[PATCH 6.12 098/265] uprobes: switch to RCU Tasks Trace flavor for better performance

Greg Kroah-Hartman
2026-03-12T20:17:59Z

From: Andrii Nakryiko <andrii@kernel.org>

[ Upstream commit 87195a1ee332add27bd51448c6b54aad551a28f5 ]

This patch switches uprobes SRCU usage to RCU Tasks Trace flavor, which
is optimized for more lightweight and quick readers (at the expense of
slower writers, which for uprobes is a fine tradeof) and has better
performance and scalability with number of CPUs.

Similarly to baseline vs SRCU, we've benchmarked SRCU-based
implementation vs RCU Tasks Trace implementation.

SRCU
====
uprobe-nop ( 1 cpus): 3.276 ± 0.005M/s ( 3.276M/s/cpu)
uprobe-nop ( 2 cpus): 4.125 ± 0.002M/s ( 2.063M/s/cpu)
uprobe-nop ( 4 cpus): 7.713 ± 0.002M/s ( 1.928M/s/cpu)
uprobe-nop ( 8 cpus): 8.097 ± 0.006M/s ( 1.012M/s/cpu)
uprobe-nop (16 cpus): 6.501 ± 0.056M/s ( 0.406M/s/cpu)
uprobe-nop (32 cpus): 4.398 ± 0.084M/s ( 0.137M/s/cpu)
uprobe-nop (64 cpus): 6.452 ± 0.000M/s ( 0.101M/s/cpu)

uretprobe-nop ( 1 cpus): 2.055 ± 0.001M/s ( 2.055M/s/cpu)
uretprobe-nop ( 2 cpus): 2.677 ± 0.000M/s ( 1.339M/s/cpu)
uretprobe-nop ( 4 cpus): 4.561 ± 0.003M/s ( 1.140M/s/cpu)
uretprobe-nop ( 8 cpus): 5.291 ± 0.002M/s ( 0.661M/s/cpu)
uretprobe-nop (16 cpus): 5.065 ± 0.019M/s ( 0.317M/s/cpu)
uretprobe-nop (32 cpus): 3.622 ± 0.003M/s ( 0.113M/s/cpu)
uretprobe-nop (64 cpus): 3.723 ± 0.002M/s ( 0.058M/s/cpu)

RCU Tasks Trace
===============
uprobe-nop ( 1 cpus): 3.396 ± 0.002M/s ( 3.396M/s/cpu)
uprobe-nop ( 2 cpus): 4.271 ± 0.006M/s ( 2.135M/s/cpu)
uprobe-nop ( 4 cpus): 8.499 ± 0.015M/s ( 2.125M/s/cpu)
uprobe-nop ( 8 cpus): 10.355 ± 0.028M/s ( 1.294M/s/cpu)
uprobe-nop (16 cpus): 7.615 ± 0.099M/s ( 0.476M/s/cpu)
uprobe-nop (32 cpus): 4.430 ± 0.007M/s ( 0.138M/s/cpu)
uprobe-nop (64 cpus): 6.887 ± 0.020M/s ( 0.108M/s/cpu)

uretprobe-nop ( 1 cpus): 2.174 ± 0.001M/s ( 2.174M/s/cpu)
uretprobe-nop ( 2 cpus): 2.853 ± 0.001M/s ( 1.426M/s/cpu)
uretprobe-nop ( 4 cpus): 4.913 ± 0.002M/s ( 1.228M/s/cpu)
uretprobe-nop ( 8 cpus): 5.883 ± 0.002M/s ( 0.735M/s/cpu)
uretprobe-nop (16 cpus): 5.147 ± 0.001M/s ( 0.322M/s/cpu)
uretprobe-nop (32 cpus): 3.738 ± 0.008M/s ( 0.117M/s/cpu)
uretprobe-nop (64 cpus): 4.397 ± 0.002M/s ( 0.069M/s/cpu)

Peak throughput for uprobes increases from 8 mln/s to 10.3 mln/s
(+28%!), and for uretprobes from 5.3 mln/s to 5.8 mln/s (+11%), as we
have more work to do on uretprobes side.

Even single-thread (no contention) performance is slightly better: 3.276
mln/s to 3.396 mln/s (+3.5%) for uprobes, and 2.055 mln/s to 2.174 mln/s
(+5.8%) for uretprobes.

We also select TASKS_TRACE_RCU for UPROBES in Kconfig due to the new
dependency.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Link: https://lkml.kernel.org/r/20240910174312.3646590-1-andrii@kernel.org
Stable-dep-of: a56a38fd9196 ("uprobes: Fix incorrect lockdep condition in filter_chain()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/Kconfig | 1 +
kernel/events/uprobes.c | 38 ++++++++++++++++----------------------
2 files changed, 17 insertions(+), 22 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 593452b43dd49..1812e4e4d7147 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -135,6 +135,7 @@ config KPROBES_ON_FTRACE
config UPROBES
def_bool n
depends on ARCH_SUPPORTS_UPROBES
+ select TASKS_TRACE_RCU
help
Uprobes is the user-space counterpart to kprobes: they
enable instrumentation applications (such as 'perf probe')
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index e30c4dd345f40..0eb9befe49a3c 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -26,6 +26,7 @@
#include <linux/task_work.h>
#include <linux/shmem_fs.h>
#include <linux/khugepaged.h>
+#include <linux/rcupdate_trace.h>

