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Date: Mon, 16 Oct 2023 23:18:09 +0800
From: "wuqiang.matt" <wuqiang.matt@...edance.com>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: linux-trace-kernel@...r.kernel.org, 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 v10 3/5] kprobes: kretprobe scalability improvement with
objpool
On 2023/10/16 21:21, Masami Hiramatsu (Google) wrote:
> On Sun, 15 Oct 2023 13:32:49 +0800
> "wuqiang.matt" <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_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@...edance.com>
>> ---
>> 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.
Got it. Would these 2 fixes catch the release window of v6.6 ?
>
> Thanks!
>
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