Date:   Tue, 15 Nov 2022 00:56:14 +0900
From:   Masami Hiramatsu (Google) <mhiramat@...nel.org>
To:     wuqiang <wuqiang.matt@...edance.com>
Cc:     davem@...emloft.net, anil.s.keshavamurthy@...el.com,
        naveen.n.rao@...ux.ibm.com, rostedt@...dmis.org,
        peterz@...radead.org, akpm@...ux-foundation.org,
        sander@...nheule.net, ebiggers@...gle.com,
        dan.j.williams@...el.com, jpoimboe@...nel.org,
        linux-kernel@...r.kernel.org, lkp@...el.com, mattwu@....com
Subject: Re: [PATCH v6 3/4] kprobes: kretprobe scalability improvement with
 objpool

Hi Wuqiang,

On Tue,  8 Nov 2022 15:14:42 +0800
wuqiang <wuqiang.matt@...edance.com> wrote:

> kretprobe is using freelist to manage return-instances, but freelist,
> as LIFO queue based on singly linked list, scales badly and reduces
> the overall throughput of kretprobed routines, especially for high
> contention scenarios.
> 
> Here's a typical throughput test of sys_flock (counts in 10 seconds,
> measured with perf stat -a -I 10000 -e syscalls:sys_enter_flock):
> 
> OS: Debian 10 X86_64, Linux 6.1rc2
> HW: XEON 8336C x 2, 64 cores/128 threads, DDR4 3200MT/s
> 
>       1X       2X       4X       6X       8X      12X      16X
> 34762430 36546920 17949900 13101899 12569595 12646601 14729195
>      24X      32X      48X      64X      72X      96X     128X
> 19263546 10102064  8985418 11936495 11493980  7127789  9330985
> 
> This patch introduces objpool to kretprobe and rethook, with orginal
> freelist replaced and brings near-linear scalability to kretprobed
> routines. Tests of kretprobe throughput show the biggest ratio as
> 333.9x of the original freelist. Here's the comparison:
> 
>                   1X         2X         4X         8X        16X
> freelist:   34762430   36546920   17949900   12569595   14729195
> objpool:    35627544   72182095  144068494  287564688  576903916
>                  32X        48X        64X        96X       128X
> freelist:   10102064    8985418   11936495    7127789    9330985
> objpool:  1158876372 1737828164 2324371724 2380310472 2463182819
> 
> Tests on 96-core ARM64 system output similarly, but with the biggest
> ratio up to 642.2x:
> 
> OS: Debian 10 AARCH64, Linux 6.1rc2
> HW: Kunpeng-920 96 cores/2 sockets/4 NUMA nodes, DDR4 2933 MT/s
> 
>                   1X         2X         4X         8X        16X
> freelist:   17498299   10887037   10224710    8499132    6421751
> objpool:    18715726   35549845   71615884  144258971  283707220
>                  24X        32X        48X        64X        96X
> freelist:    5339868    4819116    3593919    3121575    2687167
> objpool:   419830913  571609748  877456139 1143316315 1725668029
> 
> Signed-off-by: wuqiang <wuqiang.matt@...edance.com>
> ---
>  include/linux/kprobes.h |  9 ++--
>  include/linux/rethook.h | 15 +++----
>  kernel/kprobes.c        | 95 +++++++++++++++++++----------------------
>  kernel/trace/fprobe.c   | 17 ++------
>  kernel/trace/rethook.c  | 80 +++++++++++++++++-----------------
>  5 files changed, 95 insertions(+), 121 deletions(-)
> 
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index a0b92be98984..f13f01e600c2 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -27,7 +27,7 @@
>  #include <linux/mutex.h>
>  #include <linux/ftrace.h>
>  #include <linux/refcount.h>
> -#include <linux/freelist.h>
> +#include <linux/objpool.h>
>  #include <linux/rethook.h>
>  #include <asm/kprobes.h>
>  
> @@ -141,6 +141,7 @@ static inline bool kprobe_ftrace(struct kprobe *p)
>   */
>  struct kretprobe_holder {
>  	struct kretprobe	*rp;
> +	struct objpool_head	oh;

Could you rename it to `pool` as rethook does?

