core: Add kernel message dumper to call on oopses and panics

The core functionality is implemented as per Linus suggestion from

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

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

[dwmw2: Fix log_end handling]
Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
Reviewed-by: Anders Grafstrom <anders.grafstrom@netinsight.net>
Reviewed-by: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

2 files changed, 122 insertions, 0 deletions

diff --git a/kernel/panic.c b/kernel/panic.c
index bcdef26e3332..8c43226a544d 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>
@@ -74,6 +75,7 @@ NORET_TYPE void panic(const char * fmt, ...)
         dump_stack();
 #endif
 
+        kmsg_dump(KMSG_DUMP_PANIC);
         /*
          * If we have crashed and we have a crash kernel loaded let it handle
          * everything else.
@@ -338,6 +340,7 @@ void oops_exit(void)
 {
         do_oops_enter_exit();
         print_oops_end_marker();
+        kmsg_dump(KMSG_DUMP_OOPS);
 }
 
 #ifdef WANT_WARN_ON_SLOWPATH
diff --git a/kernel/printk.c b/kernel/printk.c
index f38b07f78a4e..051d1f50648f 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -33,6 +33,7 @@
 #include <linux/bootmem.h>
 #include <linux/syscalls.h>
 #include <linux/kexec.h>
+#include <linux/kmsg_dump.h>
 
 #include <asm/uaccess.h>
 
@@ -1405,3 +1406,121 @@ bool printk_timed_ratelimit(unsigned long *caller_jiffies,
 }
 EXPORT_SYMBOL(printk_timed_ratelimit);
 #endif
+
+static DEFINE_SPINLOCK(dump_list_lock);
+static LIST_HEAD(dump_list);
+
+/**
+ * kmsg_dump_register - register a kernel log dumper.
+ * @dump: pointer to the kmsg_dumper 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 kmsg_dump_register(struct kmsg_dumper *dumper)
+{
+        unsigned long flags;
+        int err = -EBUSY;
+
+        /* The dump callback needs to be set */
+        if (!dumper->dump)
+                return -EINVAL;
+
+        spin_lock_irqsave(&dump_list_lock, flags);
+        /* Don't allow registering multiple times */
+        if (!dumper->registered) {
+                dumper->registered = 1;
+                list_add_tail(&dumper->list, &dump_list);
+                err = 0;
+        }
+        spin_unlock_irqrestore(&dump_list_lock, flags);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_register);
+
+/**
+ * kmsg_dump_unregister - unregister a kmsg dumper.
+ * @dump: pointer to the kmsg_dumper structure
+ *
+ * Removes a dump device from the system. Returns zero on success and
+ * %-EINVAL otherwise.
+ */
+int kmsg_dump_unregister(struct kmsg_dumper *dumper)
+{
+        unsigned long flags;
+        int err = -EINVAL;
+
+        spin_lock_irqsave(&dump_list_lock, flags);
+        if (dumper->registered) {
+                dumper->registered = 0;
+                list_del(&dumper->list);
+                err = 0;
+        }
+        spin_unlock_irqrestore(&dump_list_lock, flags);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
+
+static const char const *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];
+}
+
+/**
+ * kmsg_dump - 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 kmsg_dump(enum kmsg_dump_reason reason)
+{
+        unsigned long end;
+        unsigned chars;
+        struct kmsg_dumper *dumper;
+        const char *s1, *s2;
+        unsigned long l1, l2;
+        unsigned long flags;
+
+        /* 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. */
+        spin_lock_irqsave(&logbuf_lock, flags);
+        end = log_end & LOG_BUF_MASK;
+        chars = logged_chars;
+        spin_unlock_irqrestore(&logbuf_lock, flags);
+
+        if (logged_chars > end) {
+                s1 = log_buf + log_buf_len - logged_chars + end;
+                l1 = logged_chars - end;
+
+                s2 = log_buf;
+                l2 = end;
+        } else {
+                s1 = "";
+                l1 = 0;
+
+                s2 = log_buf + end - logged_chars;
+                l2 = logged_chars;
+        }
+
+        if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
+                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_irqrestore(&dump_list_lock, flags);
+}