[PATCH v7 8/8] block: create the request_queue debugfs_dir on registration

Luis Chamberlain
2020-06-19T20:48:02Z

We were only creating the request_queue debugfs_dir only
for make_request block drivers (multiqueue), but never for
request-based block drivers. We did this as we were only
creating non-blktrace additional debugfs files on that directory
for make_request drivers. However, since blktrace *always* creates
that directory anyway, we special-case the use of that directory
on blktrace. Other than this being an eye-sore, this exposes
request-based block drivers to the same debugfs fragile
race that used to exist with make_request block drivers
where if we start adding files onto that directory we can later
run a race with a double removal of dentries on the directory
if we don't deal with this carefully on blktrace.

Instead, just simplify things by always creating the request_queue
debugfs_dir on request_queue registration. Rename the mutex also to
reflect the fact that this is used outside of the blktrace context.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
block/blk-core.c | 8 +-----
block/blk-mq-debugfs.c | 5 ----
block/blk-sysfs.c | 9 +++++++
block/blk.h | 2 --
include/linux/blkdev.h | 5 ++--
kernel/trace/blktrace.c | 58 ++++++++++++++++++-----------------------
6 files changed, 39 insertions(+), 48 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index a5126c0be777..72b102a389a5 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -51,9 +51,7 @@
#include "blk-pm.h"
#include "blk-rq-qos.h"

-#ifdef CONFIG_DEBUG_FS
struct dentry *blk_debugfs_root;
-#endif

EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
@@ -555,9 +553,7 @@ struct request_queue *__blk_alloc_queue(int node_id)

kobject_init(&q->kobj, &blk_queue_ktype);

-#ifdef CONFIG_BLK_DEV_IO_TRACE
- mutex_init(&q->blk_trace_mutex);
-#endif
+ mutex_init(&q->debugfs_mutex);
mutex_init(&q->sysfs_lock);
mutex_init(&q->sysfs_dir_lock);
spin_lock_init(&q->queue_lock);
@@ -1937,9 +1933,7 @@ int __init blk_dev_init(void)
blk_requestq_cachep = kmem_cache_create("request_queue",
sizeof(struct request_queue), 0, SLAB_PANIC, NULL);

-#ifdef CONFIG_DEBUG_FS
blk_debugfs_root = debugfs_create_dir("block", NULL);
-#endif

return 0;
}
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 15df3a36e9fa..a2800bc56fb4 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -824,9 +824,6 @@ void blk_mq_debugfs_register(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i;

- q->debugfs_dir = debugfs_create_dir(kobject_name(q->kobj.parent),
- blk_debugfs_root);
-
debugfs_create_files(q->debugfs_dir, q, blk_mq_debugfs_queue_attrs);

/*
@@ -857,9 +854,7 @@ void blk_mq_debugfs_register(struct request_queue *q)

void blk_mq_debugfs_unregister(struct request_queue *q)
{
- debugfs_remove_recursive(q->debugfs_dir);
q->sched_debugfs_dir = NULL;
- q->debugfs_dir = NULL;
}

static void blk_mq_debugfs_register_ctx(struct blk_mq_hw_ctx *hctx,
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 561624d4cc4e..be67952e7be2 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -11,6 +11,7 @@
#include <linux/blktrace_api.h>
#include <linux/blk-mq.h>
#include <linux/blk-cgroup.h>
+#include <linux/debugfs.h>

#include "blk.h"
#include "blk-mq.h"
@@ -917,6 +918,9 @@ static void blk_release_queue(struct kobject *kobj)
blk_mq_release(q);

blk_trace_shutdown(q);
+ mutex_lock(&q->debugfs_mutex);
+ debugfs_remove_recursive(q->debugfs_dir);
+ mutex_unlock(&q->debugfs_mutex);

if (queue_is_mq(q))
blk_mq_debugfs_unregister(q);
@@ -989,6 +993,11 @@ int blk_register_queue(struct gendisk *disk)
goto unlock;
}

