Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Wed, 28 Dec 2022 00:59:35 +0900
From:   Masami Hiramatsu (Google) <mhiramat@kernel.org>
To:     wuqiang <wuqiang.matt@bytedance.com>
Cc:     davem@davemloft.net, anil.s.keshavamurthy@intel.com,
        naveen.n.rao@linux.ibm.com, rostedt@goodmis.org,
        peterz@infradead.org, akpm@linux-foundation.org,
        sander@svanheule.net, ebiggers@google.com,
        dan.j.williams@intel.com, jpoimboe@kernel.org,
        linux-kernel@vger.kernel.org, lkp@intel.com, mattwu@163.com
Subject: Re: [PATCH v7 3/5] kprobes: kretprobe scalability improvement with
 objpool
Message-Id: <20221228005935.d472211ea2c54c20fd87b2ef@kernel.org>
In-Reply-To: <20221212123153.190888-4-wuqiang.matt@bytedance.com>
References: <20221212123153.190888-1-wuqiang.matt@bytedance.com>
        <20221212123153.190888-4-wuqiang.matt@bytedance.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Precedence: bulk

Hi Matt,

On Mon, 12 Dec 2022 20:31:51 +0800
wuqiang <wuqiang.matt@bytedance.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

So for x86, the rethook is applied. And for arm64, kretprobes
is applied. OK, Looks good to me.

I have some comments below (but just nitpicks.)

> 
> Signed-off-by: wuqiang <wuqiang.matt@bytedance.com>

BTW, can you clarify your name on Signed-off-by? I see your name on
[5/5] that says "Matt Wu <wuqiang.matt@bytedance.com>". It should be
the same on Signed-off-by (and MODULE_AUTHOR) so that we can make sure
it is you.

> ---
>  include/linux/kprobes.h |   9 ++--
>  include/linux/rethook.h |  14 ++----
>  kernel/kprobes.c        | 101 +++++++++++++++++++---------------------
>  kernel/trace/fprobe.c   |  37 ++++++---------
>  kernel/trace/rethook.c  |  99 ++++++++++++++++++++-------------------
>  5 files changed, 118 insertions(+), 142 deletions(-)
> 
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index a0b92be98984..122b1f21f3a9 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	pool;
>  	refcount_t		ref;
>  };
>  
> @@ -154,7 +155,6 @@ struct kretprobe {
>  #ifdef CONFIG_KRETPROBE_ON_RETHOOK
>  	struct rethook *rh;
>  #else
> -	struct freelist_head freelist;
>  	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..f97283c622b7 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 +30,13 @@ 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;
>  	refcount_t		ref;
>  	struct rcu_head		rcu;
>  };
>  
>  /**
>   * struct rethook_node - The rethook shadow-stack entry node.
> - * @freelist: The freelist, linked to struct rethook::pool.
>   * @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 +47,15 @@ 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, int size, int num);
>  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 +92,3 @@ void rethook_flush_task(struct task_struct *tk);
>  #endif
>  
>  #endif
> -
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 3050631e528d..5f35997b61f7 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1868,13 +1868,28 @@ static struct notifier_block kprobe_exceptions_nb = {
>  #ifdef CONFIG_KRETPROBES
>  
>  #if !defined(CONFIG_KRETPROBE_ON_RETHOOK)
> +
> +/* callbacks for objpool of kretprobe instances */
> +static int kretprobe_init_inst(void *nod, void *context)
> +{
> +	struct kretprobe_instance *ri = nod;
> +
> +	ri->rph = context;
> +	return 0;
> +}
> +static int kretprobe_fini_pool(struct objpool_head *head, void *context)
> +{
> +	kfree(context);
> +	return 0;
> +}
> +
>  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->pool);
>  }
>  NOKPROBE_SYMBOL(free_rp_inst_rcu);
>  
> @@ -1883,7 +1898,7 @@ 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->pool);
>  	else
>  		call_rcu(&ri->rcu, free_rp_inst_rcu);
>  }
> @@ -1920,23 +1935,18 @@ 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->pool);
> +		/* deref anyway since we've one extra ref grabbed */
> +		if (refcount_dec_and_test(&rph->ref)) {
> +			objpool_fini(&rph->pool);
> +			break;
> +		}
> +	} while (nod);
>  }
>  
>  /* This assumes the 'tsk' is the current task or the is not running. */
> @@ -2078,19 +2088,17 @@ 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->pool);
> +	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->pool);
>  		return 0;
>  	}
>  
> @@ -2183,7 +2191,6 @@ int kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long o
>  int register_kretprobe(struct kretprobe *rp)
>  {
>  	int ret;
> -	struct kretprobe_instance *inst;
>  	int i;
>  	void *addr;
>  
> @@ -2221,20 +2228,12 @@ int register_kretprobe(struct kretprobe *rp)
>  #endif
>  	}
>  #ifdef CONFIG_KRETPROBE_ON_RETHOOK
> -	rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler);
> -	if (!rp->rh)
> -		return -ENOMEM;
> +	rp->rh = rethook_alloc((void *)rp, kretprobe_rethook_handler,
> +				sizeof(struct kretprobe_instance) +
> +				rp->data_size, rp->maxactive);
> +	if (IS_ERR(rp->rh))
> +		return PTR_ERR(rp->rh);
>  
> -	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);
> @@ -2243,25 +2242,19 @@ 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->pool, rp->maxactive, rp->data_size +
> +			sizeof(struct kretprobe_instance), GFP_KERNEL,
> +			rp->rph, kretprobe_init_inst, kretprobe_fini_pool)) {
> +		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..9b685d6921d1 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -125,41 +125,32 @@ static void fprobe_init(struct fprobe *fp)
>  
>  static int fprobe_init_rethook(struct fprobe *fp, int num)
>  {
> -	int i, size;
> -
> -	if (num < 0)
> -		return -EINVAL;
> +	int max;
>  
>  	if (!fp->exit_handler) {
>  		fp->rethook = NULL;
>  		return 0;
>  	}
>  
> -	/* Initialize rethook if needed */
> -	size = num * num_possible_cpus() * 2;
> -	if (size < 0)
> +	if (num <= 0)
> +		return -EINVAL;
> +	max = num * num_possible_cpus() * 2;
> +	/* Fail if max overflows */
> +	if (max <= 0)
>  		return -E2BIG;
>  
> -	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler);
> -	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);
> -	}
> +	/* Initialize rethook */
> +	fp->rethook = rethook_alloc((void *)fp, fprobe_exit_handler,
> +				sizeof(struct fprobe_rethook_node), max);
> +	if (IS_ERR(fp->rethook))
> +		return PTR_ERR(fp->rethook);
> +
>  	return 0;
>  }
>  
>  static void fprobe_fail_cleanup(struct fprobe *fp)
>  {
> -	if (fp->rethook) {
> +	if (!IS_ERR_OR_NULL(fp->rethook)) {
>  		/* Don't need to cleanup rethook->handler because this is not used. */
>  		rethook_free(fp->rethook);
>  		fp->rethook = NULL;
> @@ -313,7 +304,7 @@ int unregister_fprobe(struct fprobe *fp)
>  	 * current running handlers are finished, call unregister_ftrace_function()
>  	 * after this.
>  	 */
> -	if (fp->rethook)
> +	if (!IS_ERR_OR_NULL(fp->rethook))
>  		rethook_free(fp->rethook);
>  
>  	ret = unregister_ftrace_function(&fp->ops);
> diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> index 32c3dfdb4d6a..6e1014e4f2f7 100644
> --- a/kernel/trace/rethook.c
> +++ b/kernel/trace/rethook.c
> @@ -36,21 +36,16 @@ 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;
> -
> -	node = rh->pool.head;
> -	while (node) {
> -		rhn = container_of(node, struct rethook_node, freelist);
> -		node = node->next;
> -		kfree(rhn);
> -		count++;
> -	}
> +	struct rethook_node *nod;

