[PATCH v2 0/6] fixes for debugfs/wireless locking issue

[PATCH v2 0/6] fixes for debugfs/wireless locking issue

[Johannes Berg]

There's a locking issue in wireless where it takes a lock inside
a debugfs file handler that's also taken around the removal of
the debugfs file, and this causes a deadlock due to the proxy
object use. Fixing the debugfs removal is tricky because some
of the objects represented there fundamentally are deleted with
the lock held. Not taking the lock in the debugfs file is also
not really the right thing to do. Therefore, right now, the only
way to fix this would be to not have the debugfs files entirely,
but that isn't really helpful either.

Thus, here's a way to fix it that doesn't just remove the files.

The first patch is just a consistency thing in debugfs, right now
directory dentries don't have d_fsdata, normal file use the proxy
fops object, and automount uses the original autmount (function)
pointer, no proxy object. This is an issue if an automount dentry
were ever removed, which right now it isn't as far as I can tell,
but it still makes little sense, so fix it here by also allocating
an object for it, just not with real_fops making it a proxy, but
with the automount pointer inside.

The second patch annotates debugfs with lockdep to actually find
deadlock scenarios such as the one in wireless, indeed with that
and accessing one of the affected debugfs files, lockdep detects
the situation.

The third patch introduces a concept of 'cancellation', whereby a
debugfs file handler that is "long-running" may enter (and later
leave, of course) a cancellation section, where a function call
is made when the file is removed while the handler is running, and
the cancellation function can then abort the handling. This is
pretty generic so far.

The later patches (and I assume those would go through the wireless
tree) then fix the locking issue by declaring that the work that's
going to happen under lock is "long-running" per the above, and
setting up a cancellation. The way it works is that it actually
defers the real handling to a workqueue but then waits for it, but
that waiting can be aborted (and the work stopped) if the file is
removed before the work was able to run, thus fixing the deadlock.

I hope this is an acceptable compromise in terms of functionality
in debugfs vs. the user. It'd be possible to set up something of
the same sort in debugfs, but I feel the cancellation API is more
generic and thus more useful, and the actual details of what's in
the actual file handlers don't matter then.

johannes

[PATCH v2 1/6] debugfs: fix automount d_fsdata usage

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

debugfs_create_automount() stores a function pointer in d_fsdata,
but since commit 7c8d469877b1 ("debugfs: add support for more
elaborate ->d_fsdata") debugfs_release_dentry() will free it, now
conditionally on DEBUGFS_FSDATA_IS_REAL_FOPS_BIT, but that's not
set for the function pointer in automount. As a result, removing
an automount dentry would attempt to free the function pointer.
Luckily, the only user of this (tracing) never removes it.

Nevertheless, it's safer if we just handle the fsdata in one way,
namely either DEBUGFS_FSDATA_IS_REAL_FOPS_BIT or allocated. Thus,
change the automount to allocate it, and use the real_fops in the
data to indicate whether or not automount is filled, rather than
adding a type tag. At least for now this isn't actually needed,
but the next changes will require it.

Also check in debugfs_file_get() that it gets only called
on regular files, just to make things clearer.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
v2: add missing kfree() pointed out by smatch
---
 fs/debugfs/file.c     |  8 ++++++++
 fs/debugfs/inode.c    | 27 ++++++++++++++++++++-------
 fs/debugfs/internal.h | 10 ++++++++--
 3 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 87b3753aa4b1..e00189aebbf4 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -84,6 +84,14 @@ int debugfs_file_get(struct dentry *dentry)
 	struct debugfs_fsdata *fsd;
 	void *d_fsd;
 
+	/*
+	 * This could only happen if some debugfs user erroneously calls
+	 * debugfs_file_get() on a dentry that isn't even a file, let
+	 * them know about it.
+	 */
+	if (WARN_ON(!d_is_reg(dentry)))
+		return -EINVAL;
+
 	d_fsd = READ_ONCE(dentry->d_fsdata);
 	if (!((unsigned long)d_fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)) {
 		fsd = d_fsd;
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 83e57e9f9fa0..dcde4199a625 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -236,17 +236,19 @@ static const struct super_operations debugfs_super_operations = {
 
 static void debugfs_release_dentry(struct dentry *dentry)
 {
-	void *fsd = dentry->d_fsdata;
+	struct debugfs_fsdata *fsd = dentry->d_fsdata;
 
-	if (!((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT))
-		kfree(dentry->d_fsdata);
+	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
+		return;
+
+	kfree(fsd);
 }
 
 static struct vfsmount *debugfs_automount(struct path *path)
 {
-	debugfs_automount_t f;
-	f = (debugfs_automount_t)path->dentry->d_fsdata;
-	return f(path->dentry, d_inode(path->dentry)->i_private);
+	struct debugfs_fsdata *fsd = path->dentry->d_fsdata;
+
+	return fsd->automount(path->dentry, d_inode(path->dentry)->i_private);
 }
 
 static const struct dentry_operations debugfs_dops = {
@@ -634,13 +636,23 @@ struct dentry *debugfs_create_automount(const char *name,
 					void *data)
 {
 	struct dentry *dentry = start_creating(name, parent);
+	struct debugfs_fsdata *fsd;
 	struct inode *inode;
 
 	if (IS_ERR(dentry))
 		return dentry;
 
+	fsd = kzalloc(sizeof(*fsd), GFP_KERNEL);
+	if (!fsd) {
+		failed_creating(dentry);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	fsd->automount = f;
+
 	if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
 		failed_creating(dentry);
+		kfree(fsd);
 		return ERR_PTR(-EPERM);
 	}
 
