linux-kernel - [PATCH] rcu: Let rcu_dump_task() be used without preemption disabled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date: Fri, 28 Jun 2024 13:18:26 +0900
From: takakura@...inux.co.jp
To: paulmck@...nel.org,
	frederic@...nel.org,
	neeraj.upadhyay@...nel.org,
	joel@...lfernandes.org,
	josh@...htriplett.org,
	boqun.feng@...il.com,
	rostedt@...dmis.org,
	mathieu.desnoyers@...icios.com,
	jiangshanlai@...il.com,
	qiang.zhang1211@...il.com,
	mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org,
	dietmar.eggemann@....com,
	bsegall@...gle.com,
	mgorman@...e.de,
	bristot@...hat.com,
	vschneid@...hat.com
Cc: rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Ryo Takakura <takakura@...inux.co.jp>
Subject: [PATCH] rcu: Let rcu_dump_task() be used without preemption disabled

From: Ryo Takakura <takakura@...inux.co.jp>

The commit 2d7f00b2f0130 ("rcu: Suppress smp_processor_id() complaint
in synchronize_rcu_expedited_wait()") disabled preemption around
dump_cpu_task() to suppress warning on its usage within preemtible context.

Calling dump_cpu_task() doesn't required to be in non-preemptible context
except for suppressing the smp_processor_id() warning.
As the smp_processor_id() is evaluated along with in_hardirq()
to check if it's in interrupt context, this patch removes the need
for its preemtion disablement by reordering the condition so that
smp_processor_id() only gets evaluated when it's in interrupt context.

Signed-off-by: Ryo Takakura <takakura@...inux.co.jp>
---
 kernel/rcu/tree_exp.h | 2 --
 kernel/sched/core.c   | 2 +-
 2 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 8a1d9c8bd9f7..80c461b26144 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -617,9 +617,7 @@ static void synchronize_rcu_expedited_wait(void)
 				mask = leaf_node_cpu_bit(rnp, cpu);
 				if (!(READ_ONCE(rnp->expmask) & mask))
 					continue;
-				preempt_disable(); // For smp_processor_id() in dump_cpu_task().
 				dump_cpu_task(cpu);
-				preempt_enable();
 			}
 			rcu_exp_print_detail_task_stall_rnp(rnp);
 		}
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bcf2c4cc0522..38efbdafe3d4 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -11485,7 +11485,7 @@ struct cgroup_subsys cpu_cgrp_subsys = {
 
 void dump_cpu_task(int cpu)
 {
-	if (cpu == smp_processor_id() && in_hardirq()) {
+	if (in_hardirq() && cpu == smp_processor_id()) {
 		struct pt_regs *regs;
 
 		regs = get_irq_regs();
-- 
2.34.1