>  	refcount_t		ref;
>  };
>  
> @@ -154,7 +155,6 @@ struct kretprobe {
>  #ifdef CONFIG_KRETPROBE_ON_RETHOOK
>  	struct rethook *rh;
>  #else
> -	struct freelist_head freelist;

OK, this is natural to move the head to kretprobe_holder, because
objpool must call its fini() function when all objects are freed.

>  	struct kretprobe_holder *rph;
>  #endif
>  };
> @@ -165,10 +165,7 @@ struct kretprobe_instance {
>  #ifdef CONFIG_KRETPROBE_ON_RETHOOK
>  	struct rethook_node node;
>  #else
> -	union {
> -		struct freelist_node freelist;
> -		struct rcu_head rcu;
> -	};
> +	struct rcu_head rcu;
>  	struct llist_node llist;
>  	struct kretprobe_holder *rph;
>  	kprobe_opcode_t *ret_addr;
> diff --git a/include/linux/rethook.h b/include/linux/rethook.h
> index c8ac1e5afcd1..278ec65e71fe 100644
> --- a/include/linux/rethook.h
> +++ b/include/linux/rethook.h
> @@ -6,7 +6,7 @@
>  #define _LINUX_RETHOOK_H
>  
>  #include <linux/compiler.h>
> -#include <linux/freelist.h>
> +#include <linux/objpool.h>
>  #include <linux/kallsyms.h>
>  #include <linux/llist.h>
>  #include <linux/rcupdate.h>
> @@ -30,14 +30,14 @@ typedef void (*rethook_handler_t) (struct rethook_node *, void *, struct pt_regs
>  struct rethook {
>  	void			*data;
>  	rethook_handler_t	handler;
> -	struct freelist_head	pool;
> +	struct objpool_head	pool;

On the other hand, the rethook already consolidated that "holder"
feature to itself, so you don't need to move, just replace the
freelist_head with objpool_head. LGTM.

>  	refcount_t		ref;
>  	struct rcu_head		rcu;
>  };
>  
>  /**
>   * struct rethook_node - The rethook shadow-stack entry node.
> - * @freelist: The freelist, linked to struct rethook::pool.
> + * @nod: The objpool node, linked to struct rethook::pool.

I don't see @nod in rethook_node. maybe a typo?

