From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Jiri Kosina <jkosina@suse.cz>, Michal Hocko <mhocko@suse.cz>,
Jan Kara <jack@suse.cz>, Frederic Weisbecker <fweisbec@gmail.com>,
Dave Anderson <anderson@redhat.com>,
Petr Mladek <pmladek@suse.cz>
Subject: [RFC][PATCH 3/3] x86/nmi: Perform a safe NMI stack trace on all CPUs
Date: Thu, 19 Jun 2014 17:33:32 -0400 [thread overview]
Message-ID: <20140619213952.360076309@goodmis.org> (raw)
In-Reply-To: 20140619213329.478113470@goodmis.org
[-- Attachment #1: 0003-x86-nmi-Perform-a-safe-NMI-stack-trace-on-all-CPUs.patch --]
[-- Type: text/plain, Size: 3704 bytes --]
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
When trigger_all_cpu_backtrace() is called on x86, it will trigger an
NMI on each CPU and call show_regs(). But this can lead to a hard lock
up if the NMI comes in on another printk().
In order to avoid this, when the NMI triggers, it switches the printk
routine for that CPU to call a NMI safe printk function that records the
printk in a per_cpu trace_seq descriptor. After all NMIs have finished
recording its data, the trace_seqs are printed in a safe context.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/kernel/apic/hw_nmi.c | 66 ++++++++++++++++++++++++++++++++++++++++---
1 file changed, 62 insertions(+), 4 deletions(-)
diff --git a/arch/x86/kernel/apic/hw_nmi.c b/arch/x86/kernel/apic/hw_nmi.c
index c3fcb5de5083..6731604bb1cd 100644
--- a/arch/x86/kernel/apic/hw_nmi.c
+++ b/arch/x86/kernel/apic/hw_nmi.c
@@ -18,6 +18,7 @@
#include <linux/nmi.h>
#include <linux/module.h>
#include <linux/delay.h>
+#include <linux/trace_seq.h>
#ifdef CONFIG_HARDLOCKUP_DETECTOR
u64 hw_nmi_get_sample_period(int watchdog_thresh)
@@ -30,11 +31,30 @@ u64 hw_nmi_get_sample_period(int watchdog_thresh)
/* For reliability, we're prepared to waste bits here. */
static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
+/* Safe printing in NMI context */
+static DEFINE_PER_CPU(struct trace_seq, nmi_print_seq);
+
/* "in progress" flag of arch_trigger_all_cpu_backtrace */
static unsigned long backtrace_flag;
+static void print_seq_line(struct trace_seq *s, int last, int pos)
+{
+ const char *buf = s->buffer + last;
+
+ /* Chop off the saved log level and update the length */
+ if (printk_get_level(buf)) {
+ buf += 2;
+ last += 2;
+ }
+
+ pr_emerg("%.*s", (pos - last) + 1, buf);
+}
+
void arch_trigger_all_cpu_backtrace(void)
{
+ struct trace_seq *s;
+ int len;
+ int cpu;
int i;
if (test_and_set_bit(0, &backtrace_flag))
@@ -44,6 +64,11 @@ void arch_trigger_all_cpu_backtrace(void)
*/
return;
+ for_each_possible_cpu(i) {
+ s = &per_cpu(nmi_print_seq, i);
+ trace_seq_init(s);
+ }
+
cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
printk(KERN_INFO "sending NMI to all CPUs:\n");
@@ -56,8 +81,39 @@ void arch_trigger_all_cpu_backtrace(void)
mdelay(1);
}
+ for_each_possible_cpu(cpu) {
+ int last_i = 0;
+
+ s = &per_cpu(nmi_print_seq, cpu);
+ len = s->len;
+ if (!len)
+ continue;
+
+ /* Print line by line. */
+ for (i = 0; i < len; i++) {
+ if (s->buffer[i] == '\n') {
+ print_seq_line(s, last_i, i);
+ last_i = i + 1;
+ }
+ }
+ if (last_i < i - 1) {
+ print_seq_line(s, last_i, i);
