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-rw-r--r--kernel/printk/internal.h6
-rw-r--r--kernel/printk/printk.c19
-rw-r--r--kernel/printk/printk_safe.c26
-rw-r--r--lib/nmi_backtrace.c3
4 files changed, 45 insertions, 9 deletions
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 1db044f808b7..2a7d04049af4 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -18,12 +18,14 @@
#ifdef CONFIG_PRINTK
-#define PRINTK_SAFE_CONTEXT_MASK 0x7fffffff
-#define PRINTK_NMI_CONTEXT_MASK 0x80000000
+#define PRINTK_SAFE_CONTEXT_MASK 0x3fffffff
+#define PRINTK_NMI_DEFERRED_CONTEXT_MASK 0x40000000
+#define PRINTK_NMI_CONTEXT_MASK 0x80000000
extern raw_spinlock_t logbuf_lock;
__printf(1, 0) int vprintk_default(const char *fmt, va_list args);
+__printf(1, 0) int vprintk_deferred(const char *fmt, va_list args);
__printf(1, 0) int vprintk_func(const char *fmt, va_list args);
void __printk_safe_enter(void);
void __printk_safe_exit(void);
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 779479ac9f57..e5278e7d1922 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2722,16 +2722,13 @@ void wake_up_klogd(void)
preempt_enable();
}
-int printk_deferred(const char *fmt, ...)
+int vprintk_deferred(const char *fmt, va_list args)
{
- va_list args;
int r;
- preempt_disable();
- va_start(args, fmt);
r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args);
- va_end(args);
+ preempt_disable();
__this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
preempt_enable();
@@ -2739,6 +2736,18 @@ int printk_deferred(const char *fmt, ...)
return r;
}
+int printk_deferred(const char *fmt, ...)
+{
+ va_list args;
+ int r;
+
+ va_start(args, fmt);
+ r = vprintk_deferred(fmt, args);
+ va_end(args);
+
+ return r;
+}
+
/*
* printk rate limiting, lifted from the networking subsystem.
*
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 033e50a7d706..03a42a539b20 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -308,12 +308,24 @@ static int vprintk_nmi(const char *fmt, va_list args)
void printk_nmi_enter(void)
{
- this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
+ /*
+ * The size of the extra per-CPU buffer is limited. Use it only when
+ * the main one is locked. If this CPU is not in the safe context,
+ * the lock must be taken on another CPU and we could wait for it.
+ */
+ if ((this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK) &&
+ raw_spin_is_locked(&logbuf_lock)) {
+ this_cpu_or(printk_context, PRINTK_NMI_CONTEXT_MASK);
+ } else {
+ this_cpu_or(printk_context, PRINTK_NMI_DEFERRED_CONTEXT_MASK);
+ }
}
void printk_nmi_exit(void)
{
- this_cpu_and(printk_context, ~PRINTK_NMI_CONTEXT_MASK);
+ this_cpu_and(printk_context,
+ ~(PRINTK_NMI_CONTEXT_MASK |
+ PRINTK_NMI_DEFERRED_CONTEXT_MASK));
}
#else
@@ -351,12 +363,22 @@ void __printk_safe_exit(void)
__printf(1, 0) int vprintk_func(const char *fmt, va_list args)
{
+ /* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
return vprintk_nmi(fmt, args);
+ /* Use extra buffer to prevent a recursion deadlock in safe mode. */
if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
return vprintk_safe(fmt, args);
+ /*
+ * Use the main logbuf when logbuf_lock is available in NMI.
+ * But avoid calling console drivers that might have their own locks.
+ */
+ if (this_cpu_read(printk_context) & PRINTK_NMI_DEFERRED_CONTEXT_MASK)
+ return vprintk_deferred(fmt, args);
+
+ /* No obstacles. */
return vprintk_default(fmt, args);
}
diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
index 4e8a30d1c22f..0bc0a3535a8a 100644
--- a/lib/nmi_backtrace.c
+++ b/lib/nmi_backtrace.c
@@ -86,9 +86,11 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
bool nmi_cpu_backtrace(struct pt_regs *regs)
{
+ static arch_spinlock_t lock = __ARCH_SPIN_LOCK_UNLOCKED;
int cpu = smp_processor_id();
if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
+ arch_spin_lock(&lock);
if (regs && cpu_in_idle(instruction_pointer(regs))) {
pr_warn("NMI backtrace for cpu %d skipped: idling at pc %#lx\n",
cpu, instruction_pointer(regs));
@@ -99,6 +101,7 @@ bool nmi_cpu_backtrace(struct pt_regs *regs)
else
dump_stack();
}
+ arch_spin_unlock(&lock);
cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
return true;
}