>   * @rcu: The rcu_head for deferred freeing.
>   * @llist: The llist, linked to a struct task_struct::rethooks.
>   * @rethook: The pointer to the struct rethook.
> @@ -48,19 +48,15 @@ struct rethook {
>   * on each entry of the shadow stack.
>   */
>  struct rethook_node {
> -	union {
> -		struct freelist_node freelist;
> -		struct rcu_head      rcu;
> -	};
> +	struct rcu_head		rcu;
>  	struct llist_node	llist;
>  	struct rethook		*rethook;
>  	unsigned long		ret_addr;
>  	unsigned long		frame;
>  };
>  
> -struct rethook *rethook_alloc(void *data, rethook_handler_t handler);
> +struct rethook *rethook_alloc(void *data, rethook_handler_t handler, gfp_t gfp, int size, int max);
>  void rethook_free(struct rethook *rh);
> -void rethook_add_node(struct rethook *rh, struct rethook_node *node);
>  struct rethook_node *rethook_try_get(struct rethook *rh);
>  void rethook_recycle(struct rethook_node *node);
>  void rethook_hook(struct rethook_node *node, struct pt_regs *regs, bool mcount);
> @@ -97,4 +93,3 @@ void rethook_flush_task(struct task_struct *tk);
>  #endif
>  
>  #endif
> -
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index cd9f5a66a690..a8b202f87e2d 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1865,10 +1865,12 @@ static struct notifier_block kprobe_exceptions_nb = {
>  static void free_rp_inst_rcu(struct rcu_head *head)
>  {
>  	struct kretprobe_instance *ri = container_of(head, struct kretprobe_instance, rcu);
> +	struct kretprobe_holder *rph = ri->rph;
>  
> -	if (refcount_dec_and_test(&ri->rph->ref))
> -		kfree(ri->rph);
> -	kfree(ri);
> +	if (refcount_dec_and_test(&rph->ref)) {
> +		objpool_fini(&rph->oh);
> +		kfree(rph);
> +	}
>  }
>  NOKPROBE_SYMBOL(free_rp_inst_rcu);
>  
> @@ -1877,7 +1879,7 @@ static void recycle_rp_inst(struct kretprobe_instance *ri)
>  	struct kretprobe *rp = get_kretprobe(ri);
>  
>  	if (likely(rp))
> -		freelist_add(&ri->freelist, &rp->freelist);
> +		objpool_push(ri, &rp->rph->oh);
>  	else
>  		call_rcu(&ri->rcu, free_rp_inst_rcu);
>  }
> @@ -1914,23 +1916,19 @@ NOKPROBE_SYMBOL(kprobe_flush_task);
>  
>  static inline void free_rp_inst(struct kretprobe *rp)
>  {
> -	struct kretprobe_instance *ri;
> -	struct freelist_node *node;
> -	int count = 0;
> -
> -	node = rp->freelist.head;
> -	while (node) {
> -		ri = container_of(node, struct kretprobe_instance, freelist);
> -		node = node->next;
> -
> -		kfree(ri);
> -		count++;
> -	}
> +	struct kretprobe_holder *rph = rp->rph;
> +	void *nod;
>  
> -	if (refcount_sub_and_test(count, &rp->rph->ref)) {
> -		kfree(rp->rph);
> -		rp->rph = NULL;
> -	}
> +	rp->rph = NULL;
> +	do {
> +		nod = objpool_pop(&rph->oh);
> +		/* deref anyway since we've one extra ref grabbed */
> +		if (refcount_dec_and_test(&rph->ref)) {
> +			objpool_fini(&rph->oh);
> +			kfree(rph);
> +			break;
> +		}
> +	} while (nod);
>  }
>  
>  /* This assumes the 'tsk' is the current task or the is not running. */
> @@ -2072,19 +2070,17 @@ NOKPROBE_SYMBOL(__kretprobe_trampoline_handler)
>  static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
>  {
>  	struct kretprobe *rp = container_of(p, struct kretprobe, kp);
> +	struct kretprobe_holder *rph = rp->rph;
>  	struct kretprobe_instance *ri;
> -	struct freelist_node *fn;
>  
> -	fn = freelist_try_get(&rp->freelist);
> -	if (!fn) {
> +	ri = objpool_pop(&rph->oh);
> +	if (!ri) {
>  		rp->nmissed++;
>  		return 0;
>  	}
>  
> -	ri = container_of(fn, struct kretprobe_instance, freelist);
> -
>  	if (rp->entry_handler && rp->entry_handler(ri, regs)) {
> -		freelist_add(&ri->freelist, &rp->freelist);
> +		objpool_push(ri, &rph->oh);
>  		return 0;
>  	}
>  
> @@ -2174,10 +2170,19 @@ int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long o
>  	return 0;
>  }
>  
> +#ifndef CONFIG_KRETPROBE_ON_RETHOOK
> +static int kretprobe_init_inst(void *context, void *nod)
> +{
> +	struct kretprobe_instance *ri = nod;
> +
> +	ri->rph = context;
> +	return 0;
> +}
> +#endif
> +
>  int register_kretprobe(struct kretprobe *rp)
>  {
>  	int ret;
> -	struct kretprobe_instance *inst;
>  	int i;
>  	void *addr;
>  
> @@ -2215,20 +2220,12 @@ int register_kretprobe(struct kretprobe *rp)
>  #endif
>  	}
>  #ifdef CONFIG_KRETPROBE_ON_RETHOOK
> -	rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler);
