linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
To: Jonathan Corbet <corbet@lwn.net>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vivek Goyal <vgoyal@redhat.com>
Cc: linux-doc@vger.kernel.org, x86@kernel.org,
	kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
	Michal Hocko <mhocko@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Subject: [V4 PATCH 2/4] panic/x86: Allow cpus to save registers even if they are looping in NMI context
Date: Fri, 25 Sep 2015 20:28:07 +0900	[thread overview]
Message-ID: <20150925112807.4258.12180.stgit@softrs> (raw)
In-Reply-To: <20150925112803.4258.94241.stgit@softrs>

nmi_shootdown_cpus(), a subroutine of crash_kexec(), sends NMI IPI
to non-panic cpus to stop them while saving their register
information and doing some cleanups for crash dumping.  So if a
non-panic cpus is infinitely looping in NMI context, we fail to
save its register information and lose the information from the
crash dump.

`Infinite loop in NMI context' can happen when panic on NMI happens
while another cpu has already been processing panic().  To save
registers in that case too, this patch does following two things:

1. Move the timing of `infinite loop in NMI context' (actually
   done by panic_smp_self_stop()) outside of panic() to enable us to
   refer pt_regs
2. call a callback of nmi_shootdown_cpus() directly to save
   registers and do some cleanups after setting waiting_for_crash_ipi
   which is used for counting down the number of cpus which handled
   the callback

V4:
- Rewrite the patch description

V3:
- Newly introduced

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
---
 arch/x86/kernel/nmi.c    |    6 +++---
 arch/x86/kernel/reboot.c |   11 +++++++++++
 include/linux/kernel.h   |   12 ++++++++++--
 kernel/panic.c           |   10 ++++++++++
 kernel/watchdog.c        |    5 +++--
 5 files changed, 37 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/nmi.c b/arch/x86/kernel/nmi.c
index 5131714..5e00de7 100644
--- a/arch/x86/kernel/nmi.c
+++ b/arch/x86/kernel/nmi.c
@@ -231,7 +231,7 @@ void unregister_nmi_handler(unsigned int type, const char *name)
 #endif
 
 	if (panic_on_unrecovered_nmi)
-		nmi_panic("NMI: Not continuing");
+		nmi_panic(regs, "NMI: Not continuing");
 
 	pr_emerg("Dazed and confused, but trying to continue\n");
 
@@ -256,7 +256,7 @@ void unregister_nmi_handler(unsigned int type, const char *name)
 	show_regs(regs);
 
 	if (panic_on_io_nmi) {
-		nmi_panic("NMI IOCK error: Not continuing");
+		nmi_panic(regs, "NMI IOCK error: Not continuing");
 
 		/*
 		 * If we return from nmi_panic(), it means we have received
@@ -305,7 +305,7 @@ void unregister_nmi_handler(unsigned int type, const char *name)
 
 	pr_emerg("Do you have a strange power saving mode enabled?\n");
 	if (unknown_nmi_panic || panic_on_unrecovered_nmi)
-		nmi_panic("NMI: Not continuing");
+		nmi_panic(regs, "NMI: Not continuing");
 
 	pr_emerg("Dazed and confused, but trying to continue\n");
 }
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 02693dd..d82259b 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -718,6 +718,7 @@ void machine_crash_shutdown(struct pt_regs *regs)
 static nmi_shootdown_cb shootdown_callback;
 
 static atomic_t waiting_for_crash_ipi;
+static int crash_ipi_done;
 
 static int crash_nmi_callback(unsigned int val, struct pt_regs *regs)
 {
@@ -779,6 +780,7 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 	wmb();
 
 	smp_send_nmi_allbutself();
+	crash_ipi_done = 1; /* Kick cpus looping in nmi context */
 
 	msecs = 1000; /* Wait at most a second for the other cpus to stop */
 	while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
@@ -788,6 +790,15 @@ void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 
 	/* Leave the nmi callback set */
 }
+
+void nmi_panic_self_stop(struct pt_regs *regs)
+{
+	while (crash_ipi_done == 0)
+		cpu_relax();
+
+	crash_nmi_callback(0, regs); /* Shouldn't return */
+}
+
 #else /* !CONFIG_SMP */
 void nmi_shootdown_cpus(nmi_shootdown_cb callback)
 {
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 57c33da..9fe9961 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -255,6 +255,7 @@ static inline void might_fault(void) { }
 __printf(1, 2)
 void panic(const char *fmt, ...)
 	__noreturn __cold;
+void nmi_panic_self_stop(struct pt_regs *);
 extern void oops_enter(void);
 extern void oops_exit(void);
 void print_oops_end_marker(void);
@@ -448,12 +449,19 @@ extern __scanf(2, 0)
 /*
  * A variant of panic() called from NMI context.
  * If we've already panicked on this cpu, return from here.
+ * If another cpu already panicked, loop in nmi_panic_self_stop() which
+ * can provide architecture dependent code such as saving register states
+ * for crash dump.
  */
-#define nmi_panic(fmt, ...)						\
+#define nmi_panic(regs, fmt, ...)					\
 	do {								\
+		int old_cpu;						\
 		int this_cpu = raw_smp_processor_id();			\
-		if (atomic_cmpxchg(&panic_cpu, -1, this_cpu) != this_cpu) \
+		old_cpu = atomic_cmpxchg(&panic_cpu, -1, this_cpu);	\
+		if (old_cpu == -1)					\
 			panic(fmt, ##__VA_ARGS__);			\
+		else if (old_cpu != this_cpu)				\
+			nmi_panic_self_stop(regs);			\
 	} while (0)
 
