Patchwork [v6,4/5] : core: Add kernel message dumper to call on oopses and panics

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Submitter Simon Kagstrom
Date Oct. 14, 2009, 1:41 p.m.
Message ID <20091014154118.5c8cc998@marrow.netinsight.se>
Download mbox | patch
Permalink /patch/35967/
State New
Headers show

Comments

Simon Kagstrom - Oct. 14, 2009, 1:41 p.m.
The core functionality is implemented as per Linus suggestion from

  http://lists.infradead.org/pipermail/linux-mtd/2009-October/027620.html

(with the dump_kmsg implementation by Linus). A struct kmsg_dumper has
been added which contains a callback to dump the kernel log buffers on
crashes. The dump_kmsg function gets called from oops_exit() and panic()
and invokes this callbacks with the crash reason.

Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
Reviewed-by: Anders Grafstrom <anders.grafstrom@netinsight.net>
---
ChangeLog:
Review comments from Linus Torvalds and Anders Grafström:
       * Rename structures and file names
       * Remove setup callback and unify panic/oops callbacks and
         instead add a reason parameter
       * Use a regular spinlock and try it when dumping (fail
         if held)
       * Check if the dumper is already registered
       * Various style fixes/cleanup

 include/linux/kmsg_dump.h |   37 ++++++++++++++++
 kernel/panic.c            |    3 +
 kernel/printk.c           |  105 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 145 insertions(+), 0 deletions(-)
 create mode 100644 include/linux/kmsg_dump.h
Linus Torvalds - Oct. 14, 2009, 4:49 p.m.
On Wed, 14 Oct 2009, Simon Kagstrom wrote:
>
> ChangeLog:
> Review comments from Linus Torvalds and Anders Grafström:
>        * Rename structures and file names
>        * Remove setup callback and unify panic/oops callbacks and
>          instead add a reason parameter
>        * Use a regular spinlock and try it when dumping (fail
>          if held)
>        * Check if the dumper is already registered
>        * Various style fixes/cleanup

Ok, looks fine to me now. 

I do end up having one minor nit: let's change the calling convention of 
the dump function to either be:

	void (*dump)(void *priv, enum kmsg_dump_reason reason,
		const char *s1, unsigned long l1,
		const char *s2, unsigned long l2);

or let's just remove the 'priv' data from the dump entirely. 

Right now, you pass in the whole 'kmsg_dumper' data structure, and then 
you seem to expect that users look up their private context by looking 
into that data structure with 'dumper->priv'. That's just ugly. 

So if you want to have a callback value, just pass that in for the 
callback.

And if you want to pass in the whole 'kmsg_dumper' data structure, then 
use that pointer _itself_ as the context (ie you would embed the 
'kmsg_dumper' in some data structure, and then you do

	struct my_data *my_data = container_of(dumper, struct my_data, dumper);

or something like that.

But your current implementation mixes _both_ of the above approaches. 
Which one are people going to use? Both work, and no, "there are multiple 
ways to do the same thing" is not an advantage, it just leads to 
confusion. And confusion isn't good, whatever the perl people say.

		Linus

Patch

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
new file mode 100644
index 0000000..a0d6b55
--- /dev/null
+++ b/include/linux/kmsg_dump.h
@@ -0,0 +1,37 @@ 
+/*
+ * linux/include/kmsg_dump.h
+ *
+ * Copyright (C) 2009 Net Insight AB
+ *
+ * Author: Simon Kagstrom <simon.kagstrom@netinsight.net>
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+#ifndef _LINUX_KMSG_DUMP_H
+#define _LINUX_KMSG_DUMP_H
+
+#include <linux/list.h>
+
+enum kmsg_dump_reason {
+	kmsg_dump_oops,
+	kmsg_dump_panic,
+};
+
+struct kmsg_dumper {
+	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason,
+			const char *s1, unsigned long l1,
+			const char *s2, unsigned long l2);
+	void *priv;
+	struct list_head list;
+	int registered;
+};
+
+void dump_kmsg(enum kmsg_dump_reason reason);
+
+int register_kmsg_dumper(struct kmsg_dumper *dumper, void *priv);
+
+void unregister_kmsg_dumper(struct kmsg_dumper *dumper);
+
+#endif /* _LINUX_DUMP_DEVICE_H */
diff --git a/kernel/panic.c b/kernel/panic.c
index c0b33b8..3a5a93f 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -10,6 +10,7 @@ 
  */
 #include <linux/debug_locks.h>
 #include <linux/interrupt.h>
+#include <linux/kmsg_dump.h>
 #include <linux/kallsyms.h>
 #include <linux/notifier.h>
 #include <linux/module.h>
@@ -76,6 +77,7 @@  NORET_TYPE void panic(const char * fmt, ...)
 	dump_stack();
 #endif
 
