Re: [PATCH v2 3/6] mm/slub: use stackdepot to save stack trace in objects

[Hyeonggon Yoo]

On Wed, Mar 02, 2022 at 06:31:19PM +0100, Vlastimil Babka wrote:
> From: Oliver Glitta <glittao@xxxxxxxxx>
> 
> Many stack traces are similar so there are many similar arrays.
> Stackdepot saves each unique stack only once.
> 
> Replace field addrs in struct track with depot_stack_handle_t handle.  Use
> stackdepot to save stack trace.
> 
> The benefits are smaller memory overhead and possibility to aggregate
> per-cache statistics in the following patch using the stackdepot handle
> instead of matching stacks manually.
> 
> [ vbabka@xxxxxxx: rebase to 5.17-rc1 and adjust accordingly ]
> 
> This was initially merged as commit 788691464c29 and reverted by commit
> ae14c63a9f20 due to several issues, that should now be fixed.
> The problem of unconditional memory overhead by stackdepot has been
> addressed by commit 2dba5eb1c73b ("lib/stackdepot: allow optional init
> and stack_table allocation by kvmalloc()"), so the dependency on
> stackdepot will result in extra memory usage only when a slab cache
> tracking is actually enabled, and not for all CONFIG_SLUB_DEBUG builds.
> The build failures on some architectures were also addressed, and the
> reported issue with xfs/433 test did not reproduce on 5.17-rc1 with this
> patch.
> 
> Signed-off-by: Oliver Glitta <glittao@xxxxxxxxx>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> ---
>  init/Kconfig     |  1 +
>  mm/slab_common.c |  5 ++++
>  mm/slub.c        | 71 +++++++++++++++++++++++++++---------------------
>  3 files changed, 46 insertions(+), 31 deletions(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index e9119bf54b1f..b21dd3a4a106 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1871,6 +1871,7 @@ config SLUB_DEBUG
>  	default y
>  	bool "Enable SLUB debugging support" if EXPERT
>  	depends on SLUB && SYSFS
> +	select STACKDEPOT if STACKTRACE_SUPPORT
>  	help
>  	  SLUB has extensive debug support features. Disabling these can
>  	  result in significant savings in code size. This also disables
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 23f2ab0713b7..e51d50d03000 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -24,6 +24,7 @@
>  #include <asm/tlbflush.h>
>  #include <asm/page.h>
>  #include <linux/memcontrol.h>
> +#include <linux/stackdepot.h>
>  
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/kmem.h>
> @@ -314,9 +315,13 @@ kmem_cache_create_usercopy(const char *name,
>  	 * If no slub_debug was enabled globally, the static key is not yet
>  	 * enabled by setup_slub_debug(). Enable it if the cache is being
>  	 * created with any of the debugging flags passed explicitly.
> +	 * It's also possible that this is the first cache created with
> +	 * SLAB_STORE_USER and we should init stack_depot for it.
>  	 */
>  	if (flags & SLAB_DEBUG_FLAGS)
>  		static_branch_enable(&slub_debug_enabled);
> +	if (flags & SLAB_STORE_USER && IS_ENABLED(CONFIG_STACKDEPOT))
> +		stack_depot_init();
>  #endif

Is this comment and code still valid in v3?

>  	mutex_lock(&slab_mutex);
> diff --git a/mm/slub.c b/mm/slub.c
> index 1fc451f4fe62..42cb79af70a0 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -26,6 +26,7 @@
>  #include <linux/cpuset.h>
>  #include <linux/mempolicy.h>
>  #include <linux/ctype.h>
> +#include <linux/stackdepot.h>
>  #include <linux/debugobjects.h>
>  #include <linux/kallsyms.h>
>  #include <linux/kfence.h>
> @@ -264,8 +265,8 @@ static inline bool kmem_cache_has_cpu_partial(struct kmem_cache *s)
>  #define TRACK_ADDRS_COUNT 16
>  struct track {
>  	unsigned long addr;	/* Called from address */
> -#ifdef CONFIG_STACKTRACE
> -	unsigned long addrs[TRACK_ADDRS_COUNT];	/* Called from address */
> +#ifdef CONFIG_STACKDEPOT
> +	depot_stack_handle_t handle;
>  #endif
>  	int cpu;		/* Was running on cpu */
>  	int pid;		/* Pid context */
> @@ -724,22 +725,19 @@ static struct track *get_track(struct kmem_cache *s, void *object,
>  	return kasan_reset_tag(p + alloc);
>  }
>  
> -static void set_track(struct kmem_cache *s, void *object,
> +static void noinline set_track(struct kmem_cache *s, void *object,
>  			enum track_item alloc, unsigned long addr)
>  {

noinline for debugging purpose?
I think it's okay. just a question.