+ mutex_lock(&q->debugfs_mutex);
+ q->debugfs_dir = debugfs_create_dir(kobject_name(q->kobj.parent),
+ blk_debugfs_root);
+ mutex_unlock(&q->debugfs_mutex);
+
if (queue_is_mq(q)) {
__blk_mq_register_dev(dev, q);
blk_mq_debugfs_register(q);
diff --git a/block/blk.h b/block/blk.h
index b5d1f0fc6547..499308c6ab3b 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -14,9 +14,7 @@
/* Max future timer expiry for timeouts */
#define BLK_MAX_TIMEOUT (5 * HZ)

-#ifdef CONFIG_DEBUG_FS
extern struct dentry *blk_debugfs_root;
-#endif

struct blk_flush_queue {
unsigned int flush_pending_idx:1;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 780d6fa94746..e70e03d2cd8c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -528,9 +528,9 @@ struct request_queue {
unsigned int sg_timeout;
unsigned int sg_reserved_size;
int node;
+ struct mutex debugfs_mutex;
#ifdef CONFIG_BLK_DEV_IO_TRACE
struct blk_trace __rcu *blk_trace;
- struct mutex blk_trace_mutex;
#endif
/*
* for flush operations
@@ -574,8 +574,9 @@ struct request_queue {
struct list_head tag_set_list;
struct bio_set bio_split;

-#ifdef CONFIG_BLK_DEBUG_FS
struct dentry *debugfs_dir;
+
+#ifdef CONFIG_BLK_DEBUG_FS
struct dentry *sched_debugfs_dir;
struct dentry *rqos_debugfs_dir;
#endif
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 098780ec018f..12e1d52f1d17 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -348,7 +348,7 @@ static int __blk_trace_remove(struct request_queue *q)
struct blk_trace *bt;

bt = rcu_replace_pointer(q->blk_trace, NULL,
- lockdep_is_held(&q->blk_trace_mutex));
+ lockdep_is_held(&q->debugfs_mutex));
if (!bt)
return -EINVAL;

@@ -362,9 +362,9 @@ int blk_trace_remove(struct request_queue *q)
{
int ret;

- mutex_lock(&q->blk_trace_mutex);
+ mutex_lock(&q->debugfs_mutex);
ret = __blk_trace_remove(q);
- mutex_unlock(&q->blk_trace_mutex);
+ mutex_unlock(&q->debugfs_mutex);

return ret;
}
@@ -483,14 +483,11 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
struct dentry *dir = NULL;
int ret;

- lockdep_assert_held(&q->blk_trace_mutex);
+ lockdep_assert_held(&q->debugfs_mutex);

if (!buts->buf_size || !buts->buf_nr)
return -EINVAL;

- if (!blk_debugfs_root)
- return -ENOENT;
-
strncpy(buts->name, name, BLKTRACE_BDEV_SIZE);
buts->name[BLKTRACE_BDEV_SIZE - 1] = '\0';

@@ -505,7 +502,7 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
* we can be.
*/
if (rcu_dereference_protected(q->blk_trace,
- lockdep_is_held(&q->blk_trace_mutex))) {
+ lockdep_is_held(&q->debugfs_mutex))) {
pr_warn("Concurrent blktraces are not allowed on %s\n",
buts->name);
return -EBUSY;
@@ -524,18 +521,15 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
if (!bt->msg_data)
goto err;

-#ifdef CONFIG_BLK_DEBUG_FS
/*
- * When tracing whole make_request drivers (multiqueue) block devices,
- * reuse the existing debugfs directory created by the block layer on
- * init. For request-based block devices, all partitions block devices,
+ * When tracing the whole disk reuse the existing debugfs directory
+ * created by the block layer on init. For partitions block devices,
* and scsi-generic block devices we create a temporary new debugfs
* directory that will be removed once the trace ends.
*/
- if (queue_is_mq(q) && bdev && bdev == bdev->bd_contains)
+ if (bdev && bdev == bdev->bd_contains)
dir = q->debugfs_dir;
else
-#endif
bt->dir = dir = debugfs_create_dir(buts->name, blk_debugfs_root);

/*
@@ -617,9 +611,9 @@ int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
{
int ret;