@@ -648,13 +660,14 @@ struct dentry *debugfs_create_automount(const char *name,
 	if (unlikely(!inode)) {
 		pr_err("out of free dentries, can not create automount '%s'\n",
 		       name);
+		kfree(fsd);
 		return failed_creating(dentry);
 	}
 
 	make_empty_dir_inode(inode);
 	inode->i_flags |= S_AUTOMOUNT;
 	inode->i_private = data;
-	dentry->d_fsdata = (void *)f;
+	dentry->d_fsdata = fsd;
 	/* directory inodes start off with i_nlink == 2 (for "." entry) */
 	inc_nlink(inode);
 	d_instantiate(dentry, inode);
diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h
index 92af8ae31313..f7c489b5a368 100644
--- a/fs/debugfs/internal.h
+++ b/fs/debugfs/internal.h
@@ -17,8 +17,14 @@ 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;
+	union {
+		/* automount_fn is used when real_fops is NULL */
+		debugfs_automount_t automount;
+		struct {
+			refcount_t active_users;
+			struct completion active_users_drained;
+		};
+	};
 };
 
 /*
-- 
2.42.0

Re: [PATCH v2 1/6] debugfs: fix automount d_fsdata usage

[Greg Kroah-Hartman]

On Fri, Nov 24, 2023 at 05:25:24PM +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
> 
> debugfs_create_automount() stores a function pointer in d_fsdata,
> but since commit 7c8d469877b1 ("debugfs: add support for more
> elaborate ->d_fsdata") debugfs_release_dentry() will free it, now
> conditionally on DEBUGFS_FSDATA_IS_REAL_FOPS_BIT, but that's not
> set for the function pointer in automount. As a result, removing
> an automount dentry would attempt to free the function pointer.
> Luckily, the only user of this (tracing) never removes it.
> 
> Nevertheless, it's safer if we just handle the fsdata in one way,
> namely either DEBUGFS_FSDATA_IS_REAL_FOPS_BIT or allocated. Thus,
> change the automount to allocate it, and use the real_fops in the
> data to indicate whether or not automount is filled, rather than
> adding a type tag. At least for now this isn't actually needed,
> but the next changes will require it.
> 
> Also check in debugfs_file_get() that it gets only called
> on regular files, just to make things clearer.
> 
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> ---
> v2: add missing kfree() pointed out by smatch

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Re: [PATCH v2 1/6] debugfs: fix automount d_fsdata usage

[Johannes Berg]

On Sat, 2023-11-25 at 14:48 +0000, Greg Kroah-Hartman wrote:
> On Fri, Nov 24, 2023 at 05:25:24PM +0100, Johannes Berg wrote:
> > From: Johannes Berg <johannes.berg@intel.com>
> > 
> > debugfs_create_automount() stores a function pointer in d_fsdata,
> > but since commit 7c8d469877b1 ("debugfs: add support for more
> > elaborate ->d_fsdata") debugfs_release_dentry() will free it, now
> > conditionally on DEBUGFS_FSDATA_IS_REAL_FOPS_BIT, but that's not
> > set for the function pointer in automount. As a result, removing
> > an automount dentry would attempt to free the function pointer.
> > Luckily, the only user of this (tracing) never removes it.
> > 
> > Nevertheless, it's safer if we just handle the fsdata in one way,
> > namely either DEBUGFS_FSDATA_IS_REAL_FOPS_BIT or allocated. Thus,
> > change the automount to allocate it, and use the real_fops in the
> > data to indicate whether or not automount is filled, rather than
> > adding a type tag. At least for now this isn't actually needed,
> > but the next changes will require it.
> > 
> > Also check in debugfs_file_get() that it gets only called
> > on regular files, just to make things clearer.
> > 
> > Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> > ---
> > v2: add missing kfree() pointed out by smatch
> 
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

I have to fix the Kconfig issue in one of the later (wireless) patches,
but does that mean you'd actually prefer the debugfs changes go through
the wireless tree, together with the code using it?

Thanks,
johannes

Re: [PATCH v2 1/6] debugfs: fix automount d_fsdata usage

[Greg Kroah-Hartman]

On Sat, Nov 25, 2023 at 07:31:47PM +0100, Johannes Berg wrote:
> On Sat, 2023-11-25 at 14:48 +0000, Greg Kroah-Hartman wrote:
> > On Fri, Nov 24, 2023 at 05:25:24PM +0100, Johannes Berg wrote:
> > > From: Johannes Berg <johannes.berg@intel.com>
> > > 
> > > debugfs_create_automount() stores a function pointer in d_fsdata,
> > > but since commit 7c8d469877b1 ("debugfs: add support for more
> > > elaborate ->d_fsdata") debugfs_release_dentry() will free it, now
> > > conditionally on DEBUGFS_FSDATA_IS_REAL_FOPS_BIT, but that's not
> > > set for the function pointer in automount. As a result, removing
> > > an automount dentry would attempt to free the function pointer.
> > > Luckily, the only user of this (tracing) never removes it.
> > > 
> > > Nevertheless, it's safer if we just handle the fsdata in one way,
> > > namely either DEBUGFS_FSDATA_IS_REAL_FOPS_BIT or allocated. Thus,
> > > change the automount to allocate it, and use the real_fops in the
> > > data to indicate whether or not automount is filled, rather than
> > > adding a type tag. At least for now this isn't actually needed,
> > > but the next changes will require it.
> > > 
> > > Also check in debugfs_file_get() that it gets only called
> > > on regular files, just to make things clearer.
> > > 
> > > Signed-off-by: Johannes Berg <johannes.berg@intel.com>
> > > ---
> > > v2: add missing kfree() pointed out by smatch
> > 
> > Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> 
> I have to fix the Kconfig issue in one of the later (wireless) patches,
> but does that mean you'd actually prefer the debugfs changes go through
> the wireless tree, together with the code using it?

I'm all for you taking these through the wireless tree, have fun!

greg k-h

[PATCH v2 2/6] debugfs: annotate debugfs handlers vs. removal with lockdep

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

When you take a lock in a debugfs handler but also try
to remove the debugfs file under that lock, things can
deadlock since the removal has to wait for all users
to finish.

