Re: [PATCH v10 3/5] kprobes: kretprobe scalability improvement with objpool

From: Google
Date: Mon Oct 16 2023 - 09:21:15 EST

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On Sun, 15 Oct 2023 13:32:49 +0800
"wuqiang.matt" <wuqiang.matt@xxxxxxxxxxxxx> 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_prctl (counts in 10 seconds,
> measured with perf stat -a -I 10000 -e syscalls:sys_enter_prctl):
>
> OS: Debian 10 X86_64, Linux 6.5rc7 with freelist
> HW: XEON 8336C x 2, 64 cores/128 threads, DDR4 3200MT/s
>
> 1T 2T 4T 8T 16T 24T
> 24150045 29317964 15446741 12494489 18287272 17708768
> 32T 48T 64T 72T 96T 128T
> 16200682 13737658 11645677 11269858 10470118 9931051
>
> This patch introduces objpool to replace freelist. objpool is a
> high performance queue, which can bring near-linear scalability
> to kretprobed routines. Tests of kretprobe throughput show the
> biggest ratio as 159x of original freelist. Here's the result:
>
> 1T 2T 4T 8T 16T
> native: 41186213 82336866 164250978 328662645 658810299
> freelist: 24150045 29317964 15446741 12494489 18287272
> objpool: 23926730 48010314 96125218 191782984 385091769
> 32T 48T 64T 96T 128T
> native: 1330338351 1969957941 2512291791 1514690434 2671040914
> freelist: 16200682 13737658 11645677 10470118 9931051
> objpool: 764481096 1147149781 1456220214 1502109662 1579015050
>
> Testings on 96-core ARM64 output similarly, but with the biggest
> ratio up to 336x:
>
> OS: Debian 10 AARCH64, Linux 6.5rc7
> HW: Kunpeng-920 96 cores/2 sockets/4 NUMA nodes, DDR4 2933 MT/s
>
> 1T 2T 4T 8T 16T
> native: . 30066096 63569843 126194076 257447289 505800181
> freelist: 16152090 11064397 11124068 7215768 5663013
> objpool: 13997541 28032100 55726624 110099926 221498787
> 24T 32T 48T 64T 96T
> native: 763305277 1015925192 1521075123 2033009392 3021013752
> freelist: 5015810 4602893 3766792 3382478 2945292
> objpool: 328192025 439439564 668534502 887401381 990067903
>
> Signed-off-by: wuqiang.matt <wuqiang.matt@xxxxxxxxxxxxx>
> ---
> include/linux/kprobes.h | 11 ++---
> include/linux/rethook.h | 16 ++-----
> kernel/kprobes.c | 93 +++++++++++++++++------------------------
> kernel/trace/fprobe.c | 32 ++++++--------
> kernel/trace/rethook.c | 90 ++++++++++++++++++---------------------
> 5 files changed, 98 insertions(+), 144 deletions(-)
>
> diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
> index 85a64cb95d75..365eb092e9c4 100644
> --- a/include/linux/kprobes.h
> +++ b/include/linux/kprobes.h
> @@ -26,8 +26,7 @@
> #include <linux/rcupdate.h>
> #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>
>
> @@ -141,7 +140,7 @@ static inline bool kprobe_ftrace(struct kprobe *p)
> */
> struct kretprobe_holder {
> struct kretprobe *rp;
> - refcount_t ref;
> + struct objpool_head pool;
> };
>
> struct kretprobe {
> @@ -154,7 +153,6 @@ struct kretprobe {
> #ifdef CONFIG_KRETPROBE_ON_RETHOOK
> struct rethook *rh;
> #else
> - struct freelist_head freelist;
> struct kretprobe_holder *rph;
> #endif
> };
> @@ -165,10 +163,7 @@ 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 26b6f3c81a76..ce69b2b7bc35 100644
> --- a/include/linux/rethook.h
> +++ b/include/linux/rethook.h
> @@ -6,11 +6,10 @@
> #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>
> -#include <linux/refcount.h>
>
> struct rethook_node;
>
> @@ -30,14 +29,12 @@ typedef void (*rethook_handler_t) (struct rethook_node *, void *, unsigned long,
> struct rethook {
> void *data;
> rethook_handler_t handler;
> - struct freelist_head pool;
> - refcount_t ref;
> + struct objpool_head pool;
> 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.
> @@ -48,20 +45,16 @@ 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_stop(struct rethook *rh);
> 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);
> @@ -98,4 +91,3 @@ void rethook_flush_task(struct task_struct *tk);
> #endif
>
> #endif
> -
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index ca385b61d546..075a632e6c7c 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1877,13 +1877,27 @@ 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);
> + objpool_drop(ri, &rph->pool);
> }
> NOKPROBE_SYMBOL(free_rp_inst_rcu);
>
> @@ -1892,7 +1906,7 @@ 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);
> }
> @@ -1929,23 +1943,12 @@ 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;
>
> - if (refcount_sub_and_test(count, &rp->rph->ref)) {
> - kfree(rp->rph);
> - rp->rph = NULL;
> - }
> + if (!rph)
> + return;
> + rp->rph = NULL;
> + objpool_fini(&rph->pool);
> }
>
> /* This assumes the 'tsk' is the current task or the is not running. */
> @@ -2087,19 +2090,17 @@ 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;
> }
>
> @@ -2193,7 +2194,6 @@ 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;
>
> @@ -2227,19 +2227,12 @@ int register_kretprobe(struct kretprobe *rp)
> rp->maxactive = max_t(unsigned int, 10, 2*num_possible_cpus());
>
> #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(struct_size(inst, data, 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);
> @@ -2249,24 +2241,18 @@ 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(struct_size(inst, data, 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);
> -
> + 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 3b21f4063258..f5bf98e6b2ac 100644
> --- a/kernel/trace/fprobe.c
> +++ b/kernel/trace/fprobe.c
> @@ -187,9 +187,9 @@ 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)
> + if (num <= 0)
> return -EINVAL;

Oops, this must be a bugfix. Let me fix it.

>
> if (!fp->exit_handler) {
> @@ -202,29 +202,21 @@ static int fprobe_init_rethook(struct fprobe *fp, int num)
> size = fp->nr_maxactive;
> else
> size = num * num_possible_cpus() * 2;
> - if (size < 0)
> + if (size <= 0)
> return -E2BIG;

Here too.

Except for this point, it looks good to me.

Thanks!

--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

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