> +	rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler, GFP_KERNEL,
> +				sizeof(struct kretprobe_instance) + rp->data_size,
> +				rp->maxactive);
>  	if (!rp->rh)
>  		return -ENOMEM;
>  
> -	for (i = 0; i < rp->maxactive; i++) {
> -		inst = kzalloc(sizeof(struct kretprobe_instance) +
> -			       rp->data_size, GFP_KERNEL);
> -		if (inst == NULL) {
> -			rethook_free(rp->rh);
> -			rp->rh = NULL;
> -			return -ENOMEM;
> -		}
> -		rethook_add_node(rp->rh, &inst->node);
> -	}
>  	rp->nmissed = 0;
>  	/* Establish function entry probe point */
>  	ret = register_kprobe(&rp->kp);
> @@ -2237,25 +2234,19 @@ int register_kretprobe(struct kretprobe *rp)
>  		rp->rh = NULL;
>  	}
>  #else	/* !CONFIG_KRETPROBE_ON_RETHOOK */
> -	rp->freelist.head = NULL;
>  	rp->rph = kzalloc(sizeof(struct kretprobe_holder), GFP_KERNEL);
>  	if (!rp->rph)
>  		return -ENOMEM;
>  
> -	rp->rph->rp = rp;
> -	for (i = 0; i < rp->maxactive; i++) {
> -		inst = kzalloc(sizeof(struct kretprobe_instance) +
> -			       rp->data_size, GFP_KERNEL);
> -		if (inst == NULL) {
> -			refcount_set(&rp->rph->ref, i);
> -			free_rp_inst(rp);
> -			return -ENOMEM;
> -		}
> -		inst->rph = rp->rph;
> -		freelist_add(&inst->freelist, &rp->freelist);
> +	if (objpool_init(&rp->rph->oh, rp->maxactive, rp->maxactive,
> +			  rp->data_size + sizeof(struct kretprobe_instance),
> +			  GFP_KERNEL, rp->rph, kretprobe_init_inst, NULL)) {
> +		kfree(rp->rph);
> +		rp->rph = NULL;
> +		return -ENOMEM;
>  	}
> -	refcount_set(&rp->rph->ref, i);
> -
> +	refcount_set(&rp->rph->ref, rp->maxactive + 1);
> +	rp->rph->rp = rp;
>  	rp->nmissed = 0;
>  	/* Establish function entry probe point */
>  	ret = register_kprobe(&rp->kp);
> diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
> index e8143e368074..9a002bfbd216 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -125,7 +125,7 @@ static void fprobe_init(struct fprobe *fp)
>  
>  static int fprobe_init_rethook(struct fprobe *fp, int num)
>  {
> -	int i, size;
> +	int size;
>  
>  	if (num < 0)
>  		return -EINVAL;
> @@ -140,20 +140,11 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
>  	if (size < 0)
>  		return -E2BIG;
>  
> -	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
> +	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler, GFP_KERNEL,
> +				sizeof(struct fprobe_rethook_node), size);
>  	if (!fp->rethook)
>  		return -ENOMEM;
> -	for (i = 0; i < size; i++) {
> -		struct fprobe_rethook_node *node;
> -
> -		node = kzalloc(sizeof(*node), GFP_KERNEL);
> -		if (!node) {
> -			rethook_free(fp->rethook);
> -			fp->rethook = NULL;
> -			return -ENOMEM;
> -		}
> -		rethook_add_node(fp->rethook, &node->node);
> -	}
> +
>  	return 0;
>  }
>  
> diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> index c69d82273ce7..01df98db2fbe 100644
> --- a/kernel/trace/rethook.c
> +++ b/kernel/trace/rethook.c
> @@ -36,21 +36,17 @@ void rethook_flush_task(struct task_struct *tk)
>  static void rethook_free_rcu(struct rcu_head *head)
>  {
>  	struct rethook *rh = container_of(head, struct rethook, rcu);
> -	struct rethook_node *rhn;
> -	struct freelist_node *node;
> -	int count = 1;
> +	struct rethook_node *nod;
>  
> -	node = rh->pool.head;
> -	while (node) {
> -		rhn = container_of(node, struct rethook_node, freelist);
> -		node = node->next;
> -		kfree(rhn);
> -		count++;
> -	}
> -
> -	/* The rh->ref is the number of pooled node + 1 */
> -	if (refcount_sub_and_test(count, &rh->ref))
> -		kfree(rh);
> +	do {
> +		nod = objpool_pop(&rh->pool);
> +		/* deref anyway since we've one extra ref grabbed */
> +		if (refcount_dec_and_test(&rh->ref)) {
> +			objpool_fini(&rh->pool);
> +			kfree(rh);
> +			break;
> +		}
> +	} while (nod);
>  }
>  
>  /**
> @@ -70,16 +66,28 @@ void rethook_free(struct rethook *rh)
>  	call_rcu(&rh->rcu, rethook_free_rcu);
>  }
>  
> +static int rethook_init_node(void *context, void *nod)
> +{
> +	struct rethook_node *node = nod;
> +
> +	node->rethook = context;
> +	return 0;
> +}
> +
>  /**
>   * rethook_alloc() - Allocate struct rethook.
>   * @data: a data to pass the @handler when hooking the return.
>   * @handler: the return hook callback function.
> + * @gfp: default gfp for objpool allocation
> + * @size: rethook node size