Add lockdep annotations in debugfs_file_get()/_put()
to catch such issues.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 fs/debugfs/file.c     | 10 ++++++++++
 fs/debugfs/inode.c    | 12 ++++++++++++
 fs/debugfs/internal.h |  6 ++++++
 3 files changed, 28 insertions(+)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index e00189aebbf4..3eff92450fd5 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -108,6 +108,12 @@ int debugfs_file_get(struct dentry *dentry)
 			kfree(fsd);
 			fsd = READ_ONCE(dentry->d_fsdata);
 		}
+#ifdef CONFIG_LOCKDEP
+		fsd->lock_name = kasprintf(GFP_KERNEL, "debugfs:%pd", dentry);
+		lockdep_register_key(&fsd->key);
+		lockdep_init_map(&fsd->lockdep_map, fsd->lock_name ?: "debugfs",
+				 &fsd->key, 0);
+#endif
 	}
 
 	/*
@@ -124,6 +130,8 @@ int debugfs_file_get(struct dentry *dentry)
 	if (!refcount_inc_not_zero(&fsd->active_users))
 		return -EIO;
 
+	lock_map_acquire_read(&fsd->lockdep_map);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(debugfs_file_get);
@@ -141,6 +149,8 @@ void debugfs_file_put(struct dentry *dentry)
 {
 	struct debugfs_fsdata *fsd = READ_ONCE(dentry->d_fsdata);
 
+	lock_map_release(&fsd->lockdep_map);
+
 	if (refcount_dec_and_test(&fsd->active_users))
 		complete(&fsd->active_users_drained);
 }
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index dcde4199a625..80f4f000dcc1 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -241,6 +241,14 @@ static void debugfs_release_dentry(struct dentry *dentry)
 	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
 		return;
 
+	/* check it wasn't a dir (no fsdata) or automount (no real_fops) */
+	if (fsd && fsd->real_fops) {
+#ifdef CONFIG_LOCKDEP
+		lockdep_unregister_key(&fsd->key);
+		kfree(fsd->lock_name);
+#endif
+	}
+
 	kfree(fsd);
 }
 
@@ -744,6 +752,10 @@ static void __debugfs_file_removed(struct dentry *dentry)
 	fsd = READ_ONCE(dentry->d_fsdata);
 	if ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)
 		return;
+
+	lock_map_acquire(&fsd->lockdep_map);
+	lock_map_release(&fsd->lockdep_map);
+
 	if (!refcount_dec_and_test(&fsd->active_users))
 		wait_for_completion(&fsd->active_users_drained);
 }
diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h
index f7c489b5a368..c7d61cfc97d2 100644
--- a/fs/debugfs/internal.h
+++ b/fs/debugfs/internal.h
@@ -7,6 +7,7 @@
 
 #ifndef _DEBUGFS_INTERNAL_H_
 #define _DEBUGFS_INTERNAL_H_
+#include <linux/lockdep.h>
 
 struct file_operations;
 
@@ -23,6 +24,11 @@ struct debugfs_fsdata {
 		struct {
 			refcount_t active_users;
 			struct completion active_users_drained;
+#ifdef CONFIG_LOCKDEP
+			struct lockdep_map lockdep_map;
+			struct lock_class_key key;
+			char *lock_name;
+#endif
 		};
 	};
 };
-- 
2.42.0

Re: [PATCH v2 2/6] debugfs: annotate debugfs handlers vs. removal with lockdep

[Greg Kroah-Hartman]

On Fri, Nov 24, 2023 at 05:25:25PM +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
> 
> When you take a lock in a debugfs handler but also try
> to remove the debugfs file under that lock, things can
> deadlock since the removal has to wait for all users
> to finish.
> 
> Add lockdep annotations in debugfs_file_get()/_put()
> to catch such issues.
> 
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[PATCH v2 3/6] debugfs: add API to allow debugfs operations cancellation

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

In some cases there might be longer-running hardware accesses
in debugfs files, or attempts to acquire locks, and we want
to still be able to quickly remove the files.

Introduce a cancellations API to use inside the debugfs handler
functions to be able to cancel such operations on a per-file
basis.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
v2:
 - use mutex to protect the cancellations and hold it around
   calling the cancel function so that cannot race with the
   handler finishing and leaving the cancellation.
---
 fs/debugfs/file.c       | 82 +++++++++++++++++++++++++++++++++++++++++
 fs/debugfs/inode.c      | 32 +++++++++++++++-
 fs/debugfs/internal.h   |  5 +++
 include/linux/debugfs.h | 19 ++++++++++
 4 files changed, 137 insertions(+), 1 deletion(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 3eff92450fd5..5568cdea3490 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -114,6 +114,8 @@ int debugfs_file_get(struct dentry *dentry)
 		lockdep_init_map(&fsd->lockdep_map, fsd->lock_name ?: "debugfs",
 				 &fsd->key, 0);
 #endif
+		INIT_LIST_HEAD(&fsd->cancellations);
+		mutex_init(&fsd->cancellations_mtx);
 	}
 
 	/*
@@ -156,6 +158,86 @@ void debugfs_file_put(struct dentry *dentry)
 }
 EXPORT_SYMBOL_GPL(debugfs_file_put);
 
