linux-kernel - [tip: perf/core] uprobes: Remove the spinlock within handle

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Message-ID: <173858689713.10177.999351087906743555.tip-bot2@tip-bot2>
Date: Mon, 03 Feb 2025 12:48:17 -0000
From: "tip-bot2 for Liao Chang" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: perf/core] uprobes: Remove the spinlock within handle_singlestep()

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     a66396c911bd662d503de3ec8f0a140b1081bde7
Gitweb:        https://git.kernel.org/tip/a66396c911bd662d503de3ec8f0a140b1081bde7
Author:        Liao Chang <liaochang1@...wei.com>
AuthorDate:    Fri, 24 Jan 2025 09:38:26 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 03 Feb 2025 11:46:06 +01:00

uprobes: Remove the spinlock within handle_singlestep()

This patch introduces a flag to track TIF_SIGPENDING is suppress
temporarily during the uprobe single-step. Upon uprobe singlestep is
handled and the flag is confirmed, it could resume the TIF_SIGPENDING
directly without acquiring the siglock in most case, then reducing
contention and improving overall performance.

I've use the script developed by Andrii in [1] to run benchmark. The CPU
used was Kunpeng916 (Hi1616), 4 NUMA nodes, 64 cores@...GHz running the
kernel on next tree + the optimization for get_xol_insn_slot() [2].

before-opt
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20250124093826.2123675-3-liaochang1@huawei.com
---
 include/linux/uprobes.h | 1 +
 kernel/events/uprobes.c | 8 +++++---
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index b1df7d7..a40efdd 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -143,6 +143,7 @@ struct uprobe_task {
 
 	struct uprobe			*active_uprobe;
 	unsigned long			xol_vaddr;
+	bool				signal_denied;
 
 	struct arch_uprobe              *auprobe;
 };
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 33bd608..870f697 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -2302,6 +2302,7 @@ bool uprobe_deny_signal(void)
 	WARN_ON_ONCE(utask->state != UTASK_SSTEP);
 
 	if (task_sigpending(t)) {
+		utask->signal_denied = true;
 		clear_tsk_thread_flag(t, TIF_SIGPENDING);
 
 		if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) {
@@ -2735,9 +2736,10 @@ static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
 	utask->state = UTASK_RUNNING;
 	xol_free_insn_slot(utask);
 
-	spin_lock_irq(&current->sighand->siglock);
-	recalc_sigpending(); /* see uprobe_deny_signal() */
-	spin_unlock_irq(&current->sighand->siglock);
+	if (utask->signal_denied) {
+		set_thread_flag(TIF_SIGPENDING);
+		utask->signal_denied = false;
+	}
 
 	if (unlikely(err)) {
 		uprobe_warn(current, "execute the probed insn, sending SIGILL.");