Driver core patches for 4.15-rc1

Here is the set of driver core / debugfs patches for 4.15-rc1.
 
 Not many here, mostly all are debugfs fixes to resolve some
 long-reported problems with files going away with references to them in
 userspace.  There's also some SPDX cleanups for the debugfs code, as
 well as a few other minor driver core changes for issues reported by
 people.
 
 All of these have been in linux-next for a week or more with no reported
 issues.
 
 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 -----BEGIN PGP SIGNATURE-----
 
 iG0EABECAC0WIQT0tgzFv3jCIUoxPcsxR9QN2y37KQUCWg2NCA8cZ3JlZ0Brcm9h
 aC5jb20ACgkQMUfUDdst+ymUNgCfYq434CFh+YtwITBNYdqkFYFf0ZAAn3qfhh2+
 M3rmZzwk2MKBvNQ2npvt
 =/8+Y
 -----END PGP SIGNATURE-----

Merge tag 'driver-core-4.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core

Pull driver core updates from Greg KH:
 "Here is the set of driver core / debugfs patches for 4.15-rc1.

  Not many here, mostly all are debugfs fixes to resolve some
  long-reported problems with files going away with references to them
  in userspace. There's also some SPDX cleanups for the debugfs code, as
  well as a few other minor driver core changes for issues reported by
  people.

  All of these have been in linux-next for a week or more with no
  reported issues"

* tag 'driver-core-4.15-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core:
  driver core: Fix device link deferred probe
  debugfs: Remove redundant license text
  debugfs: add SPDX identifiers to all debugfs files
  debugfs: defer debugfs_fsdata allocation to first usage
  debugfs: call debugfs_real_fops() only after debugfs_file_get()
  debugfs: purge obsolete SRCU based removal protection
  IB/hfi1: convert to debugfs_file_get() and -put()
  debugfs: convert to debugfs_file_get() and -put()
  debugfs: debugfs_real_fops(): drop __must_hold sparse annotation
  debugfs: implement per-file removal protection
  debugfs: add support for more elaborate ->d_fsdata
  driver core: Move device_links_purge() after bus_remove_device()
  arch_topology: Fix section miss match warning due to free_raw_capacity()
  driver-core: pr_err() strings should end with newlines

drivers/base/arch_topology.c

@@ -105,7 +105,7 @@ subsys_initcall(register_cpu_capacity_sysctl);
 static u32 capacity_scale;
 static u32 *raw_capacity;
 
-static int __init free_raw_capacity(void)
+static int free_raw_capacity(void)
 {
 	kfree(raw_capacity);
 	raw_capacity = NULL;

drivers/base/core.c

@@ -1958,7 +1958,6 @@ void device_del(struct device *dev)
 		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
 					     BUS_NOTIFY_DEL_DEVICE, dev);
 
-	device_links_purge(dev);
 	dpm_sysfs_remove(dev);
 	if (parent)
 		klist_del(&dev->p->knode_parent);
@@ -1986,6 +1985,7 @@ void device_del(struct device *dev)
 	device_pm_remove(dev);
 	driver_deferred_probe_del(dev);
 	device_remove_properties(dev);
+	device_links_purge(dev);
 
 	/* Notify the platform of the removal, in case they
 	 * need to do anything...

drivers/base/dd.c

@@ -350,6 +350,15 @@ EXPORT_SYMBOL_GPL(device_bind_driver);
 static atomic_t probe_count = ATOMIC_INIT(0);
 static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue);
 
+static void driver_deferred_probe_add_trigger(struct device *dev,
+					      int local_trigger_count)
+{
+	driver_deferred_probe_add(dev);
+	/* Did a trigger occur while probing? Need to re-trigger if yes */
+	if (local_trigger_count != atomic_read(&deferred_trigger_count))
+		driver_deferred_probe_trigger();
+}
+
 static int really_probe(struct device *dev, struct device_driver *drv)
 {
 	int ret = -EPROBE_DEFER;
@@ -369,6 +378,8 @@ static int really_probe(struct device *dev, struct device_driver *drv)
 	}
 
 	ret = device_links_check_suppliers(dev);
+	if (ret == -EPROBE_DEFER)
+		driver_deferred_probe_add_trigger(dev, local_trigger_count);
 	if (ret)
 		return ret;
 