+/**
+ * debugfs_enter_cancellation - enter a debugfs cancellation
+ * @file: the file being accessed
+ * @cancellation: the cancellation object, the cancel callback
+ *	inside of it must be initialized
+ *
+ * When a debugfs file is removed it needs to wait for all active
+ * operations to complete. However, the operation itself may need
+ * to wait for hardware or completion of some asynchronous process
+ * or similar. As such, it may need to be cancelled to avoid long
+ * waits or even deadlocks.
+ *
+ * This function can be used inside a debugfs handler that may
+ * need to be cancelled. As soon as this function is called, the
+ * cancellation's 'cancel' callback may be called, at which point
+ * the caller should proceed to call debugfs_leave_cancellation()
+ * and leave the debugfs handler function as soon as possible.
+ * Note that the 'cancel' callback is only ever called in the
+ * context of some kind of debugfs_remove().
+ *
+ * This function must be paired with debugfs_leave_cancellation().
+ */
+void debugfs_enter_cancellation(struct file *file,
+				struct debugfs_cancellation *cancellation)
+{
+	struct debugfs_fsdata *fsd;
+	struct dentry *dentry = F_DENTRY(file);
+
+	INIT_LIST_HEAD(&cancellation->list);
+
+	if (WARN_ON(!d_is_reg(dentry)))
+		return;
+
+	if (WARN_ON(!cancellation->cancel))
+		return;
+
+	fsd = READ_ONCE(dentry->d_fsdata);
+	if (WARN_ON(!fsd ||
+		    ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)))
+		return;
+
+	mutex_lock(&fsd->cancellations_mtx);
+	list_add(&cancellation->list, &fsd->cancellations);
+	mutex_unlock(&fsd->cancellations_mtx);
+
+	/* if we're already removing wake it up to cancel */
+	if (d_unlinked(dentry))
+		complete(&fsd->active_users_drained);
+}
+EXPORT_SYMBOL_GPL(debugfs_enter_cancellation);
+
+/**
+ * debugfs_leave_cancellation - leave cancellation section
+ * @file: the file being accessed
+ * @cancellation: the cancellation previously registered with
+ *	debugfs_enter_cancellation()
+ *
+ * See the documentation of debugfs_enter_cancellation().
+ */
+void debugfs_leave_cancellation(struct file *file,
+				struct debugfs_cancellation *cancellation)
+{
+	struct debugfs_fsdata *fsd;
+	struct dentry *dentry = F_DENTRY(file);
+
+	if (WARN_ON(!d_is_reg(dentry)))
+		return;
+
+	fsd = READ_ONCE(dentry->d_fsdata);
+	if (WARN_ON(!fsd ||
+		    ((unsigned long)fsd & DEBUGFS_FSDATA_IS_REAL_FOPS_BIT)))
+		return;
+
+	mutex_lock(&fsd->cancellations_mtx);
+	if (!list_empty(&cancellation->list))
+		list_del(&cancellation->list);
+	mutex_unlock(&fsd->cancellations_mtx);
+}
+EXPORT_SYMBOL_GPL(debugfs_leave_cancellation);
+
 /*
  * Only permit access to world-readable files when the kernel is locked down.
  * We also need to exclude any file that has ways to write or alter it as root
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 80f4f000dcc1..d53c2860b03c 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -247,6 +247,8 @@ static void debugfs_release_dentry(struct dentry *dentry)
 		lockdep_unregister_key(&fsd->key);
 		kfree(fsd->lock_name);
 #endif
+		WARN_ON(!list_empty(&fsd->cancellations));
+		mutex_destroy(&fsd->cancellations_mtx);
 	}
 
 	kfree(fsd);
@@ -756,8 +758,36 @@ static void __debugfs_file_removed(struct dentry *dentry)
 	lock_map_acquire(&fsd->lockdep_map);
 	lock_map_release(&fsd->lockdep_map);
 
-	if (!refcount_dec_and_test(&fsd->active_users))
+	/* if we hit zero, just wait for all to finish */
+	if (!refcount_dec_and_test(&fsd->active_users)) {
 		wait_for_completion(&fsd->active_users_drained);
+		return;
+	}
+
+	/* if we didn't hit zero, try to cancel any we can */
+	while (refcount_read(&fsd->active_users)) {
+		struct debugfs_cancellation *c;
+
+		/*
+		 * Lock the cancellations. Note that the cancellations
+		 * structs are meant to be on the stack, so we need to
+		 * ensure we either use them here or don't touch them,
+		 * and debugfs_leave_cancellation() will wait for this
+		 * to be finished processing before exiting one. It may
+		 * of course win and remove the cancellation, but then
+		 * chances are we never even got into this bit, we only
+		 * do if the refcount isn't zero already.
+		 */
+		mutex_lock(&fsd->cancellations_mtx);
+		while ((c = list_first_entry_or_null(&fsd->cancellations,
+						     typeof(*c), list))) {
+			list_del_init(&c->list);
+			c->cancel(dentry, c->cancel_data);
+		}
+		mutex_unlock(&fsd->cancellations_mtx);
+
+		wait_for_completion(&fsd->active_users_drained);
+	}
 }
 
 static void remove_one(struct dentry *victim)
diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h
index c7d61cfc97d2..0c4c68cf161f 100644
--- a/fs/debugfs/internal.h
+++ b/fs/debugfs/internal.h
@@ -8,6 +8,7 @@
 #ifndef _DEBUGFS_INTERNAL_H_
 #define _DEBUGFS_INTERNAL_H_
 #include <linux/lockdep.h>
+#include <linux/list.h>
 
 struct file_operations;
 
@@ -29,6 +30,10 @@ struct debugfs_fsdata {
 			struct lock_class_key key;
 			char *lock_name;
 #endif
+
+			/* protect cancellations */
+			struct mutex cancellations_mtx;
+			struct list_head cancellations;
 		};
 	};
 };
diff --git a/include/linux/debugfs.h b/include/linux/debugfs.h
index ea2d919fd9c7..c9c65b132c0f 100644
--- a/include/linux/debugfs.h
+++ b/include/linux/debugfs.h
@@ -171,6 +171,25 @@ ssize_t debugfs_write_file_bool(struct file *file, const char __user *user_buf,
 ssize_t debugfs_read_file_str(struct file *file, char __user *user_buf,
 			      size_t count, loff_t *ppos);
 