@size should be @data_size, which is the size of additional data bytes
of rethook_node.

> + * @max: number of rethook nodes to be preallocated
>   *
>   * Allocate and initialize a new rethook with @data and @handler.
>   * Return NULL if memory allocation fails or @handler is NULL.
>   * Note that @handler == NULL means this rethook is going to be freed.
>   */
> -struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
> +struct rethook *rethook_alloc(void *data, rethook_handler_t handler, gfp_t gfp,
> +			      int size, int max)

This doesn't need @gfp. Just use GFP_KERNEL from rethook layer.

>  {
>  	struct rethook *rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);

And here, 

	if (data_size < 0 || max < 0)
		return -EINVAL;

>  
> @@ -88,34 +96,26 @@ struct rethook *rethook_alloc(void *data, rethook_handler_t handler)
>  
>  	rh->data = data;
>  	rh->handler = handler;
> -	rh->pool.head = NULL;
> -	refcount_set(&rh->ref, 1);
>  
> +	/* initialize the objpool for rethook nodes */
> +	if (objpool_init(&rh->pool, max, max, size, gfp, rh, rethook_init_node,
> +			NULL)) {
> +		kfree(rh);
> +		return NULL;
> +	}
> +	refcount_set(&rh->ref, max + 1);
>  	return rh;
>  }
>  
> -/**
> - * rethook_add_node() - Add a new node to the rethook.
> - * @rh: the struct rethook.
> - * @node: the struct rethook_node to be added.
> - *
> - * Add @node to @rh. User must allocate @node (as a part of user's
> - * data structure.) The @node fields are initialized in this function.
> - */
> -void rethook_add_node(struct rethook *rh, struct rethook_node *node)
> -{
> -	node->rethook = rh;
> -	freelist_add(&node->freelist, &rh->pool);
> -	refcount_inc(&rh->ref);
> -}
> -
>  static void free_rethook_node_rcu(struct rcu_head *head)
>  {
>  	struct rethook_node *node = container_of(head, struct rethook_node, rcu);
> +	struct rethook *rh = node->rethook;
>  
> -	if (refcount_dec_and_test(&node->rethook->ref))
> -		kfree(node->rethook);
> -	kfree(node);
> +	if (refcount_dec_and_test(&rh->ref)) {
> +		objpool_fini(&rh->pool);
> +		kfree(rh);
> +	}
>  }
>  
>  /**
> @@ -130,7 +130,7 @@ void rethook_recycle(struct rethook_node *node)
>  	lockdep_assert_preemption_disabled();
>  
>  	if (likely(READ_ONCE(node->rethook->handler)))
> -		freelist_add(&node->freelist, &node->rethook->pool);
> +		objpool_push(node, &node->rethook->pool);
>  	else
>  		call_rcu(&node->rcu, free_rethook_node_rcu);
>  }
> @@ -146,7 +146,7 @@ NOKPROBE_SYMBOL(rethook_recycle);
>  struct rethook_node *rethook_try_get(struct rethook *rh)
>  {
>  	rethook_handler_t handler = READ_ONCE(rh->handler);
> -	struct freelist_node *fn;
> +	struct rethook_node *nod;
>  
>  	lockdep_assert_preemption_disabled();
>  
> @@ -163,11 +163,11 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
>  	if (unlikely(!rcu_is_watching()))
>  		return NULL;
>  
> -	fn = freelist_try_get(&rh->pool);
> -	if (!fn)
> +	nod = (struct rethook_node *)objpool_pop(&rh->pool);
> +	if (!nod)
>  		return NULL;
>  
> -	return container_of(fn, struct rethook_node, freelist);
> +	return nod;

You can just write this part as

	return (struct rethook_node *)objpool_pop(&rh->pool);

Thank you,

>  }
>  NOKPROBE_SYMBOL(rethook_try_get);
>  
> -- 
> 2.34.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>

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