@@ -470,10 +481,7 @@ pinctrl_bind_failed:
 	case -EPROBE_DEFER:
 		/* Driver requested deferred probing */
 		dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name);
-		driver_deferred_probe_add(dev);
+		driver_deferred_probe_add_trigger(dev, local_trigger_count);
-		/* Did a trigger occur while probing? Need to re-trigger if yes */
-		if (local_trigger_count != atomic_read(&deferred_trigger_count))
-			driver_deferred_probe_trigger();
 		break;
 	case -ENODEV:
 	case -ENXIO:

drivers/base/test/test_async_driver_probe.c

@@ -64,7 +64,7 @@ static int __init test_async_probe_init(void)
 						      NULL, 0);
 	if (IS_ERR(async_dev_1)) {
 		error = PTR_ERR(async_dev_1);
-		pr_err("failed to create async_dev_1: %d", error);
+		pr_err("failed to create async_dev_1: %d\n", error);
 		return error;
 	}
 
@@ -91,7 +91,7 @@ static int __init test_async_probe_init(void)
 						      NULL, 0);
 	if (IS_ERR(async_dev_2)) {
 		error = PTR_ERR(async_dev_2);
-		pr_err("failed to create async_dev_2: %d", error);
+		pr_err("failed to create async_dev_2: %d\n", error);
 		goto err_unregister_async_driver;
 	}
 
@@ -118,7 +118,7 @@ static int __init test_async_probe_init(void)
 						     NULL, 0);
 	if (IS_ERR(sync_dev_1)) {
 		error = PTR_ERR(sync_dev_1);
-		pr_err("failed to create sync_dev_1: %d", error);
+		pr_err("failed to create sync_dev_1: %d\n", error);
 		goto err_unregister_sync_driver;
 	}
 

drivers/infiniband/hw/hfi1/debugfs.c

@@ -71,13 +71,13 @@ static ssize_t hfi1_seq_read(
 	loff_t *ppos)
 {
 	struct dentry *d = file->f_path.dentry;
-	int srcu_idx;
 	ssize_t r;
 
-	r = debugfs_use_file_start(d, &srcu_idx);
+	r = debugfs_file_get(d);
-	if (likely(!r))
+	if (unlikely(r))
-		r = seq_read(file, buf, size, ppos);
+		return r;
-	debugfs_use_file_finish(srcu_idx);
+	r = seq_read(file, buf, size, ppos);
+	debugfs_file_put(d);
 	return r;
 }
 
@@ -87,13 +87,13 @@ static loff_t hfi1_seq_lseek(
 	int whence)
 {
 	struct dentry *d = file->f_path.dentry;
-	int srcu_idx;
 	loff_t r;
 
-	r = debugfs_use_file_start(d, &srcu_idx);
+	r = debugfs_file_get(d);
-	if (likely(!r))
+	if (unlikely(r))
-		r = seq_lseek(file, offset, whence);
+		return r;
-	debugfs_use_file_finish(srcu_idx);
+	r = seq_lseek(file, offset, whence);
+	debugfs_file_put(d);
 	return r;
 }
 

fs/debugfs/file.c

@@ -1,16 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  *  file.c - part of debugfs, a tiny little debug file system
  *
  *  Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
  *  Copyright (C) 2004 IBM Inc.
  *
- *	This program is free software; you can redistribute it and/or
- *	modify it under the terms of the GNU General Public License version
- *	2 as published by the Free Software Foundation.
- *
  *  debugfs is for people to use instead of /proc or /sys.
  *  See Documentation/filesystems/ for more details.
- *
  */
 
 #include <linux/module.h>
@@ -22,7 +18,6 @@
 #include <linux/slab.h>
 #include <linux/atomic.h>
 #include <linux/device.h>
-#include <linux/srcu.h>
 #include <asm/poll.h>
 
 #include "internal.h"
@@ -48,66 +43,108 @@ const struct file_operations debugfs_noop_file_operations = {
 	.llseek =	noop_llseek,
 };
 