+/**
+ * struct debugfs_cancellation - cancellation data
+ * @list: internal, for keeping track
+ * @cancel: callback to call
+ * @cancel_data: extra data for the callback to call
+ */
+struct debugfs_cancellation {
+	struct list_head list;
+	void (*cancel)(struct dentry *, void *);
+	void *cancel_data;
+};
+
+void __acquires(cancellation)
+debugfs_enter_cancellation(struct file *file,
+			   struct debugfs_cancellation *cancellation);
+void __releases(cancellation)
+debugfs_leave_cancellation(struct file *file,
+			   struct debugfs_cancellation *cancellation);
+
 #else
 
 #include <linux/err.h>
-- 
2.42.0

Re: [PATCH v2 3/6] debugfs: add API to allow debugfs operations cancellation

[Greg Kroah-Hartman]

On Fri, Nov 24, 2023 at 05:25:26PM +0100, Johannes Berg wrote:
> From: Johannes Berg <johannes.berg@intel.com>
> 
> In some cases there might be longer-running hardware accesses
> in debugfs files, or attempts to acquire locks, and we want
> to still be able to quickly remove the files.
> 
> Introduce a cancellations API to use inside the debugfs handler
> functions to be able to cancel such operations on a per-file
> basis.
> 
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

[PATCH v2 4/6] wifi: cfg80211: add locked debugfs wrappers

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

Add wrappers for debugfs files that should be called with
the wiphy mutex held, while the file is also to be removed
under the wiphy mutex. This could otherwise deadlock when
a file is trying to acquire the wiphy mutex while the code
removing it holds the mutex but waits for the removal.

This actually works by pushing the execution of the read
or write handler to a wiphy work that can be cancelled
using the debugfs cancellation API.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 include/net/cfg80211.h |  46 ++++++++++++
 net/wireless/debugfs.c | 160 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 206 insertions(+)

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index b137a33a1b68..4ecfb06c413d 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -9299,4 +9299,50 @@ bool cfg80211_valid_disable_subchannel_bitmap(u16 *bitmap,
  */
 void cfg80211_links_removed(struct net_device *dev, u16 link_mask);
 
+#ifdef CONFIG_CFG80211_DEBUGFS
+/**
+ * wiphy_locked_debugfs_read - do a locked read in debugfs
+ * @wiphy: the wiphy to use
+ * @file: the file being read
+ * @buf: the buffer to fill and then read from
+ * @bufsize: size of the buffer
+ * @userbuf: the user buffer to copy to
+ * @count: read count
+ * @ppos: read position
+ * @handler: the read handler to call (under wiphy lock)
+ * @data: additional data to pass to the read handler
+ */
+ssize_t wiphy_locked_debugfs_read(struct wiphy *wiphy, struct file *file,
+				  char *buf, size_t bufsize,
+				  char __user *userbuf, size_t count,
+				  loff_t *ppos,
+				  ssize_t (*handler)(struct wiphy *wiphy,
+						     struct file *file,
+						     char *buf,
+						     size_t bufsize,
+						     void *data),
+				  void *data);
+
+/**
+ * wiphy_locked_debugfs_write - do a locked write in debugfs
+ * @wiphy: the wiphy to use
+ * @file: the file being written to
+ * @buf: the buffer to copy the user data to
+ * @bufsize: size of the buffer
+ * @userbuf: the user buffer to copy from
+ * @count: read count
+ * @handler: the write handler to call (under wiphy lock)
+ * @data: additional data to pass to the write handler
+ */
+ssize_t wiphy_locked_debugfs_write(struct wiphy *wiphy, struct file *file,
+				   char *buf, size_t bufsize,
+				   const char __user *userbuf, size_t count,
+				   ssize_t (*handler)(struct wiphy *wiphy,
+						      struct file *file,
+						      char *buf,
+						      size_t count,
+						      void *data),
+				   void *data);
+#endif
+
 #endif /* __NET_CFG80211_H */
diff --git a/net/wireless/debugfs.c b/net/wireless/debugfs.c
index 0878b162890a..40e49074e2ee 100644
--- a/net/wireless/debugfs.c
+++ b/net/wireless/debugfs.c
@@ -4,6 +4,7 @@
  *
  * Copyright 2009	Luis R. Rodriguez <lrodriguez@atheros.com>
  * Copyright 2007	Johannes Berg <johannes@sipsolutions.net>
+ * Copyright (C) 2023 Intel Corporation
  */
 
