Re: [V6 PATCH 1/6] panic/x86: Fix re-entrance problem due to panic on NMI
From: Borislav Petkov
Date: Thu Dec 10 2015 - 10:41:44 EST
On Thu, Dec 10, 2015 at 10:46:26AM +0900, Hidehiro Kawai wrote:
> If panic on NMI happens just after panic() on the same CPU, panic()
> is recursively called. As the result, it stalls after failing to
> acquire panic_lock.
>
> To avoid this problem, don't call panic() in NMI context if
> we've already entered panic().
>
> V6:
> - Add a comment about panic_cpu
> - Replace the magic number -1 for panic_cpu with a macro
>
> V4:
> - Improve comments in io_check_error() and panic()
>
> V3:
> - Introduce nmi_panic() macro to reduce code duplication
> - In the case of panic on NMI, don't return from NMI handlers
> if another CPU already panicked
>
> V2:
> - Use atomic_cmpxchg() instead of current spin_trylock() to
> exclude concurrent accesses to the panic routines
> - Don't introduce no-lock version of panic()
>
> Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> ---
> arch/x86/kernel/nmi.c | 16 ++++++++++++----
> include/linux/kernel.h | 21 +++++++++++++++++++++
> kernel/panic.c | 15 ++++++++++++---
> kernel/watchdog.c | 2 +-
> 4 files changed, 46 insertions(+), 8 deletions(-)
Looks better.
Did some comments cleanup and nmi_panic() macro reformatting so that it
is more readable and ended up applying this:
---
From: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
Date: Thu, 10 Dec 2015 10:46:26 +0900
Subject: [PATCH] panic, x86: Fix re-entrance problem due to panic on NMI
If panic on NMI happens just after panic() on the same CPU, panic() is
recursively called. Kernel stalls, as a result, after failing to acquire
panic_lock.
To avoid this problem, don't call panic() in NMI context if we've
already entered panic().
For that, introduce nmi_panic() macro to reduce code duplication. In
the case of panic on NMI, don't return from NMI handlers if another CPU
already panicked.
Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@xxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Aaron Tomlin <atomlin@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Cc: David Hildenbrand <dahi@xxxxxxxxxxxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Gobinda Charan Maji <gobinda.cemk07@xxxxxxxxx>
Cc: HATAYAMA Daisuke <d.hatayama@xxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Javi Merino <javi.merino@xxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: kexec@xxxxxxxxxxxxxxxxxxx
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: lkml <linux-kernel@xxxxxxxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: Nicolas Iooss <nicolas.iooss_linux@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Seth Jennings <sjenning@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Link: 20151210014626.25437.13302.stgit@softrs">http://lkml.kernel.org/r/20151210014626.25437.13302.stgit@softrs
[ Cleanup comments, fixup formatting. ]
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
arch/x86/kernel/nmi.c | 16 ++++++++++++----
include/linux/kernel.h | 20 ++++++++++++++++++++
kernel/panic.c | 16 +++++++++++++---
kernel/watchdog.c | 2 +-
4 files changed, 46 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 697f90db0e37..292a24bd0553 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -231,7 +231,7 @@ pci_serr_error(unsigned char reason, struct pt_regs *regs)
#endif
if (panic_on_unrecovered_nmi)
- panic("NMI: Not continuing");
+ nmi_panic("NMI: Not continuing");
pr_emerg("Dazed and confused, but trying to continue\n");
@@ -255,8 +255,16 @@ io_check_error(unsigned char reason, struct pt_regs *regs)
reason, smp_processor_id());
show_regs(regs);
- if (panic_on_io_nmi)
- panic("NMI IOCK error: Not continuing");
+ if (panic_on_io_nmi) {
+ nmi_panic("NMI IOCK error: Not continuing");
+
+ /*
+ * If end up here, it means we have received an NMI while
+ * processing panic(). Simply return without delaying and
+ * re-enabling NMI.
+ */
+ return;
+ }
/* Re-enable the IOCK line, wait for a few seconds */
reason = (reason & NMI_REASON_CLEAR_MASK) | NMI_REASON_CLEAR_IOCHK;
@@ -297,7 +305,7 @@ unknown_nmi_error(unsigned char reason, struct pt_regs *regs)
pr_emerg("Do you have a strange power saving mode enabled?\n");
if (unknown_nmi_panic || panic_on_unrecovered_nmi)
- panic("NMI: Not continuing");
+ nmi_panic("NMI: Not continuing");
pr_emerg("Dazed and confused, but trying to continue\n");
}
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 350dfb08aee3..750cc5c7c999 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -446,6 +446,26 @@ extern int sysctl_panic_on_stackoverflow;
extern bool crash_kexec_post_notifiers;
/*
+ * panic_cpu is used for synchronizing panic() and crash_kexec() execution. It
+ * holds a CPU number which is executing panic() currently. A value of
+ * PANIC_CPU_INVALID means no CPU has entered panic() or crash_kexec().
+ */
+extern atomic_t panic_cpu;
+#define PANIC_CPU_INVALID -1
+
+/*
+ * A variant of panic() called from NMI context. We return if we've already
+ * panicked on this CPU.
+ */
+#define nmi_panic(fmt, ...) \
+do { \
+ int cpu = raw_smp_processor_id(); \
+ \
+ if (atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, cpu) != cpu) \
+ panic(fmt, ##__VA_ARGS__); \
+} while (0)
+
+/*
* Only to be used by arch init code. If the user over-wrote the default
* CONFIG_PANIC_TIMEOUT, honor it.
*/
diff --git a/kernel/panic.c b/kernel/panic.c
index 4b150bc0c6c1..3344524cf6ff 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -61,6 +61,8 @@ void __weak panic_smp_self_stop(void)
cpu_relax();
}
+atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID);
+
/**
* panic - halt the system
* @fmt: The text string to print
@@ -71,17 +73,17 @@ void __weak panic_smp_self_stop(void)
*/
void panic(const char *fmt, ...)
{
- static DEFINE_SPINLOCK(panic_lock);
static char buf[1024];
va_list args;
long i, i_next = 0;
int state = 0;
+ int old_cpu, this_cpu;
/*
* Disable local interrupts. This will prevent panic_smp_self_stop
* from deadlocking the first cpu that invokes the panic, since
* there is nothing to prevent an interrupt handler (that runs
- * after the panic_lock is acquired) from invoking panic again.
+ * after setting panic_cpu) from invoking panic() again.
*/
local_irq_disable();
@@ -94,8 +96,16 @@ void panic(const char *fmt, ...)
* multiple parallel invocations of panic, all other CPUs either
* stop themself or will wait until they are stopped by the 1st CPU
* with smp_send_stop().
+ *
+ * `old_cpu == PANIC_CPU_INVALID' means this is the 1st CPU which
+ * comes here, so go ahead.
+ * `old_cpu == this_cpu' means we came from nmi_panic() which sets
+ * panic_cpu to this CPU. In this case, this is also the 1st CPU.
*/
- if (!spin_trylock(&panic_lock))
+ this_cpu = raw_smp_processor_id();
+ old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
+
+ if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu)
panic_smp_self_stop();
console_verbose();
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 18f34cf75f74..b9be18fae154 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -351,7 +351,7 @@ static void watchdog_overflow_callback(struct perf_event *event,
trigger_allbutself_cpu_backtrace();
if (hardlockup_panic)
- panic("Hard LOCKUP");
+ nmi_panic("Hard LOCKUP");
__this_cpu_write(hard_watchdog_warn, true);
return;
--
2.3.5
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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