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

From: wuqiang.matt
Date: Mon Oct 16 2023 - 11:18:30 EST

On 2023/10/16 21:21, Masami Hiramatsu (Google) wrote:
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.

Got it. Would these 2 fixes catch the release window of v6.6 ?


Thanks!