depot depending on slub_debug
> >   parameter instead of allowing stack_depot_init() to be called
> >   during kmem_cache_init() for simplicity. ]
> > 
> > [ vbabka@xxxxxxx: parse slub_debug parameter in setup_slub_debug()
> >   and initialize stack depot in stack_depot_early_init(). ]
> > 
> > [ lkp@xxxxxxxxx: Fix build error. ]
> > 
> > Link: https://lore.kernel.org/all/YhyeaP8lrzKgKm5A@xxxxxxxxxxxxxxxxxxx-northeast-1.compute.internal/
> > Fixes: ba10d4b46655 ("mm/slub: use stackdepot to save stack trace in objects")
> > Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> > ---
> >  include/linux/slab.h       |  1 +
> >  include/linux/stackdepot.h |  3 ++-
> >  mm/slab.c                  |  5 +++++
> >  mm/slob.c                  |  5 +++++
> >  mm/slub.c                  | 19 ++++++++++++++++---
> >  5 files changed, 29 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/slab.h b/include/linux/slab.h
> > index 37bde99b74af..d2b0f8f9e5e6 100644
> > --- a/include/linux/slab.h
> > +++ b/include/linux/slab.h
> > @@ -762,6 +762,7 @@ extern void kvfree_sensitive(const void *addr, size_t len);
> >  
> >  unsigned int kmem_cache_size(struct kmem_cache *s);
> >  void __init kmem_cache_init_late(void);
> > +int __init slab_stack_depot_init(void);
> >  
> >  #if defined(CONFIG_SMP) && defined(CONFIG_SLAB)
> >  int slab_prepare_cpu(unsigned int cpu);
> > diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
> > index 17f992fe6355..a813a2673c48 100644
> > --- a/include/linux/stackdepot.h
> > +++ b/include/linux/stackdepot.h
> > @@ -12,6 +12,7 @@
> >  #define _LINUX_STACKDEPOT_H
> >  
> >  #include <linux/gfp.h>
> > +#include <linux/slab.h>
> >  
> >  typedef u32 depot_stack_handle_t;
> >  
> > @@ -32,7 +33,7 @@ int stack_depot_init(void);
> >  #ifdef CONFIG_STACKDEPOT_ALWAYS_INIT
> >  static inline int stack_depot_early_init(void)	{ return stack_depot_init(); }
> >  #else
> > -static inline int stack_depot_early_init(void)	{ return 0; }
> > +static inline int stack_depot_early_init(void)	{ return slab_stack_depot_init(); }
> >  #endif
> 
> I think the approach should be generic for stackdepot, not tied to a
> function that belongs to slab with 3 different implementations.
> E.g. in stackdepot.h declare a variable e.g. "stack_depot_want_early_init"
> that is checked in stack_depot_early_init() above to call stack_depot_init().

Hmm yeah if we define it in stack depot, that would be nice.
I just didn't want to expose global variable that is specific to slub.

> >  depot_stack_handle_t stack_depot_save(unsigned long *entries,
> > diff --git a/mm/slab.c b/mm/slab.c
> > index ddf5737c63d9..c7f929665fbe 100644
> > --- a/mm/slab.c
> > +++ b/mm/slab.c
> > @@ -1196,6 +1196,11 @@ static void __init set_up_node(struct kmem_cache *cachep, int index)
> >  	}
> >  }
> >  
> > +int __init slab_stack_depot_init(void)
> > +{
> > +	return 0;
> > +}
> > +
> >  /*
> >   * Initialisation.  Called after the page allocator have been initialised and
> >   * before smp_init().
> > diff --git a/mm/slob.c b/mm/slob.c
> > index 60c5842215f1..7597c219f061 100644
> > --- a/mm/slob.c
> > +++ b/mm/slob.c
> > @@ -725,3 +725,8 @@ void __init kmem_cache_init_late(void)
> >  {
> >  	slab_state = FULL;
> >  }
> > +
> > +int __init slab_stack_depot_init(void)
> > +{
> > +	return 0;
> > +}
> > diff --git a/mm/slub.c b/mm/slub.c
> > index a74afe59a403..8f130f917977 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -646,6 +646,16 @@ static slab_flags_t slub_debug;
> >  
> >  static char *slub_debug_string;
> >  static int disable_higher_order_debug;
> > +static bool __initdata init_stack_depot;
> > +
> > +int __init slab_stack_depot_init(void)
> > +{
> > +#ifdef CONFIG_STACKDEPOT
> > +	if (init_stack_depot)
> > +		stack_depot_init();
> > +#endif
> > +	return 0;
> > +}
> 
> 
> 
> >  /*
> >   * slub is about to manipulate internal object metadata.  This memory lies
> > @@ -1531,6 +1541,8 @@ static int __init setup_slub_debug(char *str)
> >  			global_slub_debug_changed = true;
> >  		} else {
> >  			slab_list_specified = true;
> > +			if (flags & SLAB_STORE_USER)
> > +				init_stack_depot = true;
> >  		}
> >  	}
> >  
> > @@ -1546,6 +1558,10 @@ static int __init setup_slub_debug(char *str)
> >  			global_flags = slub_debug;
> >  		slub_debug_string = saved_str;
> >  	}
> > +
> > +	if (global_flags & SLAB_STORE_USER)
> > +		init_stack_depot = true;
> 
> This looks good, it would just set the "stack_depot_want_early_init"
> variable instead. But logically should be part of "mm/slub: use
> stackdepot...", not part of patch that introduces the variable. That so if
> you don't mind I would move it there with credit.
>

Oh I don't mind that.
Then I will expect this to be solved in next series...

I'm looking forward to next version. Thanks!
-- 
Thank you, You are awesome!
Hyeonggon :-)

> >  out:
> >  	slub_debug = global_flags;
> >  	if (slub_debug != 0 || slub_debug_string)
> > @@ -4221,9 +4237,6 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
> >  	s->remote_node_defrag_ratio = 1000;
> >  #endif
> >  
> > -	if (s->flags & SLAB_STORE_USER && IS_ENABLED(CONFIG_STACKDEPOT))
> > -		stack_depot_init();
> > -
> >  	/* Initialize the pre-computed randomized freelist if slab is up */
> >  	if (slab_state >= UP) {
> >  		if (init_cache_random_seq(s))
>