 #include <linux/slab.h>
@@ -109,3 +110,162 @@ void cfg80211_debugfs_rdev_add(struct cfg80211_registered_device *rdev)
 	DEBUGFS_ADD(long_retry_limit);
 	DEBUGFS_ADD(ht40allow_map);
 }
+
+struct debugfs_read_work {
+	struct wiphy_work work;
+	ssize_t (*handler)(struct wiphy *wiphy,
+			   struct file *file,
+			   char *buf,
+			   size_t count,
+			   void *data);
+	struct wiphy *wiphy;
+	struct file *file;
+	char *buf;
+	size_t bufsize;
+	void *data;
+	ssize_t ret;
+	struct completion completion;
+};
+
+static void wiphy_locked_debugfs_read_work(struct wiphy *wiphy,
+					   struct wiphy_work *work)
+{
+	struct debugfs_read_work *w = container_of(work, typeof(*w), work);
+
+	w->ret = w->handler(w->wiphy, w->file, w->buf, w->bufsize, w->data);
+	complete(&w->completion);
+}
+
+static void wiphy_locked_debugfs_read_cancel(struct dentry *dentry,
+					     void *data)
+{
+	struct debugfs_read_work *w = data;
+
+	wiphy_work_cancel(w->wiphy, &w->work);
+	complete(&w->completion);
+}
+
+ssize_t wiphy_locked_debugfs_read(struct wiphy *wiphy, struct file *file,
+				  char *buf, size_t bufsize,
+				  char __user *userbuf, size_t count,
+				  loff_t *ppos,
+				  ssize_t (*handler)(struct wiphy *wiphy,
+						     struct file *file,
+						     char *buf,
+						     size_t bufsize,
+						     void *data),
+				  void *data)
+{
+	struct debugfs_read_work work = {
+		.handler = handler,
+		.wiphy = wiphy,
+		.file = file,
+		.buf = buf,
+		.bufsize = bufsize,
+		.data = data,
+		.ret = -ENODEV,
+		.completion = COMPLETION_INITIALIZER_ONSTACK(work.completion),
+	};
+	struct debugfs_cancellation cancellation = {
+		.cancel = wiphy_locked_debugfs_read_cancel,
+		.cancel_data = &work,
+	};
+
+	/* don't leak stack data or whatever */
+	memset(buf, 0, bufsize);
+
+	wiphy_work_init(&work.work, wiphy_locked_debugfs_read_work);
+	wiphy_work_queue(wiphy, &work.work);
+
+	debugfs_enter_cancellation(file, &cancellation);
+	wait_for_completion(&work.completion);
+	debugfs_leave_cancellation(file, &cancellation);
+
+	if (work.ret < 0)
+		return work.ret;
+
+	if (WARN_ON(work.ret > bufsize))
+		return -EINVAL;
+
+	return simple_read_from_buffer(userbuf, count, ppos, buf, work.ret);
+}
+EXPORT_SYMBOL_GPL(wiphy_locked_debugfs_read);
+
+struct debugfs_write_work {
+	struct wiphy_work work;
+	ssize_t (*handler)(struct wiphy *wiphy,
+			   struct file *file,
+			   char *buf,
+			   size_t count,
+			   void *data);
+	struct wiphy *wiphy;
+	struct file *file;
+	char *buf;
+	size_t count;
+	void *data;
+	ssize_t ret;
+	struct completion completion;
+};
+
+static void wiphy_locked_debugfs_write_work(struct wiphy *wiphy,
+					    struct wiphy_work *work)
+{
+	struct debugfs_write_work *w = container_of(work, typeof(*w), work);
+
+	w->ret = w->handler(w->wiphy, w->file, w->buf, w->count, w->data);
+	complete(&w->completion);
+}
+
+static void wiphy_locked_debugfs_write_cancel(struct dentry *dentry,
+					      void *data)
+{
+	struct debugfs_write_work *w = data;
+
+	wiphy_work_cancel(w->wiphy, &w->work);
+	complete(&w->completion);
+}
+
+ssize_t wiphy_locked_debugfs_write(struct wiphy *wiphy,
+				   struct file *file, char *buf, size_t bufsize,
+				   const char __user *userbuf, size_t count,
+				   ssize_t (*handler)(struct wiphy *wiphy,
+						      struct file *file,
+						      char *buf,
+						      size_t count,
+						      void *data),
+				   void *data)
+{
+	struct debugfs_write_work work = {
+		.handler = handler,
+		.wiphy = wiphy,
+		.file = file,
+		.buf = buf,
+		.count = count,
+		.data = data,
+		.ret = -ENODEV,
+		.completion = COMPLETION_INITIALIZER_ONSTACK(work.completion),
+	};
+	struct debugfs_cancellation cancellation = {
+		.cancel = wiphy_locked_debugfs_write_cancel,
+		.cancel_data = &work,
+	};
+
+	/* mostly used for strings so enforce NUL-termination for safety */
+	if (count >= bufsize)
+		return -EINVAL;
+
+	memset(buf, 0, bufsize);
+
+	if (copy_from_user(buf, userbuf, count))
+		return -EFAULT;
+
+	wiphy_work_init(&work.work, wiphy_locked_debugfs_write_work);
+	wiphy_work_queue(wiphy, &work.work);
+
+	debugfs_enter_cancellation(file, &cancellation);
+	wait_for_completion(&work.completion);
+	debugfs_leave_cancellation(file, &cancellation);
+
+	return work.ret;
+}
+EXPORT_SYMBOL_GPL(wiphy_locked_debugfs_write);
-- 
2.42.0

[PATCH v2 5/6] wifi: mac80211: use wiphy locked debugfs helpers for agg_status

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

The read is currently with RCU and the write can deadlock,
convert both for the sake of illustration.

Make mac80211 depend on cfg80211 debugfs to get the helpers,
but mac80211 debugfs without it does nothing anyway.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
v2:
 - make mac80211 debugfs depend on cfg80211 debugfs, it's
   anyway useless without it
---
 net/mac80211/Kconfig       |  2 +-
 net/mac80211/debugfs_sta.c | 74 +++++++++++++++++++++-----------------
 2 files changed, 43 insertions(+), 33 deletions(-)

diff --git a/net/mac80211/Kconfig b/net/mac80211/Kconfig
index 037ab74f5ade..cb0291decf2e 100644
--- a/net/mac80211/Kconfig
+++ b/net/mac80211/Kconfig
@@ -88,7 +88,7 @@ config MAC80211_LEDS
 
 config MAC80211_DEBUGFS
 	bool "Export mac80211 internals in DebugFS"
-	depends on MAC80211 && DEBUG_FS
+	depends on MAC80211 && CFG80211_DEBUGFS
 	help
 	  Select this to see extensive information about
 	  the internal state of mac80211 in debugfs.
diff --git a/net/mac80211/debugfs_sta.c b/net/mac80211/debugfs_sta.c
index 06e3613bf46b..5bf507ebb096 100644
--- a/net/mac80211/debugfs_sta.c
+++ b/net/mac80211/debugfs_sta.c
@@ -312,23 +312,14 @@ static ssize_t sta_aql_write(struct file *file, const char __user *userbuf,
 STA_OPS_RW(aql);
 