+#define F_DENTRY(filp) ((filp)->f_path.dentry)
+
+const struct file_operations *debugfs_real_fops(const struct file *filp)
+{
+	struct debugfs_fsdata *fsd = F_DENTRY(filp)->d_fsdata;
+
+	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT) {
+		/*
+		 * Urgh, we've been called w/o a protecting
+		 * debugfs_file_get().
+		 */
+		WARN_ON(1);
+		return NULL;
+	}
+
+	return fsd->real_fops;
+}
+EXPORT_SYMBOL_GPL(debugfs_real_fops);
+
 /**
- * debugfs_use_file_start - mark the beginning of file data access
+ * debugfs_file_get - mark the beginning of file data access
  * @dentry: the dentry object whose data is being accessed.
- * @srcu_idx: a pointer to some memory to store a SRCU index in.
  *
- * Up to a matching call to debugfs_use_file_finish(), any
+ * Up to a matching call to debugfs_file_put(), any successive call
- * successive call into the file removing functions debugfs_remove()
+ * into the file removing functions debugfs_remove() and
- * and debugfs_remove_recursive() will block. Since associated private
+ * debugfs_remove_recursive() will block. Since associated private
  * file data may only get freed after a successful return of any of
  * the removal functions, you may safely access it after a successful
- * call to debugfs_use_file_start() without worrying about
+ * call to debugfs_file_get() without worrying about lifetime issues.
- * lifetime issues.
  *
  * If -%EIO is returned, the file has already been removed and thus,
  * it is not safe to access any of its data. If, on the other hand,
  * it is allowed to access the file data, zero is returned.
- *
- * Regardless of the return code, any call to
- * debugfs_use_file_start() must be followed by a matching call
- * to debugfs_use_file_finish().
  */
-int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)
+int debugfs_file_get(struct dentry *dentry)
-	__acquires(&debugfs_srcu)
 {
-	*srcu_idx = srcu_read_lock(&debugfs_srcu);
+	struct debugfs_fsdata *fsd;
-	barrier();
+	void *d_fsd;
+
+	d_fsd = READ_ONCE(dentry->d_fsdata);
+	if (!((unsigned long)d_fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)) {
+		fsd = d_fsd;
+	} else {
+		fsd = kmalloc(sizeof(*fsd), GFP_KERNEL);
+		if (!fsd)
+			return -ENOMEM;
+
+		fsd->real_fops = (void *)((unsigned long)d_fsd &
+					~DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
+		refcount_set(&fsd->active_users, 1);
+		init_completion(&fsd->active_users_drained);
+		if (cmpxchg(&dentry->d_fsdata, d_fsd, fsd) != d_fsd) {
+			kfree(fsd);
+			fsd = READ_ONCE(dentry->d_fsdata);
+		}
+	}
+
+	/*
+	 * In case of a successful cmpxchg() above, this check is
+	 * strictly necessary and must follow it, see the comment in
+	 * __debugfs_remove_file().
+	 * OTOH, if the cmpxchg() hasn't been executed or wasn't
+	 * successful, this serves the purpose of not starving
+	 * removers.
+	 */
 	if (d_unlinked(dentry))
 		return -EIO;
+
+	if (!refcount_inc_not_zero(&fsd->active_users))
+		return -EIO;
+
 	return 0;
 }
-EXPORT_SYMBOL_GPL(debugfs_use_file_start);
+EXPORT_SYMBOL_GPL(debugfs_file_get);
 
 /**
- * debugfs_use_file_finish - mark the end of file data access
+ * debugfs_file_put - mark the end of file data access
- * @srcu_idx: the SRCU index "created" by a former call to
+ * @dentry: the dentry object formerly passed to
- *            debugfs_use_file_start().
+ *          debugfs_file_get().
  *
  * Allow any ongoing concurrent call into debugfs_remove() or
  * debugfs_remove_recursive() blocked by a former call to
- * debugfs_use_file_start() to proceed and return to its caller.
+ * debugfs_file_get() to proceed and return to its caller.
  */
-void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu)
+void debugfs_file_put(struct dentry *dentry)
 {
-	srcu_read_unlock(&debugfs_srcu, srcu_idx);
+	struct debugfs_fsdata *fsd = READ_ONCE(dentry->d_fsdata);
-}
-EXPORT_SYMBOL_GPL(debugfs_use_file_finish);
 
-#define F_DENTRY(filp) ((filp)->f_path.dentry)
+	if (refcount_dec_and_test(&fsd->active_users))
+		complete(&fsd->active_users_drained);
+}
+EXPORT_SYMBOL_GPL(debugfs_file_put);
 
 static int open_proxy_open(struct inode *inode, struct file *filp)
 {
-	const struct dentry *dentry = F_DENTRY(filp);
+	struct dentry *dentry = F_DENTRY(filp);
 	const struct file_operations *real_fops = NULL;
-	int srcu_idx, r;
+	int r;
 