+	dump_kmsg(kmsg_dump_panic);
 	/*
 	 * If we have crashed and we have a crash kernel loaded let it handle
 	 * everything else.
@@ -341,6 +343,7 @@  void oops_exit(void)
 {
 	do_oops_enter_exit();
 	print_oops_end_marker();
+	dump_kmsg(kmsg_dump_oops);
 }
 
 #ifdef WANT_WARN_ON_SLOWPATH
diff --git a/kernel/printk.c b/kernel/printk.c
index f38b07f..a97abb0 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -33,6 +33,8 @@ 
 #include <linux/bootmem.h>
 #include <linux/syscalls.h>
 #include <linux/kexec.h>
+#include <linux/kmsg_dump.h>
+#include <linux/spinlock.h>
 
 #include <asm/uaccess.h>
 
@@ -1405,3 +1407,106 @@  bool printk_timed_ratelimit(unsigned long *caller_jiffies,
 }
 EXPORT_SYMBOL(printk_timed_ratelimit);
 #endif
+
+static LIST_HEAD(dump_list);
+static DEFINE_SPINLOCK(dump_list_lock);
+
+/**
+ *	register_dump_device - register a kernel log dumper.
+ *	@dump: pointer to the dump structure
+ *	@priv: private data for the structure
+ *
+ *	Adds a kernel log dumper to the system. The dump callback in the
+ *	structure will be called when the kernel oopses or panics and must be
+ *	set. Returns zero on success and -EINVAL or -EBUSY otherwise.
+ */
+int register_kmsg_dumper(struct kmsg_dumper *dumper, void *priv)
+{
+	unsigned long flags;
+
+	/* The dump callback needs to be set */
+	if (!dumper->dump)
+		return -EINVAL;
+
+	/* Don't allow registering multiple times */
+	if (dumper->registered)
+		return -EBUSY;
+
+	dumper->priv = priv;
+	dumper->registered = 1;
+
+	spin_lock_irqsave(&dump_list_lock, flags);
+	list_add(&dumper->list, &dump_list);
+	spin_unlock_irqrestore(&dump_list_lock, flags);
+	return 0;
+}
+EXPORT_SYMBOL(register_kmsg_dumper);
+
+/**
+ *	unregister_dump_device - unregister a dumpdevice.
+ *	@dump: pointer to the dump structure
+ *
+ *	Removes a dump device from the system.
+ */
+void unregister_kmsg_dumper(struct kmsg_dumper *dumper)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&dump_list_lock, flags);
+	list_del(&dumper->list);
+	spin_unlock_irqrestore(&dump_list_lock, flags);
+}
+EXPORT_SYMBOL(unregister_kmsg_dumper);
+
+static const char *kmsg_reasons[] = {
+	[kmsg_dump_oops]	= "oops",
+	[kmsg_dump_panic]	= "panic",
+};
+
+static const char *kmsg_to_str(enum kmsg_dump_reason reason)
+{
+	if (reason > ARRAY_SIZE(kmsg_reasons) || reason < 0)
+		return "unknown";
+
+	return kmsg_reasons[reason];
+}
+
+/**
+ *	dump_kmsg - dump kernel log to kernel message dumpers.
+ *	@reason: the reason (oops, panic etc) for dumping
+ *
+ *	Iterate through each of the dump devices and call the oops/panic
+ *	callbacks with the log buffer.
+ */
+void dump_kmsg(enum kmsg_dump_reason reason)
+{
+	unsigned long len = ACCESS_ONCE(log_end);
+	struct kmsg_dumper *dumper;
+	const char *s1, *s2;
+	unsigned long l1, l2;
+
+	s1 = "";
+	l1 = 0;
+	s2 = log_buf;
+	l2 = len;
+
+	/* Have we rotated around the circular buffer? */
+	if (len > log_buf_len) {
+		unsigned long pos = len & LOG_BUF_MASK;
+
+		s1 = log_buf + pos;
+		l1 = log_buf_len - pos;
+
+		s2 = log_buf;
+		l2 = pos;
+	}
+
+	if (!spin_trylock(&dump_list_lock)) {
+		printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
+				kmsg_to_str(reason));
+		return;
+	}
+	list_for_each_entry(dumper, &dump_list, list)
+		dumper->dump(dumper, reason, s1, l1, s2, l2);
+	spin_unlock(&dump_list_lock);
+}