 
-static ssize_t sta_agg_status_read(struct file *file, char __user *userbuf,
-					size_t count, loff_t *ppos)
+static ssize_t sta_agg_status_do_read(struct wiphy *wiphy, struct file *file,
+				      char *buf, size_t bufsz, void *data)
 {
-	char *buf, *p;
-	ssize_t bufsz = 71 + IEEE80211_NUM_TIDS * 40;
+	struct sta_info *sta = data;
+	char *p = buf;
 	int i;
-	struct sta_info *sta = file->private_data;
 	struct tid_ampdu_rx *tid_rx;
 	struct tid_ampdu_tx *tid_tx;
-	ssize_t ret;
-
-	buf = kzalloc(bufsz, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-	p = buf;
-
-	rcu_read_lock();
 
 	p += scnprintf(p, bufsz + buf - p, "next dialog_token: %#02x\n",
 			sta->ampdu_mlme.dialog_token_allocator + 1);
@@ -338,8 +329,8 @@ static ssize_t sta_agg_status_read(struct file *file, char __user *userbuf,
 	for (i = 0; i < IEEE80211_NUM_TIDS; i++) {
 		bool tid_rx_valid;
 
-		tid_rx = rcu_dereference(sta->ampdu_mlme.tid_rx[i]);
-		tid_tx = rcu_dereference(sta->ampdu_mlme.tid_tx[i]);
+		tid_rx = wiphy_dereference(wiphy, sta->ampdu_mlme.tid_rx[i]);
+		tid_tx = wiphy_dereference(wiphy, sta->ampdu_mlme.tid_tx[i]);
 		tid_rx_valid = test_bit(i, sta->ampdu_mlme.agg_session_valid);
 
 		p += scnprintf(p, bufsz + buf - p, "%02d", i);
@@ -358,31 +349,39 @@ static ssize_t sta_agg_status_read(struct file *file, char __user *userbuf,
 				tid_tx ? skb_queue_len(&tid_tx->pending) : 0);
 		p += scnprintf(p, bufsz + buf - p, "\n");
 	}
-	rcu_read_unlock();
 
-	ret = simple_read_from_buffer(userbuf, count, ppos, buf, p - buf);
+	return p - buf;
+}
+
+static ssize_t sta_agg_status_read(struct file *file, char __user *userbuf,
+				   size_t count, loff_t *ppos)
+{
+	struct sta_info *sta = file->private_data;
+	struct wiphy *wiphy = sta->local->hw.wiphy;
+	size_t bufsz = 71 + IEEE80211_NUM_TIDS * 40;
+	char *buf = kmalloc(bufsz, GFP_KERNEL);
+	ssize_t ret;
+
+	if (!buf)
+		return -ENOMEM;
+
+	ret = wiphy_locked_debugfs_read(wiphy, file, buf, bufsz,
+					userbuf, count, ppos,
+					sta_agg_status_do_read, sta);
 	kfree(buf);
+
 	return ret;
 }
 
-static ssize_t sta_agg_status_write(struct file *file, const char __user *userbuf,
-				    size_t count, loff_t *ppos)
+static ssize_t sta_agg_status_do_write(struct wiphy *wiphy, struct file *file,
+				       char *buf, size_t count, void *data)
 {
-	char _buf[25] = {}, *buf = _buf;
-	struct sta_info *sta = file->private_data;
+	struct sta_info *sta = data;
 	bool start, tx;
 	unsigned long tid;
-	char *pos;
+	char *pos = buf;
 	int ret, timeout = 5000;
 
-	if (count > sizeof(_buf))
-		return -EINVAL;
-
-	if (copy_from_user(buf, userbuf, count))
-		return -EFAULT;
-
-	buf[sizeof(_buf) - 1] = '\0';
-	pos = buf;
 	buf = strsep(&pos, " ");
 	if (!buf)
 		return -EINVAL;
@@ -420,7 +419,6 @@ static ssize_t sta_agg_status_write(struct file *file, const char __user *userbu
 	if (ret || tid >= IEEE80211_NUM_TIDS)
 		return -EINVAL;
 
-	wiphy_lock(sta->local->hw.wiphy);
 	if (tx) {
 		if (start)
 			ret = ieee80211_start_tx_ba_session(&sta->sta, tid,
@@ -432,10 +430,22 @@ static ssize_t sta_agg_status_write(struct file *file, const char __user *userbu
 					       3, true);
 		ret = 0;
 	}
-	wiphy_unlock(sta->local->hw.wiphy);
 
 	return ret ?: count;
 }
+
+static ssize_t sta_agg_status_write(struct file *file,
+				    const char __user *userbuf,
+				    size_t count, loff_t *ppos)
+{
+	struct sta_info *sta = file->private_data;
+	struct wiphy *wiphy = sta->local->hw.wiphy;
+	char _buf[26];
+
+	return wiphy_locked_debugfs_write(wiphy, file, _buf, sizeof(_buf),
+					  userbuf, count,
+					  sta_agg_status_do_write, sta);
+}
 STA_OPS_RW(agg_status);
 
 /* link sta attributes */
-- 
2.42.0

[PATCH v2 6/6] wifi: mac80211: use wiphy locked debugfs for sdata/link

[Johannes Berg]

From: Johannes Berg <johannes.berg@intel.com>

The debugfs files for netdevs (sdata) and links are removed
with the wiphy mutex held, which may deadlock. Use the new
wiphy locked debugfs to avoid that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
---
 net/mac80211/debugfs_netdev.c | 150 ++++++++++++++++++++++++----------
 1 file changed, 105 insertions(+), 45 deletions(-)

diff --git a/net/mac80211/debugfs_netdev.c b/net/mac80211/debugfs_netdev.c
index ec91e131b29e..80aeb25f1b68 100644
--- a/net/mac80211/debugfs_netdev.c
+++ b/net/mac80211/debugfs_netdev.c
@@ -22,88 +22,148 @@
 #include "debugfs_netdev.h"
 #include "driver-ops.h"
 
