linux-kernel - [PATCH 5.17 005/140] Revert "parisc: Mark cr16 CPU clocksource unstable on all SMP machines"

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

Message-Id: <20220510130741.760254485@linuxfoundation.org>
Date:   Tue, 10 May 2022 15:06:35 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Helge Deller <deller@....de>,
        John David Anglin <dave.anglin@...l.net>
Subject: [PATCH 5.17 005/140] Revert "parisc: Mark cr16 CPU clocksource unstable on all SMP machines"

From: Helge Deller <deller@....de>

commit 9dc4241bb14afecd16518a0760bceb3d7359b12a upstream.

This reverts commit afdb4a5b1d340e4afffc65daa21cc71890d7d589.

It triggers RCU stalls at boot with a 32-bit kernel.

Signed-off-by: Helge Deller <deller@....de>
Noticed-by: John David Anglin <dave.anglin@...l.net>
Cc: stable@...r.kernel.org # v5.16+
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/parisc/kernel/time.c |   28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

--- a/arch/parisc/kernel/time.c
+++ b/arch/parisc/kernel/time.c
@@ -249,16 +249,30 @@ void __init time_init(void)
 static int __init init_cr16_clocksource(void)
 {
 	/*
-	 * The cr16 interval timers are not syncronized across CPUs, even if
-	 * they share the same socket.
+	 * The cr16 interval timers are not syncronized across CPUs on
+	 * different sockets, so mark them unstable and lower rating on
+	 * multi-socket SMP systems.
 	 */
 	if (num_online_cpus() > 1 && !running_on_qemu) {
-		/* mark sched_clock unstable */
-		clear_sched_clock_stable();
+		int cpu;
+		unsigned long cpu0_loc;
+		cpu0_loc = per_cpu(cpu_data, 0).cpu_loc;
 
-		clocksource_cr16.name = "cr16_unstable";
-		clocksource_cr16.flags = CLOCK_SOURCE_UNSTABLE;
-		clocksource_cr16.rating = 0;
+		for_each_online_cpu(cpu) {
+			if (cpu == 0)
+				continue;
+			if ((cpu0_loc != 0) &&
+			    (cpu0_loc == per_cpu(cpu_data, cpu).cpu_loc))
+				continue;
+
+			/* mark sched_clock unstable */
+			clear_sched_clock_stable();
+
+			clocksource_cr16.name = "cr16_unstable";
+			clocksource_cr16.flags = CLOCK_SOURCE_UNSTABLE;
+			clocksource_cr16.rating = 0;
+			break;
+		}
 	}
 
 	/* register at clocksource framework */