[PATCH v2 1/2] xfs: add debug sysfs attribute set

[Brian Foster]

Create a top-level debug directory for global debug sysfs attributes.
This directory is added and removed on XFS module initialization and
removal respectively for DEBUG mode kernels only. It typically resides
at /sys/fs/xfs/debug. It is located at the top level of the xfs sysfs
hierarchy as attributes might define global behavior or behavior that
must be configured before an xfs mount is available (e.g., log recovery
behavior).

Define the global debug kobject that represents the debug sysfs
directory and add generic attribute show/store helpers to support future
attributes. No debug attributes are exported as of yet.

Signed-off-by: Brian Foster <***@redhat.com>
---
fs/xfs/xfs_super.c | 23 +++++++++++++++++++++--
fs/xfs/xfs_sysfs.c | 43 +++++++++++++++++++++++++++++++++++++++++++
fs/xfs/xfs_sysfs.h | 1 +
3 files changed, 65 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index b194652..919a64c 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -47,6 +47,7 @@
#include "xfs_dinode.h"
#include "xfs_filestream.h"
#include "xfs_quota.h"
+#include "xfs_sysfs.h"

#include <linux/namei.h>
#include <linux/init.h>
@@ -61,7 +62,11 @@
static const struct super_operations xfs_super_operations;
static kmem_zone_t *xfs_ioend_zone;
mempool_t *xfs_ioend_pool;
-struct kset *xfs_kset;
+
+struct kset *xfs_kset; /* top-level xfs sysfs dir */
+#ifdef DEBUG
+static struct xfs_kobj xfs_dbg_kobj; /* global debug sysfs attrs */
+#endif

#define MNTOPT_LOGBUFS "logbufs" /* number of XFS log buffers */
#define MNTOPT_LOGBSIZE "logbsize" /* size of XFS log buffers */
@@ -1768,9 +1773,16 @@ init_xfs_fs(void)
goto out_sysctl_unregister;;
}

- error = xfs_qm_init();
+#ifdef DEBUG
+ xfs_dbg_kobj.kobject.kset = xfs_kset;
+ error = xfs_sysfs_init(&xfs_dbg_kobj, &xfs_dbg_ktype, NULL, "debug");
if (error)
goto out_kset_unregister;
+#endif
+
+ error = xfs_qm_init();
+ if (error)
+ goto out_remove_kobj;

error = register_filesystem(&xfs_fs_type);
if (error)
@@ -1779,7 +1791,11 @@ init_xfs_fs(void)

out_qm_exit:
xfs_qm_exit();
+ out_remove_kobj:
+#ifdef DEBUG
+ xfs_sysfs_del(&xfs_dbg_kobj);
out_kset_unregister:
+#endif
kset_unregister(xfs_kset);
out_sysctl_unregister:
xfs_sysctl_unregister();
@@ -1802,6 +1818,9 @@ exit_xfs_fs(void)
{
xfs_qm_exit();
unregister_filesystem(&xfs_fs_type);
+#ifdef DEBUG
+ xfs_sysfs_del(&xfs_dbg_kobj);
+#endif
kset_unregister(xfs_kset);
xfs_sysctl_unregister();
xfs_cleanup_procfs();
diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
index 9835139..32ddf0c 100644
--- a/fs/xfs/xfs_sysfs.c
+++ b/fs/xfs/xfs_sysfs.c
@@ -51,6 +51,49 @@ struct kobj_type xfs_mp_ktype = {
.release = xfs_sysfs_release,
};

+#ifdef DEBUG
+/* debug */
+
+static struct attribute *xfs_dbg_attrs[] = {
+ NULL,
+};
+
+STATIC ssize_t
+xfs_dbg_show(
+ struct kobject *kobject,
+ struct attribute *attr,
+ char *buf)
+{
+ struct xfs_sysfs_attr *xfs_attr = to_attr(attr);
+
+ return xfs_attr->show ? xfs_attr->show(buf, NULL) : 0;
+}
+
+STATIC ssize_t
+xfs_dbg_store(
+ struct kobject *kobject,
+ struct attribute *attr,
+ const char *buf,
+ size_t count)
+{
+ struct xfs_sysfs_attr *xfs_attr = to_attr(attr);
+
+ return xfs_attr->store ? xfs_attr->store(buf, count, NULL) : 0;
+}
+
+static struct sysfs_ops xfs_dbg_ops = {
+ .show = xfs_dbg_show,
+ .store = xfs_dbg_store,
+};
+
+struct kobj_type xfs_dbg_ktype = {
+ .release = xfs_sysfs_release,
+ .sysfs_ops = &xfs_dbg_ops,
+ .default_attrs = xfs_dbg_attrs,
+};
+
+#endif /* DEBUG */
+
/* xlog */

STATIC ssize_t
diff --git a/fs/xfs/xfs_sysfs.h b/fs/xfs/xfs_sysfs.h
index 54a2091..240eee3 100644
--- a/fs/xfs/xfs_sysfs.h
+++ b/fs/xfs/xfs_sysfs.h
@@ -20,6 +20,7 @@
#define __XFS_SYSFS_H__

extern struct kobj_type xfs_mp_ktype; /* xfs_mount */
+extern struct kobj_type xfs_dbg_ktype; /* debug */
extern struct kobj_type xfs_log_ktype; /* xlog */

static inline struct xfs_kobj *

[Brian Foster]

XFS log recovery has been discovered to have race conditions with
buffers when I/O errors occur. External tools are available to simulate
I/O errors to XFS, but this alone is not sufficient for testing log
recovery. XFS unconditionally resets the inactive region of the log
prior to log recovery to avoid confusion over processing any partially
written log records that might have been written before an unclean
shutdown. Therefore, unconditional write I/O failures at mount time are
caught by the reset sequence rather than log recovery and hinder the
ability to test the latter.

