printk: Add a short description string to kmsg_dump()

kmsg_dump doesn't forward the panic reason string to the kmsg_dumper
callback.
This patch adds a new struct kmsg_dump_detail, that will hold the
reason and description, and pass it to the dump() callback.

To avoid updating all kmsg_dump() call, it adds a kmsg_dump_desc()
function and a macro for backward compatibility.

I've written this for drm_panic, but it can be useful for other
kmsg_dumper.
It allows to see the panic reason, like "sysrq triggered crash"
or "VFS: Unable to mount root fs on xxxx" on the drm panic screen.

v2:
 * Use a struct kmsg_dump_detail to hold the reason and description
   pointer, for more flexibility if we want to add other parameters.
   (Kees Cook)
 * Fix powerpc/nvram_64 build, as I didn't update the forward
   declaration of oops_to_nvram()

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Acked-by: Petr Mladek <pmladek@suse.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Acked-by: Kees Cook <kees@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240702122639.248110-1-jfalempe@redhat.com

arch/powerpc/kernel/nvram_64.c

@@ -73,7 +73,7 @@ static const char *nvram_os_partitions[] = {
 };
 
 static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason);
+			  struct kmsg_dump_detail *detail);
 
 static struct kmsg_dumper nvram_kmsg_dumper = {
 	.dump = oops_to_nvram
@@ -643,7 +643,7 @@ void __init nvram_init_oops_partition(int rtas_partition_exists)
  * partition.  If that's too much, go back and capture uncompressed text.
  */
 static void oops_to_nvram(struct kmsg_dumper *dumper,
-			  enum kmsg_dump_reason reason)
+			  struct kmsg_dump_detail *detail)
 {
 	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
 	static unsigned int oops_count = 0;
@@ -655,7 +655,7 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 	unsigned int err_type = ERR_TYPE_KERNEL_PANIC_GZ;
 	int rc = -1;
 
-	switch (reason) {
+	switch (detail->reason) {
 	case KMSG_DUMP_SHUTDOWN:
 		/* These are almost always orderly shutdowns. */
 		return;
@@ -671,7 +671,7 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 		break;
 	default:
 		pr_err("%s: ignoring unrecognized KMSG_DUMP_* reason %d\n",
-		       __func__, (int) reason);
+		       __func__, (int) detail->reason);
 		return;
 	}
 

arch/powerpc/platforms/powernv/opal-kmsg.c

@@ -20,13 +20,13 @@
  * message, it just ensures that OPAL completely flushes the console buffer.
  */
 static void kmsg_dump_opal_console_flush(struct kmsg_dumper *dumper,
-				     enum kmsg_dump_reason reason)
+				     struct kmsg_dump_detail *detail)
 {
 	/*
 	 * Outside of a panic context the pollers will continue to run,
 	 * so we don't need to do any special flushing.
 	 */
-	if (reason != KMSG_DUMP_PANIC)
+	if (detail->reason != KMSG_DUMP_PANIC)
 		return;
 
 	opal_flush_console(0);

arch/um/kernel/kmsg_dump.c

@@ -8,7 +8,7 @@
 #include <os.h>
 
 static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
-				enum kmsg_dump_reason reason)
+				struct kmsg_dump_detail *detail)
 {
 	static struct kmsg_dump_iter iter;
 	static DEFINE_SPINLOCK(lock);

drivers/gpu/drm/drm_panic.c

@@ -655,11 +655,11 @@ static struct drm_plane *to_drm_plane(struct kmsg_dumper *kd)
 	return container_of(kd, struct drm_plane, kmsg_panic);
 }
 
-static void drm_panic(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason)
+static void drm_panic(struct kmsg_dumper *dumper, struct kmsg_dump_detail *detail)
 {
 	struct drm_plane *plane = to_drm_plane(dumper);
 
-	if (reason == KMSG_DUMP_PANIC)
+	if (detail->reason == KMSG_DUMP_PANIC)
 		draw_panic_plane(plane);
 }
 

drivers/hv/hv_common.c

@@ -207,13 +207,13 @@ static int hv_die_panic_notify_crash(struct notifier_block *self,
  * buffer and call into Hyper-V to transfer the data.
  */
 static void hv_kmsg_dump(struct kmsg_dumper *dumper,
-			 enum kmsg_dump_reason reason)
+			 struct kmsg_dump_detail *detail)
 {
 	struct kmsg_dump_iter iter;
 	size_t bytes_written;
 
 	/* We are only interested in panics. */
-	if (reason != KMSG_DUMP_PANIC || !sysctl_record_panic_msg)
+	if (detail->reason != KMSG_DUMP_PANIC || !sysctl_record_panic_msg)
 		return;
 