-	r = debugfs_use_file_start(dentry, &srcu_idx);
+	r = debugfs_file_get(dentry);
-	if (r) {
+	if (r)
-		r = -ENOENT;
+		return r == -EIO ? -ENOENT : r;
-		goto out;
-	}
 
 	real_fops = debugfs_real_fops(filp);
 	real_fops = fops_get(real_fops);
@@ -124,7 +161,7 @@ static int open_proxy_open(struct inode *inode, struct file *filp)
 		r = real_fops->open(inode, filp);
 
 out:
-	debugfs_use_file_finish(srcu_idx);
+	debugfs_file_put(dentry);
 	return r;
 }
 
@@ -138,16 +175,16 @@ const struct file_operations debugfs_open_proxy_file_operations = {
 #define FULL_PROXY_FUNC(name, ret_type, filp, proto, args)		\
 static ret_type full_proxy_ ## name(proto)				\
 {									\
-	const struct dentry *dentry = F_DENTRY(filp);			\
+	struct dentry *dentry = F_DENTRY(filp);			\
-	const struct file_operations *real_fops =			\
+	const struct file_operations *real_fops;			\
-		debugfs_real_fops(filp);				\
-	int srcu_idx;							\
 	ret_type r;							\
 									\
-	r = debugfs_use_file_start(dentry, &srcu_idx);			\
+	r = debugfs_file_get(dentry);					\
-	if (likely(!r))						\
+	if (unlikely(r))						\
-		r = real_fops->name(args);				\
+		return r;						\
-	debugfs_use_file_finish(srcu_idx);				\
+	real_fops = debugfs_real_fops(filp);				\
+	r = real_fops->name(args);					\
+	debugfs_file_put(dentry);					\
 	return r;							\
 }
 
@@ -172,18 +209,16 @@ FULL_PROXY_FUNC(unlocked_ioctl, long, filp,
 static unsigned int full_proxy_poll(struct file *filp,
 				struct poll_table_struct *wait)
 {
-	const struct dentry *dentry = F_DENTRY(filp);
+	struct dentry *dentry = F_DENTRY(filp);
-	const struct file_operations *real_fops = debugfs_real_fops(filp);
-	int srcu_idx;
 	unsigned int r = 0;
+	const struct file_operations *real_fops;
 
-	if (debugfs_use_file_start(dentry, &srcu_idx)) {
+	if (debugfs_file_get(dentry))
-		debugfs_use_file_finish(srcu_idx);
 		return POLLHUP;
-	}
 
+	real_fops = debugfs_real_fops(filp);
 	r = real_fops->poll(filp, wait);
-	debugfs_use_file_finish(srcu_idx);
+	debugfs_file_put(dentry);
 	return r;
 }
 
@@ -227,16 +262,14 @@ static void __full_proxy_fops_init(struct file_operations *proxy_fops,
 
 static int full_proxy_open(struct inode *inode, struct file *filp)
 {
-	const struct dentry *dentry = F_DENTRY(filp);
+	struct dentry *dentry = F_DENTRY(filp);
 	const struct file_operations *real_fops = NULL;
 	struct file_operations *proxy_fops = NULL;
-	int srcu_idx, r;
+	int r;
 
-	r = debugfs_use_file_start(dentry, &srcu_idx);
+	r = debugfs_file_get(dentry);
-	if (r) {
+	if (r)
-		r = -ENOENT;
+		return r == -EIO ? -ENOENT : r;
-		goto out;
-	}
 
 	real_fops = debugfs_real_fops(filp);
 	real_fops = fops_get(real_fops);
@@ -274,7 +307,7 @@ free_proxy:
 	kfree(proxy_fops);
 	fops_put(real_fops);
 out:
-	debugfs_use_file_finish(srcu_idx);
+	debugfs_file_put(dentry);
 	return r;
 }
 
@@ -285,13 +318,14 @@ const struct file_operations debugfs_full_proxy_file_operations = {
 ssize_t debugfs_attr_read(struct file *file, char __user *buf,
 			size_t len, loff_t *ppos)
 {
+	struct dentry *dentry = F_DENTRY(file);
 	ssize_t ret;
-	int srcu_idx;
 