Why 'nod' but not 'node'?

>  
> -	/* 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);
> +			break;
> +		}
> +	} while (nod);
>  }
>  
>  /**
> @@ -70,54 +65,65 @@ void rethook_free(struct rethook *rh)
>  	call_rcu(&rh->rcu, rethook_free_rcu);
>  }
>  
> +static int rethook_init_node(void *nod, void *context)
> +{
> +	struct rethook_node *node = nod;
> +
> +	node->rethook = context;
> +	return 0;
> +}
> +
> +static int rethook_fini_pool(struct objpool_head *head, void *context)
> +{
> +	kfree(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.
> + * @handler: the return hook callback function, must NOT be NULL
> + * @gfp: default gfp for objpool allocation

There is no @gfp in the function arguments.

> + * @size: node size: rethook node and additional data
> + * @num: 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.
> + * Return pointer of new rethook, or error codes for failures.
> + *
>   * 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,
> +			      int size, int num)
>  {
> -	struct rethook *rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);
> +	struct rethook *rh;
>  
> -	if (!rh || !handler) {
> -		kfree(rh);
> -		return NULL;
> -	}
> +	if (!handler || num <= 0 || size < sizeof(struct rethook_node))
> +		return ERR_PTR(-EINVAL);
> +
> +	rh = kzalloc(sizeof(struct rethook), GFP_KERNEL);
> +	if (!rh)
> +		return ERR_PTR(-ENOMEM);
>  
>  	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, num, size, GFP_KERNEL, rh,
> +			 rethook_init_node, rethook_fini_pool)) {
> +		kfree(rh);
> +		return ERR_PTR(-ENOMEM);
> +	}
> +	refcount_set(&rh->ref, num + 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);
>  }
>  
>  /**
> @@ -132,7 +138,7 @@ 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);
>  }
> @@ -148,7 +154,6 @@ 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;
>  
>  	lockdep_assert_preemption_disabled();
>  
> @@ -165,11 +170,7 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
>  	if (unlikely(!rcu_is_watching()))
>  		return NULL;
>  
> -	fn = freelist_try_get(&rh->pool);
> -	if (!fn)
> -		return NULL;
> -
> -	return container_of(fn, struct rethook_node, freelist);
> +	return (struct rethook_node *)objpool_pop(&rh->pool);
>  }
>  NOKPROBE_SYMBOL(rethook_try_get);
>  
> -- 
> 2.34.1
> 


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