[RFC][PATCH -next] make pstore/kmsg_dump run after stopping othercpus in panic path

[Seiji Aguchi]

Hi,
 
 As Don mentioned in following thread, it would be nice for pstore/kmsg_dump to serialize 
 panic path and have one cpu running because they can log messages reliably. 
 
 https://lkml.org/lkml/2011/10/13/427
 
 For realizing this idea, we have to move kmsg_dump below smp_send_stop() and bust some locks 
 of kmsg_dump/pstore in panic path.

 This patch does followings.

  - moving kmsg_dump(KMSG_DUMP_PANIC) below smp_send_stop.
  - busting logbuf_lock of kmsg_dump() in panic path for avoiding deadlock.
  - busting psinfo->buf_lock of pstore_dump() in panic path for avoiding deadlock.

Any comments are welcome.

 Signed-off-by: Seiji Aguchi <seiji.aguchi@xxxxxxx>

---
 fs/pstore/platform.c |   22 ++++++++++------------
 kernel/panic.c       |    4 ++--
 kernel/printk.c      |    7 +++++++
 3 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index 2bd620f..e73d940 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -90,19 +90,21 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 	int		hsize, ret;
 	unsigned int	part = 1;
 	unsigned long	flags = 0;
-	int		is_locked = 0;
 
 	if (reason < ARRAY_SIZE(reason_str))
 		why = reason_str[reason];
 	else
 		why = "Unknown";
 
-	if (in_nmi()) {
-		is_locked = spin_trylock(&psinfo->buf_lock);
-		if (!is_locked)
-			pr_err("pstore dump routine blocked in NMI, may corrupt error record\n");
-	} else
-		spin_lock_irqsave(&psinfo->buf_lock, flags);
+	/*
+	 * pstore_dump() is called after smp_send_stop() in panic path.
+	 * So, spin_lock should be bust for avoiding deadlock.
+	 */
+	if (reason == KMSG_DUMP_PANIC)
+		spin_lock_init(&psinfo->buf_lock);
+
+	spin_lock_irqsave(&psinfo->buf_lock, flags);
+
 	oopscount++;
 	while (total < kmsg_bytes) {
 		dst = psinfo->buf;
@@ -131,11 +133,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		total += l1_cpy + l2_cpy;
 		part++;
 	}
-	if (in_nmi()) {
-		if (is_locked)
-			spin_unlock(&psinfo->buf_lock);
-	} else
-		spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+	spin_unlock_irqrestore(&psinfo->buf_lock, flags);
 }
 
 static struct kmsg_dumper pstore_dumper = {
diff --git a/kernel/panic.c b/kernel/panic.c
index d7bb697..41bf6ad 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -88,8 +88,6 @@ NORET_TYPE void panic(const char * fmt, ...)
 	 */
 	crash_kexec(NULL);
 
-	kmsg_dump(KMSG_DUMP_PANIC);
-
 	/*
 	 * Note smp_send_stop is the usual smp shutdown function, which
 	 * unfortunately means it may not be hardened to work in a panic
@@ -97,6 +95,8 @@ NORET_TYPE void panic(const char * fmt, ...)
 	 */
 	smp_send_stop();
 
+	kmsg_dump(KMSG_DUMP_PANIC);
+
 	atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
 
 	bust_spinlocks(0);
diff --git a/kernel/printk.c b/kernel/printk.c
index 1455a0d..e1e57db 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1732,6 +1732,13 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 	unsigned long l1, l2;
 	unsigned long flags;
 
+	/*
+	 *  kmsg_dump() is called after smp_send_stop() in panic path.
+	 *  So, spin_lock should be bust for avoiding deadlock.
+	 */
+	if (reason == KMSG_DUMP_PANIC)
+		raw_spin_lock_init(&logbuf_lock);
+
 	/* Theoretically, the log could move on after we do this, but
 	   there's not a lot we can do about that. The new messages
 	   will overwrite the start of what we dump. */
-- 
1.7.1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/