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Date: Mon, 14 Aug 2017 09:21:34 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Larry Finger <Larry.Finger@lwfinger.net>
cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: Regression in kernel 4.13-rcX for 32-bit x86 system - bisected
 to commit fc8dffd379ca
In-Reply-To: <0e25aebb-b501-b92b-3931-1646b009e8ef@lwfinger.net>
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References: <0e25aebb-b501-b92b-3931-1646b009e8ef@lwfinger.net>
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On Mon, 14 Aug 2017, Larry Finger wrote:

> My Del Latitude D600 (single 32-bit CPU) shows the following locking message
> when booted:
> 
> ============================================
> WARNING: possible recursive locking detected
> 4.12.0-rc2-00029-gfc8dffd #159 Not tainted
> --------------------------------------------
> systemd-udevd/153 is trying to acquire lock:
>  (cpu_hotplug_lock.rw_sem){.+.+.+}, at: [<c030fc26>] stop_machine+0x16/0x30
> 
> but task is already holding lock:
>  (cpu_hotplug_lock.rw_sem){.+.+.+}, at: [<c0234353>] mtrr_add_page+0x83/0x470

....

>  cpus_read_lock+0x48/0x90
>  ? stop_machine+0x16/0x30
>  stop_machine+0x16/0x30
>  mtrr_add_page+0x18b/0x470
>  mtrr_add+0x3e/0x70
 
> This problem was bisected to commit fc8dffd379ca ("cpu/hotplug: Convert
> hotplug locking to percpu rwsem"). I am very confident in the correctness of
> the bisection.

Fix below.

Thanks,

	tglx

8<--------------------

diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index c5bb63be4ba1..40d5a8a75212 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -237,6 +237,18 @@ set_mtrr(unsigned int reg, unsigned long base, unsigned long size, mtrr_type typ
 	stop_machine(mtrr_rendezvous_handler, &data, cpu_online_mask);
 }
 
+static void set_mtrr_cpuslocked(unsigned int reg, unsigned long base,
+				unsigned long size, mtrr_type type)
+{
+	struct set_mtrr_data data = { .smp_reg = reg,
+				      .smp_base = base,
+				      .smp_size = size,
+				      .smp_type = type
+				    };
+
+	stop_machine_cpuslocked(mtrr_rendezvous_handler, &data, cpu_online_mask);
+}
+
 static void set_mtrr_from_inactive_cpu(unsigned int reg, unsigned long base,
 				      unsigned long size, mtrr_type type)
 {
@@ -370,7 +382,7 @@ int mtrr_add_page(unsigned long base, unsigned long size,
 	/* Search for an empty MTRR */
 	i = mtrr_if->get_free_region(base, size, replace);
 	if (i >= 0) {
-		set_mtrr(i, base, size, type);
+		set_mtrr_cpuslocked(i, base, size, type);
 		if (likely(replace < 0)) {
 			mtrr_usage_table[i] = 1;
 		} else {
@@ -378,7 +390,7 @@ int mtrr_add_page(unsigned long base, unsigned long size,
 			if (increment)
 				mtrr_usage_table[i]++;
 			if (unlikely(replace != i)) {
-				set_mtrr(replace, 0, 0, 0);
+				set_mtrr_cpuslocked(replace, 0, 0, 0);
 				mtrr_usage_table[replace] = 0;
 			}
 		}
@@ -506,7 +518,7 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
 		goto out;
 	}
 	if (--mtrr_usage_table[reg] < 1)
-		set_mtrr(reg, 0, 0, 0);
+		set_mtrr_cpuslocked(reg, 0, 0, 0);
 	error = reg;
  out:
 	mutex_unlock(&mtrr_mutex);