-	ret = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);
+	ret = debugfs_file_get(dentry);
-	if (likely(!ret))
+	if (unlikely(ret))
-		ret = simple_attr_read(file, buf, len, ppos);
+		return ret;
-	debugfs_use_file_finish(srcu_idx);
+	ret = simple_attr_read(file, buf, len, ppos);
+	debugfs_file_put(dentry);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(debugfs_attr_read);
@@ -299,13 +333,14 @@ EXPORT_SYMBOL_GPL(debugfs_attr_read);
 ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
 			 size_t len, loff_t *ppos)
 {
+	struct dentry *dentry = F_DENTRY(file);
 	ssize_t ret;
-	int srcu_idx;
 
-	ret = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);
+	ret = debugfs_file_get(dentry);
-	if (likely(!ret))
+	if (unlikely(ret))
-		ret = simple_attr_write(file, buf, len, ppos);
+		return ret;
-	debugfs_use_file_finish(srcu_idx);
+	ret = simple_attr_write(file, buf, len, ppos);
+	debugfs_file_put(dentry);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(debugfs_attr_write);
@@ -739,14 +774,14 @@ ssize_t debugfs_read_file_bool(struct file *file, char __user *user_buf,
 {
 	char buf[3];
 	bool val;
-	int r, srcu_idx;
+	int r;
+	struct dentry *dentry = F_DENTRY(file);
 
-	r = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);
+	r = debugfs_file_get(dentry);
-	if (likely(!r))
+	if (unlikely(r))
-		val = *(bool *)file->private_data;
-	debugfs_use_file_finish(srcu_idx);
-	if (r)
 		return r;
+	val = *(bool *)file->private_data;
+	debugfs_file_put(dentry);
 
 	if (val)
 		buf[0] = 'Y';
@@ -764,8 +799,9 @@ ssize_t debugfs_write_file_bool(struct file *file, const char __user *user_buf,
 	char buf[32];
 	size_t buf_size;
 	bool bv;
-	int r, srcu_idx;
+	int r;
 	bool *val = file->private_data;
+	struct dentry *dentry = F_DENTRY(file);
 
 	buf_size = min(count, (sizeof(buf)-1));
 	if (copy_from_user(buf, user_buf, buf_size))
@@ -773,12 +809,11 @@ ssize_t debugfs_write_file_bool(struct file *file, const char __user *user_buf,
 
 	buf[buf_size] = '\0';
 	if (strtobool(buf, &bv) == 0) {
-		r = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);
+		r = debugfs_file_get(dentry);
-		if (likely(!r))
+		if (unlikely(r))
-			*val = bv;
-		debugfs_use_file_finish(srcu_idx);
-		if (r)
 			return r;
+		*val = bv;
+		debugfs_file_put(dentry);
 	}
 
 	return count;
@@ -840,14 +875,15 @@ static ssize_t read_file_blob(struct file *file, char __user *user_buf,
 			      size_t count, loff_t *ppos)
 {
 	struct debugfs_blob_wrapper *blob = file->private_data;
+	struct dentry *dentry = F_DENTRY(file);
 	ssize_t r;
-	int srcu_idx;
 
-	r = debugfs_use_file_start(F_DENTRY(file), &srcu_idx);
+	r = debugfs_file_get(dentry);
-	if (likely(!r))
+	if (unlikely(r))
-		r = simple_read_from_buffer(user_buf, count, ppos, blob->data,
+		return r;
-					blob->size);
+	r = simple_read_from_buffer(user_buf, count, ppos, blob->data,
-	debugfs_use_file_finish(srcu_idx);
+				blob->size);
+	debugfs_file_put(dentry);
 	return r;
 }
 

fs/debugfs/inode.c

@@ -1,16 +1,12 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  *  inode.c - part of debugfs, a tiny little debug file system
  *
  *  Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
  *  Copyright (C) 2004 IBM Inc.
  *
- *	This program is free software; you can redistribute it and/or
- *	modify it under the terms of the GNU General Public License version
- *	2 as published by the Free Software Foundation.
- *
  *  debugfs is for people to use instead of /proc or /sys.
  *  See ./Documentation/core-api/kernel-api.rst for more details.
- *
  */
 
 #include <linux/module.h>
@@ -27,14 +23,11 @@
 #include <linux/parser.h>
 #include <linux/magic.h>
 #include <linux/slab.h>
-#include <linux/srcu.h>
 