 /*
diff --git a/kernel/panic.c b/kernel/panic.c
index a105e67..cddbfe0 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -60,6 +60,16 @@ void __weak panic_smp_self_stop(void)
 		cpu_relax();
 }
 
+/*
+ * Stop ourself in NMI context if another cpu has already panicked.
+ * Architecture code may override this to prepare for crash dumping
+ * (e.g. save register information).
+ */
+void __weak nmi_panic_self_stop(struct pt_regs *regs)
+{
+	panic_smp_self_stop();
+}
+
 atomic_t panic_cpu = ATOMIC_INIT(-1);
 
 /**
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 00fbaa29..0074e5d 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -324,8 +324,9 @@ static void watchdog_overflow_callback(struct perf_event *event,
 			return;
 
 		if (hardlockup_panic)
-			nmi_panic("Watchdog detected hard LOCKUP on cpu %d",
-			      this_cpu);
+			nmi_panic(regs,
+				  "Watchdog detected hard LOCKUP on cpu %d",
+				  this_cpu);
 		else
 			WARN(1, "Watchdog detected hard LOCKUP on cpu %d",
 			     this_cpu);



  parent reply	other threads:[~2015-09-25 12:03 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-25 11:28 [V4 PATCH 0/4] Fix race issues among panic, NMI and crash_kexec Hidehiro Kawai
2015-09-25 11:28 ` [V4 PATCH 1/4] panic/x86: Fix re-entrance problem due to panic on NMI Hidehiro Kawai
2015-09-25 12:13   ` 河合英宏 / KAWAI,HIDEHIRO
2015-09-30 11:26     ` Peter Zijlstra
2015-10-01  1:02       ` 河合英宏 / KAWAI,HIDEHIRO
2015-09-25 11:28 ` Hidehiro Kawai [this message]
2015-09-30 11:50   ` [V4 PATCH 2/4] panic/x86: Allow cpus to save registers even if they are looping in NMI context Peter Zijlstra
2015-10-01  1:43     ` 河合英宏 / KAWAI,HIDEHIRO
2015-09-25 11:28 ` [V4 PATCH 3/4] kexec: Fix race between panic() and crash_kexec() called directly Hidehiro Kawai
2015-09-28  3:53   ` kbuild test robot
2015-09-28  7:08     ` 河合英宏 / KAWAI,HIDEHIRO
2015-09-30 11:53       ` Peter Zijlstra
2015-10-01  2:04         ` 河合英宏 / KAWAI,HIDEHIRO
2015-09-28  4:02   ` kbuild test robot
2015-09-28  4:46     ` 河合英宏 / KAWAI,HIDEHIRO
2015-09-25 11:28 ` [V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option Hidehiro Kawai
2015-09-30 11:55   ` Peter Zijlstra
2015-10-01  2:33     ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-01  6:27       ` Peter Zijlstra
2015-10-01  7:01         ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-01  8:43           ` Borislav Petkov
2015-10-01 10:24             ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-01 11:01               ` Borislav Petkov
2015-10-02  0:58                 ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-02  7:47                   ` Borislav Petkov
2015-10-05  2:03                     ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-05  8:27                       ` Borislav Petkov
2015-10-05  9:21                         ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-05 10:14                           ` Borislav Petkov
2015-10-13 11:55                             ` 河合英宏 / KAWAI,HIDEHIRO
     [not found]                         ` <alpine.DEB.2.11.1510132210590.25029@nanos>
2015-10-14 13:54                           ` Ingo Molnar
2015-10-16  1:58                             ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-13 20:22   ` Thomas Gleixner
2015-10-14  3:39     ` 河合英宏 / KAWAI,HIDEHIRO
     [not found]       ` <alpine.DEB.2.11.1510140924370.25029@nanos>
2015-10-16  2:02         ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-27  8:46   ` Baoquan He
2015-10-27  9:01     ` 河合英宏 / KAWAI,HIDEHIRO
2015-10-27  9:06       ` 'Baoquan He'

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20150925112807.4258.12180.stgit@softrs \
    --to=hidehiro.kawai.ez@hitachi.com \
    --cc=akpm@linux-foundation.org \
    --cc=corbet@lwn.net \
    --cc=ebiederm@xmission.com \
    --cc=hpa@zytor.com \
    --cc=kexec@lists.infradead.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=masami.hiramatsu.pt@hitachi.com \
    --cc=mhocko@kernel.org \
    --cc=mingo@kernel.org \
    --cc=mingo@redhat.com \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=vgoyal@redhat.com \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).