linux-kernel - [tip: core/rcu] printk: Prepare for nested printk_nmi

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Date:   Tue, 19 May 2020 19:52:37 -0000
From:   "tip-bot2 for Petr Mladek" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Petr Mladek <pmladek@...e.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: core/rcu] printk: Prepare for nested printk_nmi_enter()

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

Commit-ID:     8c4e93c362ff114def211d4629b120af86eb1275
Gitweb:        https://git.kernel.org/tip/8c4e93c362ff114def211d4629b120af86eb1275
Author:        Petr Mladek <pmladek@...e.com>
AuthorDate:    Mon, 24 Feb 2020 13:13:31 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Tue, 19 May 2020 15:51:16 +02:00

printk: Prepare for nested printk_nmi_enter()

There is plenty of space in the printk_context variable. Reserve one byte
there for the NMI context to be on the safe side.

It should never overflow. The BUG_ON(in_nmi() == NMI_MASK) in nmi_enter()
will trigger much earlier.

Signed-off-by: Petr Mladek <pmladek@...e.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@...cle.com>
Link: https://lkml.kernel.org/r/20200505134100.681374113@linutronix.de



---
 kernel/printk/internal.h    | 8 +++++---
 kernel/printk/printk_safe.c | 4 ++--
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index b2b0f52..660f9a6 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -6,9 +6,11 @@
 
 #ifdef CONFIG_PRINTK
 
-#define PRINTK_SAFE_CONTEXT_MASK	 0x3fffffff
-#define PRINTK_NMI_DIRECT_CONTEXT_MASK	 0x40000000
-#define PRINTK_NMI_CONTEXT_MASK		 0x80000000
+#define PRINTK_SAFE_CONTEXT_MASK	0x007ffffff
+#define PRINTK_NMI_DIRECT_CONTEXT_MASK	0x008000000
+#define PRINTK_NMI_CONTEXT_MASK		0xff0000000
+
+#define PRINTK_NMI_CONTEXT_OFFSET	0x010000000
 
 extern raw_spinlock_t logbuf_lock;
 
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index d9a659a..e8791f2 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -295,12 +295,12 @@ static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
 
 void notrace printk_nmi_enter(void)
 {
-	this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
+	this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
 }
 
 void notrace printk_nmi_exit(void)
 {
-	this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
+	this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
 }
 
 /*