>  	struct track *p = get_track(s, object, alloc);
>  
> -#ifdef CONFIG_STACKTRACE
> +#ifdef CONFIG_STACKDEPOT
> +	unsigned long entries[TRACK_ADDRS_COUNT];
>  	unsigned int nr_entries;
>  
> -	metadata_access_enable();
> -	nr_entries = stack_trace_save(kasan_reset_tag(p->addrs),
> -				      TRACK_ADDRS_COUNT, 3);
> -	metadata_access_disable();
> -
> -	if (nr_entries < TRACK_ADDRS_COUNT)
> -		p->addrs[nr_entries] = 0;
> +	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 3);
> +	p->handle = stack_depot_save(entries, nr_entries, GFP_NOWAIT);
>  #endif
> +
>  	p->addr = addr;
>  	p->cpu = smp_processor_id();
>  	p->pid = current->pid;
> @@ -759,20 +757,19 @@ static void init_tracking(struct kmem_cache *s, void *object)
>  
>  static void print_track(const char *s, struct track *t, unsigned long pr_time)
>  {
> +	depot_stack_handle_t handle __maybe_unused;
> +
>  	if (!t->addr)
>  		return;
>  
>  	pr_err("%s in %pS age=%lu cpu=%u pid=%d\n",
>  	       s, (void *)t->addr, pr_time - t->when, t->cpu, t->pid);
> -#ifdef CONFIG_STACKTRACE
> -	{
> -		int i;
> -		for (i = 0; i < TRACK_ADDRS_COUNT; i++)
> -			if (t->addrs[i])
> -				pr_err("\t%pS\n", (void *)t->addrs[i]);
> -			else
> -				break;
> -	}
> +#ifdef CONFIG_STACKDEPOT
> +	handle = READ_ONCE(t->handle);
> +	if (handle)
> +		stack_depot_print(handle);
> +	else
> +		pr_err("object allocation/free stack trace missing\n");
>  #endif
>  }
>  
> @@ -1532,6 +1529,8 @@ static int __init setup_slub_debug(char *str)
>  			global_slub_debug_changed = true;
>  		} else {
>  			slab_list_specified = true;
> +			if (flags & SLAB_STORE_USER)
> +				stack_depot_want_early_init = true;

This is updated to stack_depot_want_early_init() in v3.

>  		}
>  	}
>  
> @@ -1549,6 +1548,8 @@ static int __init setup_slub_debug(char *str)
>  	}
>  out:
>  	slub_debug = global_flags;
> +	if (slub_debug & SLAB_STORE_USER)
> +		stack_depot_want_early_init = true;

This too.

>  	if (slub_debug != 0 || slub_debug_string)
>  		static_branch_enable(&slub_debug_enabled);
>  	else
> @@ -4352,18 +4353,26 @@ void kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
>  	objp = fixup_red_left(s, objp);
>  	trackp = get_track(s, objp, TRACK_ALLOC);
>  	kpp->kp_ret = (void *)trackp->addr;
> -#ifdef CONFIG_STACKTRACE
> -	for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
> -		kpp->kp_stack[i] = (void *)trackp->addrs[i];
> -		if (!kpp->kp_stack[i])
> -			break;
> -	}
> +#ifdef CONFIG_STACKDEPOT
> +	{
> +		depot_stack_handle_t handle;
> +		unsigned long *entries;
> +		unsigned int nr_entries;
> +
> +		handle = READ_ONCE(trackp->handle);
> +		if (handle) {
> +			nr_entries = stack_depot_fetch(handle, &entries);
> +			for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
> +				kpp->kp_stack[i] = (void *)entries[i];
> +		}
>  
> -	trackp = get_track(s, objp, TRACK_FREE);
> -	for (i = 0; i < KS_ADDRS_COUNT && i < TRACK_ADDRS_COUNT; i++) {
> -		kpp->kp_free_stack[i] = (void *)trackp->addrs[i];
> -		if (!kpp->kp_free_stack[i])
> -			break;
> +		trackp = get_track(s, objp, TRACK_FREE);
> +		handle = READ_ONCE(trackp->handle);
> +		if (handle) {
> +			nr_entries = stack_depot_fetch(handle, &entries);
> +			for (i = 0; i < KS_ADDRS_COUNT && i < nr_entries; i++)
> +				kpp->kp_free_stack[i] = (void *)entries[i];
> +		}
>  	}
>  #endif
>  #endif
> -- 
> 2.35.1

Otherwise looks good.
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

kmem_dump_obj() and slab error report functionality works fine.
Tested-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

-- 
Thank you, You are awesome!
Hyeonggon :-)