#include <linux/uprobes.h>

@@ -42,8 +43,6 @@ static struct rb_root uprobes_tree = RB_ROOT;
static DEFINE_RWLOCK(uprobes_treelock); /* serialize rbtree access */
static seqcount_rwlock_t uprobes_seqcount = SEQCNT_RWLOCK_ZERO(uprobes_seqcount, &uprobes_treelock);

-DEFINE_STATIC_SRCU(uprobes_srcu);
-
#define UPROBES_HASH_SZ 13
/* serialize uprobe->pending_list */
static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
@@ -667,7 +666,7 @@ static void put_uprobe(struct uprobe *uprobe)
delayed_uprobe_remove(uprobe, NULL);
mutex_unlock(&delayed_uprobe_lock);

- call_srcu(&uprobes_srcu, &uprobe->rcu, uprobe_free_rcu);
+ call_rcu_tasks_trace(&uprobe->rcu, uprobe_free_rcu);
}

static __always_inline
@@ -722,7 +721,7 @@ static struct uprobe *find_uprobe_rcu(struct inode *inode, loff_t offset)
struct rb_node *node;
unsigned int seq;

- lockdep_assert(srcu_read_lock_held(&uprobes_srcu));
+ lockdep_assert(rcu_read_lock_trace_held());

do {
seq = read_seqcount_begin(&uprobes_seqcount);
@@ -950,8 +949,7 @@ static bool filter_chain(struct uprobe *uprobe, struct mm_struct *mm)
bool ret = false;

down_read(&uprobe->consumer_rwsem);
- list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
- srcu_read_lock_held(&uprobes_srcu)) {
+ list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
ret = consumer_filter(uc, mm);
if (ret)
break;
@@ -1172,7 +1170,7 @@ void uprobe_unregister_sync(void)
* unlucky enough caller can free consumer's memory and cause
* handler_chain() or handle_uretprobe_chain() to do an use-after-free.
*/
- synchronize_srcu(&uprobes_srcu);
+ synchronize_rcu_tasks_trace();
}
EXPORT_SYMBOL_GPL(uprobe_unregister_sync);

@@ -1256,19 +1254,18 @@ EXPORT_SYMBOL_GPL(uprobe_register);
int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool add)
{
struct uprobe_consumer *con;
- int ret = -ENOENT, srcu_idx;
+ int ret = -ENOENT;

down_write(&uprobe->register_rwsem);

- srcu_idx = srcu_read_lock(&uprobes_srcu);
- list_for_each_entry_srcu(con, &uprobe->consumers, cons_node,
- srcu_read_lock_held(&uprobes_srcu)) {
+ rcu_read_lock_trace();
+ list_for_each_entry_rcu(con, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
if (con == uc) {
ret = register_for_each_vma(uprobe, add ? uc : NULL);
break;
}
}
- srcu_read_unlock(&uprobes_srcu, srcu_idx);
+ rcu_read_unlock_trace();

up_write(&uprobe->register_rwsem);

@@ -2150,8 +2147,7 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)

current->utask->auprobe = &uprobe->arch;

- list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
- srcu_read_lock_held(&uprobes_srcu)) {
+ list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
int rc = 0;

if (uc->handler) {
@@ -2189,15 +2185,13 @@ handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
{
struct uprobe *uprobe = ri->uprobe;
struct uprobe_consumer *uc;
- int srcu_idx;

- srcu_idx = srcu_read_lock(&uprobes_srcu);
- list_for_each_entry_srcu(uc, &uprobe->consumers, cons_node,
- srcu_read_lock_held(&uprobes_srcu)) {
+ rcu_read_lock_trace();
+ list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
if (uc->ret_handler)
uc->ret_handler(uc, ri->func, regs);
}
- srcu_read_unlock(&uprobes_srcu, srcu_idx);
+ rcu_read_unlock_trace();
}

static struct return_instance *find_next_ret_chain(struct return_instance *ri)
@@ -2282,13 +2276,13 @@ static void handle_swbp(struct pt_regs *regs)
{
struct uprobe *uprobe;
unsigned long bp_vaddr;
- int is_swbp, srcu_idx;
+ int is_swbp;

bp_vaddr = uprobe_get_swbp_addr(regs);
if (bp_vaddr == uprobe_get_trampoline_vaddr())
return uprobe_handle_trampoline(regs);

- srcu_idx = srcu_read_lock(&uprobes_srcu);
+ rcu_read_lock_trace();

uprobe = find_active_uprobe_rcu(bp_vaddr, &is_swbp);
if (!uprobe) {
@@ -2353,7 +2347,7 @@ static void handle_swbp(struct pt_regs *regs)

out:
/* arch_uprobe_skip_sstep() succeeded, or restart if can't singlestep */
- srcu_read_unlock(&uprobes_srcu, srcu_idx);
+ rcu_read_unlock_trace();
}

/*
--
2.51.0