+ pr_cont("\n");
+ }
+ }
+
clear_bit(0, &backtrace_flag);
smp_mb__after_atomic();
+ return true;
+}
+
+static int nmi_vprintk(const char *fmt, va_list args)
+{
+ struct trace_seq *s = this_cpu_ptr(&nmi_print_seq);
+ int len = s->len;
+
+ trace_seq_vprintf(s, fmt, args);
+ return s->len - len;
}
static int
@@ -68,12 +124,14 @@ arch_trigger_all_cpu_backtrace_handler(unsigned int cmd, struct pt_regs *regs)
cpu = smp_processor_id();
if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
- static arch_spinlock_t lock = __ARCH_SPIN_LOCK_UNLOCKED;
+ printk_func_t printk_func_save = this_cpu_read(printk_func);
- arch_spin_lock(&lock);
- printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu);
+ /* Replace printk to write into the NMI seq */
+ this_cpu_write(printk_func, nmi_vprintk);
+ printk("NMI backtrace for cpu %d\n", cpu);
show_regs(regs);
- arch_spin_unlock(&lock);
+ this_cpu_write(printk_func, printk_func_save);
+
cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
return NMI_HANDLED;
}
--
2.0.0.rc2
next prev parent reply other threads:[~2014-06-19 21:39 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-19 21:33 [RFC][PATCH 0/3] x86/nmi: Print all cpu stacks from NMI safely Steven Rostedt
2014-06-19 21:33 ` [RFC][PATCH 1/3] trace_seq: Move the trace_seq code to lib/ Steven Rostedt
2014-06-20 4:45 ` Linus Torvalds
2014-06-20 16:21 ` Steven Rostedt
2014-06-20 5:06 ` Andrew Morton
2014-06-20 16:58 ` Steven Rostedt
2014-06-20 17:12 ` Andrew Morton
2014-06-20 17:17 ` Steven Rostedt
2014-06-20 20:28 ` Steven Rostedt
2014-06-20 20:51 ` Steven Rostedt
2014-06-23 16:33 ` Petr Mládek
2014-06-23 17:03 ` Steven Rostedt
2014-06-22 7:38 ` Johannes Berg
2014-06-23 16:08 ` Steven Rostedt
2014-06-23 17:38 ` Johannes Berg
2014-06-23 18:04 ` Steven Rostedt
2014-06-24 8:19 ` Johannes Berg
2014-06-19 21:33 ` [RFC][PATCH 2/3] printk: Add per_cpu printk func to allow printk to be diverted Steven Rostedt
2014-06-23 16:06 ` Paul E. McKenney
2014-06-19 21:33 ` Steven Rostedt [this message]
2014-06-20 13:58 ` [RFC][PATCH 3/3] x86/nmi: Perform a safe NMI stack trace on all CPUs Don Zickus
2014-06-20 14:21 ` Steven Rostedt
2014-06-20 14:55 ` Petr Mládek
2014-06-20 15:17 ` Steven Rostedt
2014-06-23 16:12 ` Paul E. McKenney
2014-06-19 21:56 ` [RFC][PATCH 0/3] x86/nmi: Print all cpu stacks from NMI safely Jiri Kosina
2014-06-19 22:58 ` Steven Rostedt
2014-06-19 23:03 ` Jiri Kosina
2014-06-19 23:19 ` Steven Rostedt
2014-06-19 23:27 ` Jiri Kosina
2014-06-19 23:36 ` Steven Rostedt
2014-06-19 23:38 ` Jiri Kosina
2014-06-20 14:35 ` Petr Mládek
2014-06-24 13:32 ` Konstantin Khlebnikov
2014-06-25 10:01 ` Jiri Kosina
2014-06-25 11:04 ` Konstantin Khlebnikov
2014-06-25 11:57 ` Petr Mládek
2014-06-25 12:21 ` Petr Mládek
2014-11-19 4:39 [RFC][PATCH 0/3] printk/seq-buf/NMI: Revisit of safe NMI printing with seq_buf code Steven Rostedt
2014-11-19 4:39 ` [RFC][PATCH 3/3] x86/nmi: Perform a safe NMI stack trace on all CPUs Steven Rostedt
2014-11-19 10:41 ` Borislav Petkov
2014-11-19 10:44 ` Jiri Kosina
2014-11-19 10:53 ` Borislav Petkov
2014-11-19 13:02 ` Petr Mladek
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