 #include "internal.h"
 
 #define DEBUGFS_DEFAULT_MODE	0700
 
-DEFINE_SRCU(debugfs_srcu);
-
 static struct vfsmount *debugfs_mount;
 static int debugfs_mount_count;
 static bool debugfs_registered;
@@ -185,6 +178,14 @@ static const struct super_operations debugfs_super_operations = {
 	.evict_inode	= debugfs_evict_inode,
 };
 
+static void debugfs_release_dentry(struct dentry *dentry)
+{
+	void *fsd = dentry->d_fsdata;
+
+	if (!((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
+		kfree(dentry->d_fsdata);
+}
+
 static struct vfsmount *debugfs_automount(struct path *path)
 {
 	debugfs_automount_t f;
@@ -194,6 +195,7 @@ static struct vfsmount *debugfs_automount(struct path *path)
 
 static const struct dentry_operations debugfs_dops = {
 	.d_delete = always_delete_dentry,
+	.d_release = debugfs_release_dentry,
 	.d_automount = debugfs_automount,
 };
 
@@ -358,7 +360,8 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
 	inode->i_private = data;
 
 	inode->i_fop = proxy_fops;
-	dentry->d_fsdata = (void *)real_fops;
+	dentry->d_fsdata = (void *)((unsigned long)real_fops |
+				DEBUGFS_FSDATA_IS_REAL_FOPS_BIT);
 
 	d_instantiate(dentry, inode);
 	fsnotify_create(d_inode(dentry->d_parent), dentry);
@@ -615,18 +618,43 @@ struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
 }
 EXPORT_SYMBOL_GPL(debugfs_create_symlink);
 
+static void __debugfs_remove_file(struct dentry *dentry, struct dentry *parent)
+{
+	struct debugfs_fsdata *fsd;
+
+	simple_unlink(d_inode(parent), dentry);
+	d_delete(dentry);
+
+	/*
+	 * Paired with the closing smp_mb() implied by a successful
+	 * cmpxchg() in debugfs_file_get(): either
+	 * debugfs_file_get() must see a dead dentry or we must see a
+	 * debugfs_fsdata instance at ->d_fsdata here (or both).
+	 */
+	smp_mb();
+	fsd = READ_ONCE(dentry->d_fsdata);
+	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
+		return;
+	if (!refcount_dec_and_test(&fsd->active_users))
+		wait_for_completion(&fsd->active_users_drained);
+}
+
 static int __debugfs_remove(struct dentry *dentry, struct dentry *parent)
 {
 	int ret = 0;
 
 	if (simple_positive(dentry)) {
 		dget(dentry);
-		if (d_is_dir(dentry))
+		if (!d_is_reg(dentry)) {
-			ret = simple_rmdir(d_inode(parent), dentry);
+			if (d_is_dir(dentry))
-		else
+				ret = simple_rmdir(d_inode(parent), dentry);
-			simple_unlink(d_inode(parent), dentry);
+			else
-		if (!ret)
+				simple_unlink(d_inode(parent), dentry);
-			d_delete(dentry);
+			if (!ret)
+				d_delete(dentry);
+		} else {
+			__debugfs_remove_file(dentry, parent);
+		}
 		dput(dentry);
 	}
 	return ret;
@@ -660,8 +688,6 @@ void debugfs_remove(struct dentry *dentry)
 	inode_unlock(d_inode(parent));
 	if (!ret)
 		simple_release_fs(&debugfs_mount, &debugfs_mount_count);
-
-	synchronize_srcu(&debugfs_srcu);
 }
 EXPORT_SYMBOL_GPL(debugfs_remove);
 
@@ -735,8 +761,6 @@ void debugfs_remove_recursive(struct dentry *dentry)
 	if (!__debugfs_remove(child, parent))
 		simple_release_fs(&debugfs_mount, &debugfs_mount_count);
 	inode_unlock(d_inode(parent));
-
-	synchronize_srcu(&debugfs_srcu);
 }
 EXPORT_SYMBOL_GPL(debugfs_remove_recursive);
 

fs/debugfs/internal.h

@@ -1,12 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  *  internal.h - declarations internal to debugfs
  *
  *  Copyright (C) 2016 Nicolai Stange <nicstange@gmail.com>
- *
- *	This program is free software; you can redistribute it and/or
- *	modify it under the terms of the GNU General Public License version
- *	2 as published by the Free Software Foundation.
- *
  */
 