The device-mapper dm-flakey module uses an up/down timer to define a
cycle for when to fail I/Os. Create a pre log recovery delay tunable
that can be used to coordinate XFS log recovery with I/O errors
simulated by dm-flakey. This facilitates coordination in userspace that
allows the reset of stale log blocks to succeed and writes due to log
recovery to fail. For example, define a dm-flakey instance with an
uptime long enough to allow log reset to succeed and a log recovery
delay long enough to allow the dm-flakey uptime to expire.

The 'log_recovery_delay' sysfs tunable is exported under
/sys/fs/xfs/debug and is only enabled for kernels compiled in XFS debug
mode. The value is exported in units of seconds and allows for a delay
of up to 60 seconds. Note that this is for XFS debug and test
instrumentation purposes only and should not be used by applications. No
delay is enabled by default.

Signed-off-by: Brian Foster <***@redhat.com>
---
fs/xfs/xfs_globals.c | 4 ++++
fs/xfs/xfs_log_recover.c | 12 ++++++++++++
fs/xfs/xfs_sysctl.h | 5 +++++
fs/xfs/xfs_sysfs.c | 31 +++++++++++++++++++++++++++++++
4 files changed, 52 insertions(+)

diff --git a/fs/xfs/xfs_globals.c b/fs/xfs/xfs_globals.c
index 5399ef2..4d41b24 100644
--- a/fs/xfs/xfs_globals.c
+++ b/fs/xfs/xfs_globals.c
@@ -43,3 +43,7 @@ xfs_param_t xfs_params = {
.fstrm_timer = { 1, 30*100, 3600*100},
.eofb_timer = { 1, 300, 3600*24},
};
+
+struct xfs_globals xfs_globals = {
+ .log_recovery_delay = 0, /* no delay by default */
+};
diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
index 1fd5787..176c4b3 100644
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -4509,6 +4509,18 @@ xlog_recover(
return -EINVAL;
}

+ /*
+ * Delay log recovery if the debug hook is set. This is debug
+ * instrumention to coordinate simulation of I/O failures with
+ * log recovery.
+ */
+ if (xfs_globals.log_recovery_delay) {
+ xfs_notice(log->l_mp,
+ "Delaying log recovery for %d seconds.",
+ xfs_globals.log_recovery_delay);
+ msleep(xfs_globals.log_recovery_delay * 1000);
+ }
+
xfs_notice(log->l_mp, "Starting recovery (logdev: %s)",
log->l_mp->m_logname ? log->l_mp->m_logname
: "internal");
diff --git a/fs/xfs/xfs_sysctl.h b/fs/xfs/xfs_sysctl.h
index bd8e157..ffef453 100644
--- a/fs/xfs/xfs_sysctl.h
+++ b/fs/xfs/xfs_sysctl.h
@@ -92,6 +92,11 @@ enum {

extern xfs_param_t xfs_params;

+struct xfs_globals {
+ int log_recovery_delay; /* log recovery delay (secs) */
+};
+extern struct xfs_globals xfs_globals;
+
#ifdef CONFIG_SYSCTL
extern int xfs_sysctl_register(void);
extern void xfs_sysctl_unregister(void);
diff --git a/fs/xfs/xfs_sysfs.c b/fs/xfs/xfs_sysfs.c
index 32ddf0c..aa03670 100644
--- a/fs/xfs/xfs_sysfs.c
+++ b/fs/xfs/xfs_sysfs.c
@@ -54,7 +54,38 @@ struct kobj_type xfs_mp_ktype = {
#ifdef DEBUG
/* debug */

+STATIC ssize_t
+log_recovery_delay_store(
+ const char *buf,
+ size_t count,
+ void *data)
+{
+ int ret;
+ int val;
+
+ ret = kstrtoint(buf, 0, &val);
+ if (ret)
+ return ret;
+
+ if (val < 0 || val > 60)
+ return -EINVAL;
+
+ xfs_globals.log_recovery_delay = val;
+
+ return count;
+}
+
+STATIC ssize_t
+log_recovery_delay_show(
+ char *buf,
+ void *data)
+{
+ return snprintf(buf, PAGE_SIZE, "%d\n", xfs_globals.log_recovery_delay);
+}
+XFS_SYSFS_ATTR_RW(log_recovery_delay);
+
static struct attribute *xfs_dbg_attrs[] = {
+ ATTR_LIST(log_recovery_delay),
NULL,
};

[Dave Chinner]

Here's v2 of the log recovery delay instrumentation set. v1 is available
http://oss.sgi.com/archives/xfs/2014-08/msg00276.html
After a brief conversation with Dave, we thought it best to tie in this
functionality with DEBUG mode to express/ensure that these attributes
are for debugging/hacking purposes only. Everything else should be
equivalent to v1.
Brian
- Enable /sys/fs/xfs/debug for DEBUG mode kernels only.
v1: http://oss.sgi.com/archives/xfs/2014-08/msg00276.html
xfs: add debug sysfs attribute set
xfs: export log_recovery_delay to delay mount time log recovery

These look good. I'm sure that as we add more attributes there will
be opportunity for factoring/streamlining this code more, but right
now I don't think that is necessary.

Reviewed-by: Dave Chinner <***@redhat.com>