linux-kernel - [PATCH] powerpc/smp: poll cpu_callin_map more aggressively in __cpu

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-next>] [day] [month] [year] [list]

Message-Id: <20220125072103.70715-1-nathanl@linux.ibm.com>
Date:   Tue, 25 Jan 2022 01:21:03 -0600
From:   Nathan Lynch <nathanl@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, mpe@...erman.id.au,
        npiggin@...il.com, brking@...ux.ibm.com, srikar@...ux.vnet.ibm.com
Subject: [PATCH] powerpc/smp: poll cpu_callin_map more aggressively in __cpu_up()

Replace the outdated iteration and timeout calculations here with
indefinite spin_until_cond()-wrapped poll of cpu_callin_map. __cpu_up()
already does this when waiting for the cpu to set its online bit before
returning, so this change is not really making the function more brittle.

Removing the msleep(1) in the hotplug path here reduces the time it takes
to online a CPU on a P9 PowerVM LPAR from about 30ms to 1ms when exercised
via thaw_secondary_cpus().

Signed-off-by: Nathan Lynch <nathanl@...ux.ibm.com>
---
 arch/powerpc/kernel/smp.c | 25 ++-----------------------
 1 file changed, 2 insertions(+), 23 deletions(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index b7fd6a72aa76..990893365fe0 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -1270,7 +1270,7 @@ static void cpu_idle_thread_init(unsigned int cpu, struct task_struct *idle)
 
 int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
-	int rc, c;
+	int rc;
 
 	/*
 	 * Don't allow secondary threads to come online if inhibited
@@ -1314,28 +1314,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle)
 		return rc;
 	}
 
-	/*
-	 * wait to see if the cpu made a callin (is actually up).
-	 * use this value that I found through experimentation.
-	 * -- Cort
-	 */
-	if (system_state < SYSTEM_RUNNING)
-		for (c = 50000; c && !cpu_callin_map[cpu]; c--)
-			udelay(100);
-#ifdef CONFIG_HOTPLUG_CPU
-	else
-		/*
-		 * CPUs can take much longer to come up in the
-		 * hotplug case.  Wait five seconds.
-		 */
-		for (c = 5000; c && !cpu_callin_map[cpu]; c--)
-			msleep(1);
-#endif
-
-	if (!cpu_callin_map[cpu]) {
-		printk(KERN_ERR "Processor %u is stuck.\n", cpu);
-		return -ENOENT;
-	}
+	spin_until_cond(cpu_callin_map[cpu] != 0);
 
 	DBG("Processor %u found.\n", cpu);
 
-- 
2.34.1