- mutex_lock(&q->blk_trace_mutex);
+ mutex_lock(&q->debugfs_mutex);
ret = __blk_trace_setup(q, name, dev, bdev, arg);
- mutex_unlock(&q->blk_trace_mutex);
+ mutex_unlock(&q->debugfs_mutex);

return ret;
}
@@ -665,7 +659,7 @@ static int __blk_trace_startstop(struct request_queue *q, int start)
struct blk_trace *bt;

bt = rcu_dereference_protected(q->blk_trace,
- lockdep_is_held(&q->blk_trace_mutex));
+ lockdep_is_held(&q->debugfs_mutex));
if (bt == NULL)
return -EINVAL;

@@ -705,9 +699,9 @@ int blk_trace_startstop(struct request_queue *q, int start)
{
int ret;

- mutex_lock(&q->blk_trace_mutex);
+ mutex_lock(&q->debugfs_mutex);
ret = __blk_trace_startstop(q, start);
- mutex_unlock(&q->blk_trace_mutex);
+ mutex_unlock(&q->debugfs_mutex);

return ret;
}
@@ -736,7 +730,7 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
if (!q)
return -ENXIO;

- mutex_lock(&q->blk_trace_mutex);
+ mutex_lock(&q->debugfs_mutex);

switch (cmd) {
case BLKTRACESETUP:
@@ -763,7 +757,7 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
break;
}

- mutex_unlock(&q->blk_trace_mutex);
+ mutex_unlock(&q->debugfs_mutex);
return ret;
}

@@ -774,14 +768,14 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
**/
void blk_trace_shutdown(struct request_queue *q)
{
- mutex_lock(&q->blk_trace_mutex);
+ mutex_lock(&q->debugfs_mutex);
if (rcu_dereference_protected(q->blk_trace,
- lockdep_is_held(&q->blk_trace_mutex))) {
+ lockdep_is_held(&q->debugfs_mutex))) {
__blk_trace_startstop(q, 0);
__blk_trace_remove(q);
}

- mutex_unlock(&q->blk_trace_mutex);
+ mutex_unlock(&q->debugfs_mutex);
}

#ifdef CONFIG_BLK_CGROUP
@@ -1662,7 +1656,7 @@ static int blk_trace_remove_queue(struct request_queue *q)
struct blk_trace *bt;

bt = rcu_replace_pointer(q->blk_trace, NULL,
- lockdep_is_held(&q->blk_trace_mutex));
+ lockdep_is_held(&q->debugfs_mutex));
if (bt == NULL)
return -EINVAL;

@@ -1837,10 +1831,10 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
if (q == NULL)
goto out_bdput;

- mutex_lock(&q->blk_trace_mutex);
+ mutex_lock(&q->debugfs_mutex);

bt = rcu_dereference_protected(q->blk_trace,
- lockdep_is_held(&q->blk_trace_mutex));
+ lockdep_is_held(&q->debugfs_mutex));
if (attr == &dev_attr_enable) {
ret = sprintf(buf, "%u\n", !!bt);
goto out_unlock_bdev;
@@ -1858,7 +1852,7 @@ static ssize_t sysfs_blk_trace_attr_show(struct device *dev,
ret = sprintf(buf, "%llu\n", bt->end_lba);

out_unlock_bdev:
- mutex_unlock(&q->blk_trace_mutex);
+ mutex_unlock(&q->debugfs_mutex);
out_bdput:
bdput(bdev);
out:
@@ -1901,10 +1895,10 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
if (q == NULL)
goto out_bdput;

- mutex_lock(&q->blk_trace_mutex);
+ mutex_lock(&q->debugfs_mutex);

bt = rcu_dereference_protected(q->blk_trace,
- lockdep_is_held(&q->blk_trace_mutex));
+ lockdep_is_held(&q->debugfs_mutex));
if (attr == &dev_attr_enable) {
if (!!value == !!bt) {
ret = 0;
@@ -1921,7 +1915,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
if (bt == NULL) {
ret = blk_trace_setup_queue(q, bdev);
bt = rcu_dereference_protected(q->blk_trace,
- lockdep_is_held(&q->blk_trace_mutex));
+ lockdep_is_held(&q->debugfs_mutex));
}

if (ret == 0) {
@@ -1936,7 +1930,7 @@ static ssize_t sysfs_blk_trace_attr_store(struct device *dev,
}

out_unlock_bdev:
- mutex_unlock(&q->blk_trace_mutex);
+ mutex_unlock(&q->debugfs_mutex);
out_bdput:
bdput(bdev);
out:
--
2.26.2