bcache: Add on error panic/unregister setting

Works kind of like the ext4 setting, to panic or remount read only on
errors.
Signed-off-by: Kent Overstreet <kmo@daterainc.com>

drivers/md/bcache/bcache.h

@@ -843,8 +843,14 @@ struct cache_set {
 	atomic_long_t		cache_read_races;
 	atomic_long_t		writeback_keys_done;
 	atomic_long_t		writeback_keys_failed;
+
+	enum			{
+		ON_ERROR_UNREGISTER,
+		ON_ERROR_PANIC,
+	}			on_error;
 	unsigned		error_limit;
 	unsigned		error_decay;
+
 	unsigned short		journal_delay_ms;
 	unsigned		verify:1;
 	unsigned		key_merging_disabled:1;

drivers/md/bcache/journal.c

@@ -305,10 +305,9 @@ int bch_journal_replay(struct cache_set *s, struct list_head *list,
 	list_for_each_entry(i, list, list) {
 		BUG_ON(i->pin && atomic_read(i->pin) != 1);
 
-		if (n != i->j.seq)
-			pr_err(
-		"journal entries %llu-%llu missing! (replaying %llu-%llu)\n",
-		n, i->j.seq - 1, start, end);
+		cache_set_err_on(n != i->j.seq, s,
+"bcache: journal entries %llu-%llu missing! (replaying %llu-%llu)",
+				 n, i->j.seq - 1, start, end);
 
 		for (k = i->j.start;
 		     k < end(&i->j);

drivers/md/bcache/super.c

@@ -1260,7 +1260,8 @@ bool bch_cache_set_error(struct cache_set *c, const char *fmt, ...)
 {
 	va_list args;
 
-	if (test_bit(CACHE_SET_STOPPING, &c->flags))
+	if (c->on_error != ON_ERROR_PANIC &&
+	    test_bit(CACHE_SET_STOPPING, &c->flags))
 		return false;
 
 	/* XXX: we can be called from atomic context
@@ -1275,6 +1276,9 @@ bool bch_cache_set_error(struct cache_set *c, const char *fmt, ...)
 
 	printk(", disabling caching\n");
 
+	if (c->on_error == ON_ERROR_PANIC)
+		panic("panic forced after error\n");
+
 	bch_cache_set_unregister(c);
 	return true;
 }

drivers/md/bcache/sysfs.c

@@ -21,6 +21,12 @@ static const char * const cache_replacement_policies[] = {
 	NULL
 };
 
+static const char * const error_actions[] = {
+	"unregister",
+	"panic",
+	NULL
+};
+
 write_attribute(attach);
 write_attribute(detach);
 write_attribute(unregister);
@@ -90,6 +96,7 @@ rw_attribute(discard);
 rw_attribute(running);
 rw_attribute(label);
 rw_attribute(readahead);
+rw_attribute(errors);
 rw_attribute(io_error_limit);
 rw_attribute(io_error_halflife);
 rw_attribute(verify);
@@ -492,6 +499,10 @@ SHOW(__bch_cache_set)
 	sysfs_print(writeback_keys_failed,
 		    atomic_long_read(&c->writeback_keys_failed));
 
+	if (attr == &sysfs_errors)
+		return bch_snprint_string_list(buf, PAGE_SIZE, error_actions,
+					       c->on_error);
+
 	/* See count_io_errors for why 88 */
 	sysfs_print(io_error_halflife,	c->error_decay * 88);
 	sysfs_print(io_error_limit,	c->error_limit >> IO_ERROR_SHIFT);
@@ -569,6 +580,15 @@ STORE(__bch_cache_set)
 	sysfs_strtoul(congested_write_threshold_us,
 		      c->congested_write_threshold_us);
 
+	if (attr == &sysfs_errors) {
+		ssize_t v = bch_read_string_list(buf, error_actions);
+
+		if (v < 0)
+			return v;
+
+		c->on_error = v;
+	}
+
 	if (attr == &sysfs_io_error_limit)
 		c->error_limit = strtoul_or_return(buf) << IO_ERROR_SHIFT;
 
@@ -620,6 +640,7 @@ static struct attribute *bch_cache_set_files[] = {
 	&sysfs_average_key_size,
 	&sysfs_dirty_data,
 
+	&sysfs_errors,
 	&sysfs_io_error_limit,
 	&sysfs_io_error_halflife,
 	&sysfs_congested,