 	/*

drivers/mtd/mtdoops.c

@@ -298,7 +298,7 @@ static void find_next_position(struct mtdoops_context *cxt)
 }
 
 static void mtdoops_do_dump(struct kmsg_dumper *dumper,
-			    enum kmsg_dump_reason reason)
+			    struct kmsg_dump_detail *detail)
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);

fs/pstore/platform.c

@@ -275,7 +275,7 @@ void pstore_record_init(struct pstore_record *record,
  * end of the buffer.
  */
 static void pstore_dump(struct kmsg_dumper *dumper,
-			enum kmsg_dump_reason reason)
+			struct kmsg_dump_detail *detail)
 {
 	struct kmsg_dump_iter iter;
 	unsigned long	total = 0;
@@ -285,9 +285,9 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 	int		saved_ret = 0;
 	int		ret;
 
-	why = kmsg_dump_reason_str(reason);
+	why = kmsg_dump_reason_str(detail->reason);
 
-	if (pstore_cannot_block_path(reason)) {
+	if (pstore_cannot_block_path(detail->reason)) {
 		if (!spin_trylock_irqsave(&psinfo->buf_lock, flags)) {
 			pr_err("dump skipped in %s path because of concurrent dump\n",
 					in_nmi() ? "NMI" : why);
@@ -311,7 +311,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		pstore_record_init(&record, psinfo);
 		record.type = PSTORE_TYPE_DMESG;
 		record.count = oopscount;
-		record.reason = reason;
+		record.reason = detail->reason;
 		record.part = part;
 		record.buf = psinfo->buf;
 
@@ -352,7 +352,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		}
 
 		ret = psinfo->write(&record);
-		if (ret == 0 && reason == KMSG_DUMP_OOPS) {
+		if (ret == 0 && detail->reason == KMSG_DUMP_OOPS) {
 			pstore_new_entry = 1;
 			pstore_timer_kick();
 		} else {

include/linux/kmsg_dump.h

@@ -39,6 +39,17 @@ struct kmsg_dump_iter {
 	u64	next_seq;
 };
 
+/**
+ * struct kmsg_dump_detail - kernel crash detail
+ * @reason: reason for the crash, see kmsg_dump_reason.
+ * @description: optional short string, to provide additional information.
+ */
+
+struct kmsg_dump_detail {
+	enum kmsg_dump_reason reason;
+	const char *description;
+};
+
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
@@ -49,13 +60,13 @@ struct kmsg_dump_iter {
  */
 struct kmsg_dumper {
 	struct list_head list;
-	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
+	void (*dump)(struct kmsg_dumper *dumper, struct kmsg_dump_detail *detail);
 	enum kmsg_dump_reason max_reason;
 	bool registered;
 };
 
 #ifdef CONFIG_PRINTK
-void kmsg_dump(enum kmsg_dump_reason reason);
+void kmsg_dump_desc(enum kmsg_dump_reason reason, const char *desc);
 
 bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
@@ -71,7 +82,7 @@ int kmsg_dump_unregister(struct kmsg_dumper *dumper);
 
 const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason);
 #else
-static inline void kmsg_dump(enum kmsg_dump_reason reason)
+static inline void kmsg_dump_desc(enum kmsg_dump_reason reason, const char *desc)
 {
 }
 
@@ -107,4 +118,9 @@ static inline const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
 }
 #endif
 
+static inline void kmsg_dump(enum kmsg_dump_reason reason)
+{
+	kmsg_dump_desc(reason, NULL);
+}
+
 #endif /* _LINUX_KMSG_DUMP_H */

kernel/panic.c

@@ -375,7 +375,7 @@ void panic(const char *fmt, ...)
 
 	panic_print_sys_info(false);
 
-	kmsg_dump(KMSG_DUMP_PANIC);
+	kmsg_dump_desc(KMSG_DUMP_PANIC, buf);
 
 	/*
 	 * If you doubt kdump always works fine in any situation,

kernel/printk/printk.c

@@ -4126,16 +4126,21 @@ const char *kmsg_dump_reason_str(enum kmsg_dump_reason reason)
 EXPORT_SYMBOL_GPL(kmsg_dump_reason_str);
 
 /**
- * kmsg_dump - dump kernel log to kernel message dumpers.
+ * kmsg_dump_desc - dump kernel log to kernel message dumpers.
  * @reason: the reason (oops, panic etc) for dumping
+ * @desc: a short string to describe what caused the panic or oops. Can be NULL
+ * if no additional description is available.
  *
  * Call each of the registered dumper's dump() callback, which can
  * retrieve the kmsg records with kmsg_dump_get_line() or
  * kmsg_dump_get_buffer().
  */
-void kmsg_dump(enum kmsg_dump_reason reason)
+void kmsg_dump_desc(enum kmsg_dump_reason reason, const char *desc)
 {
 	struct kmsg_dumper *dumper;
+	struct kmsg_dump_detail detail = {
+		.reason = reason,
+		.description = desc};
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list) {
@@ -4153,7 +4158,7 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 			continue;
 
 		/* invoke dumper which will iterate over records */
-		dumper->dump(dumper, reason);
+		dumper->dump(dumper, &detail);
 	}
 	rcu_read_unlock();
 }