[PATCH 1/2] ext4: add debugging trigger for ext4_error()

[PATCH 1/2] ext4: add debugging trigger for ext4_error()

[Theodore Ts'o]

Make it easy to test whether or not the error handling subsystem in
ext4 is working correctly.  This allows us to simulate an ext4_error()
by echoing a string to /sys/fs/ext4/<dev>/trigger_fs_error.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: ksumrall@google.com
---
 fs/ext4/ext4.h  |  1 +
 fs/ext4/super.c | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 511011a..decc15d 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1197,6 +1197,7 @@ struct ext4_sb_info {
 	struct proc_dir_entry *s_proc;
 	struct kobject s_kobj;
 	struct completion s_kobj_unregister;
+	struct super_block *s_sb;
 
 	/* Journaling */
 	struct journal_s *s_journal;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 628cfcd..9f1ae6b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2473,6 +2473,23 @@ static ssize_t sbi_ui_store(struct ext4_attr *a,
 	return count;
 }
 
+static ssize_t trigger_test_error(struct ext4_attr *a,
+				  struct ext4_sb_info *sbi,
+				  const char *buf, size_t count)
+{
+	int len = count;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (len && buf[len-1] == '\n')
+		len--;
+
+	if (len)
+		ext4_error(sbi->s_sb, "%.*s", len, buf);
+	return count;
+}
+
 #define EXT4_ATTR_OFFSET(_name,_mode,_show,_store,_elname) \
 static struct ext4_attr ext4_attr_##_name = {			\
 	.attr = {.name = __stringify(_name), .mode = _mode },	\
@@ -2503,6 +2520,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
 EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
 EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
 EXT4_RW_ATTR_SBI_UI(max_writeback_mb_bump, s_max_writeback_mb_bump);
+EXT4_ATTR(trigger_fs_error, 0200, NULL, trigger_test_error);
 
 static struct attribute *ext4_attrs[] = {
 	ATTR_LIST(delayed_allocation_blocks),
@@ -2517,6 +2535,7 @@ static struct attribute *ext4_attrs[] = {
 	ATTR_LIST(mb_stream_req),
 	ATTR_LIST(mb_group_prealloc),
 	ATTR_LIST(max_writeback_mb_bump),
+	ATTR_LIST(trigger_fs_error),
 	NULL,
 };
 
@@ -3087,6 +3106,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		goto out_free_orig;
 	}
 	sb->s_fs_info = sbi;
+	sbi->s_sb = sb;
 	sbi->s_mount_opt = 0;
 	sbi->s_resuid = EXT4_DEF_RESUID;
 	sbi->s_resgid = EXT4_DEF_RESGID;
-- 
1.7.10.2.552.gaa3bb87

[PATCH 2/2] ext4: add missing save_error_info() to ext4_error()

[Theodore Ts'o]

The ext4_error() function is missing a call to save_error_info().
Since this is the function which marks the file system as containing
an error, this oversight (which was introduced in 2.6.36) is quite
significant, and should be backported to older stable kernels with
high urgency.

Reported-by: Ken Sumrall <ksumrall@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: ksumrall@google.com
Cc: stable@kernel.org
---
 fs/ext4/super.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 9f1ae6b..b8d5fc1 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -539,6 +539,7 @@ void __ext4_error(struct super_block *sb, const char *function,
 	printk(KERN_CRIT "EXT4-fs error (device %s): %s:%d: comm %s: %pV\n",
 	       sb->s_id, function, line, current->comm, &vaf);
 	va_end(args);
+	save_error_info(sb, function, line);
 
 	ext4_handle_error(sb);
 }
-- 
1.7.10.2.552.gaa3bb87