 #ifndef _DEBUGFS_INTERNAL_H_
@@ -19,4 +15,18 @@ extern const struct file_operations debugfs_noop_file_operations;
 extern const struct file_operations debugfs_open_proxy_file_operations;
 extern const struct file_operations debugfs_full_proxy_file_operations;
 
+struct debugfs_fsdata {
+	const struct file_operations *real_fops;
+	refcount_t active_users;
+	struct completion active_users_drained;
+};
+
+/*
+ * A dentry's ->d_fsdata either points to the real fops or to a
+ * dynamically allocated debugfs_fsdata instance.
+ * In order to distinguish between these two cases, a real fops
+ * pointer gets its lowest bit set.
+ */
+#define DEBUGFS_FSDATA_IS_REAL_FOPS_BIT BIT(0)
+
 #endif /* _DEBUGFS_INTERNAL_H_ */

include/linux/debugfs.h

@@ -1,13 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  *  debugfs.h - a tiny little debug file system
  *
  *  Copyright (C) 2004 Greg Kroah-Hartman <greg@kroah.com>
  *  Copyright (C) 2004 IBM Inc.
  *
- *	This program is free software; you can redistribute it and/or
- *	modify it under the terms of the GNU General Public License version
- *	2 as published by the Free Software Foundation.
- *
  *  debugfs is for people to use instead of /proc or /sys.
  *  See Documentation/filesystems/ for more details.
  */
@@ -23,7 +20,6 @@
 
 struct device;
 struct file_operations;
-struct srcu_struct;
 
 struct debugfs_blob_wrapper {
 	void *data;
@@ -43,25 +39,6 @@ struct debugfs_regset32 {
 
 extern struct dentry *arch_debugfs_dir;
 
-extern struct srcu_struct debugfs_srcu;
-
-/**
- * debugfs_real_fops - getter for the real file operation
- * @filp: a pointer to a struct file
- *
- * Must only be called under the protection established by
- * debugfs_use_file_start().
- */
-static inline const struct file_operations *debugfs_real_fops(const struct file *filp)
-	__must_hold(&debugfs_srcu)
-{
-	/*
-	 * Neither the pointer to the struct file_operations, nor its
-	 * contents ever change -- srcu_dereference() is not needed here.
-	 */
-	return filp->f_path.dentry->d_fsdata;
-}
-
 #define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)		\
 static int __fops ## _open(struct inode *inode, struct file *file)	\
 {									\
@@ -107,10 +84,10 @@ struct dentry *debugfs_create_automount(const char *name,
 void debugfs_remove(struct dentry *dentry);
 void debugfs_remove_recursive(struct dentry *dentry);
 
-int debugfs_use_file_start(const struct dentry *dentry, int *srcu_idx)
+const struct file_operations *debugfs_real_fops(const struct file *filp);
-	__acquires(&debugfs_srcu);
 
-void debugfs_use_file_finish(int srcu_idx) __releases(&debugfs_srcu);
+int debugfs_file_get(struct dentry *dentry);
+void debugfs_file_put(struct dentry *dentry);
 
 ssize_t debugfs_attr_read(struct file *file, char __user *buf,
 			size_t len, loff_t *ppos);
@@ -239,15 +216,12 @@ static inline void debugfs_remove(struct dentry *dentry)
 static inline void debugfs_remove_recursive(struct dentry *dentry)
 { }
 
-static inline int debugfs_use_file_start(const struct dentry *dentry,
+static inline int debugfs_file_get(struct dentry *dentry)
-					int *srcu_idx)
-	__acquires(&debugfs_srcu)
 {
 	return 0;
 }
 
-static inline void debugfs_use_file_finish(int srcu_idx)
+static inline void debugfs_file_put(struct dentry *dentry)
-	__releases(&debugfs_srcu)
 { }
 
 static inline ssize_t debugfs_attr_read(struct file *file, char __user *buf,

lib/Kconfig.debug

@@ -280,7 +280,6 @@ config PAGE_OWNER
 
 config DEBUG_FS
 	bool "Debug Filesystem"
-	select SRCU
 	help
 	  debugfs is a virtual file system that kernel developers use to put
 	  debugging files into.  Enable this option to be able to read and