[patch V4 part 1 26/36] printk: Prepare for nested printk_nmi_enter()

Thomas Gleixner
2020-05-05T14:14:13Z

From: Petr Mladek <pmladek@suse.com>

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@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200224121331.tnkvp6mmjchm4s2i@pathway.suse.cz
---
kernel/printk/internal.h | 8 +++++---
kernel/printk/printk_safe.c | 4 ++--
2 files changed, 7 insertions(+), 5 deletions(-)

--- 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;

--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -295,12 +295,12 @@ static __printf(1, 0) int vprintk_nmi(co

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);
}

/*