+struct ieee80211_if_read_sdata_data {
+	ssize_t (*format)(const struct ieee80211_sub_if_data *, char *, int);
+	struct ieee80211_sub_if_data *sdata;
+};
+
+static ssize_t ieee80211_if_read_sdata_handler(struct wiphy *wiphy,
+					       struct file *file,
+					       char *buf,
+					       size_t bufsize,
+					       void *data)
+{
+	struct ieee80211_if_read_sdata_data *d = data;
+
+	return d->format(d->sdata, buf, bufsize);
+}
+
 static ssize_t ieee80211_if_read_sdata(
-	struct ieee80211_sub_if_data *sdata,
+	struct file *file,
 	char __user *userbuf,
 	size_t count, loff_t *ppos,
 	ssize_t (*format)(const struct ieee80211_sub_if_data *sdata, char *, int))
 {
+	struct ieee80211_sub_if_data *sdata = file->private_data;
+	struct ieee80211_if_read_sdata_data data = {
+		.format = format,
+		.sdata = sdata,
+	};
 	char buf[200];
-	ssize_t ret = -EINVAL;
 
-	wiphy_lock(sdata->local->hw.wiphy);
-	ret = (*format)(sdata, buf, sizeof(buf));
-	wiphy_unlock(sdata->local->hw.wiphy);
+	return wiphy_locked_debugfs_read(sdata->local->hw.wiphy,
+					 file, buf, sizeof(buf),
+					 userbuf, count, ppos,
+					 ieee80211_if_read_sdata_handler,
+					 &data);
+}
 
-	if (ret >= 0)
-		ret = simple_read_from_buffer(userbuf, count, ppos, buf, ret);
+struct ieee80211_if_write_sdata_data {
+	ssize_t (*write)(struct ieee80211_sub_if_data *, const char *, int);
+	struct ieee80211_sub_if_data *sdata;
+};
 
-	return ret;
+static ssize_t ieee80211_if_write_sdata_handler(struct wiphy *wiphy,
+						struct file *file,
+						char *buf,
+						size_t count,
+						void *data)
+{
+	struct ieee80211_if_write_sdata_data *d = data;
+
+	return d->write(d->sdata, buf, count);
 }
 
 static ssize_t ieee80211_if_write_sdata(
-	struct ieee80211_sub_if_data *sdata,
+	struct file *file,
 	const char __user *userbuf,
 	size_t count, loff_t *ppos,
 	ssize_t (*write)(struct ieee80211_sub_if_data *sdata, const char *, int))
 {
+	struct ieee80211_sub_if_data *sdata = file->private_data;
+	struct ieee80211_if_write_sdata_data data = {
+		.write = write,
+		.sdata = sdata,
+	};
 	char buf[64];
-	ssize_t ret;
 
-	if (count >= sizeof(buf))
-		return -E2BIG;
+	return wiphy_locked_debugfs_write(sdata->local->hw.wiphy,
+					  file, buf, sizeof(buf),
+					  userbuf, count,
+					  ieee80211_if_write_sdata_handler,
+					  &data);
+}
 
-	if (copy_from_user(buf, userbuf, count))
-		return -EFAULT;
-	buf[count] = '\0';
+struct ieee80211_if_read_link_data {
+	ssize_t (*format)(const struct ieee80211_link_data *, char *, int);
+	struct ieee80211_link_data *link;
+};
 
-	wiphy_lock(sdata->local->hw.wiphy);
-	ret = (*write)(sdata, buf, count);
-	wiphy_unlock(sdata->local->hw.wiphy);
+static ssize_t ieee80211_if_read_link_handler(struct wiphy *wiphy,
+					      struct file *file,
+					      char *buf,
+					      size_t bufsize,
+					      void *data)
+{
+	struct ieee80211_if_read_link_data *d = data;
 
-	return ret;
+	return d->format(d->link, buf, bufsize);
 }
 
 static ssize_t ieee80211_if_read_link(
-	struct ieee80211_link_data *link,
+	struct file *file,
 	char __user *userbuf,
 	size_t count, loff_t *ppos,
 	ssize_t (*format)(const struct ieee80211_link_data *link, char *, int))
 {
+	struct ieee80211_link_data *link = file->private_data;
+	struct ieee80211_if_read_link_data data = {
+		.format = format,
+		.link = link,
+	};
 	char buf[200];
-	ssize_t ret = -EINVAL;
 
-	wiphy_lock(link->sdata->local->hw.wiphy);
-	ret = (*format)(link, buf, sizeof(buf));
-	wiphy_unlock(link->sdata->local->hw.wiphy);
+	return wiphy_locked_debugfs_read(link->sdata->local->hw.wiphy,
+					 file, buf, sizeof(buf),
+					 userbuf, count, ppos,
+					 ieee80211_if_read_link_handler,
+					 &data);
+}
 
-	if (ret >= 0)
-		ret = simple_read_from_buffer(userbuf, count, ppos, buf, ret);
+struct ieee80211_if_write_link_data {
+	ssize_t (*write)(struct ieee80211_link_data *, const char *, int);
+	struct ieee80211_link_data *link;
+};
 
-	return ret;
+static ssize_t ieee80211_if_write_link_handler(struct wiphy *wiphy,
+					       struct file *file,
+					       char *buf,
+					       size_t count,
+					       void *data)
+{
+	struct ieee80211_if_write_sdata_data *d = data;
+
+	return d->write(d->sdata, buf, count);
 }
 
 static ssize_t ieee80211_if_write_link(
-	struct ieee80211_link_data *link,
+	struct file *file,
 	const char __user *userbuf,
 	size_t count, loff_t *ppos,
 	ssize_t (*write)(struct ieee80211_link_data *link, const char *, int))
 {
+	struct ieee80211_link_data *link = file->private_data;
+	struct ieee80211_if_write_link_data data = {
+		.write = write,
+		.link = link,
+	};
 	char buf[64];
-	ssize_t ret;
 
-	if (count >= sizeof(buf))
-		return -E2BIG;
-
-	if (copy_from_user(buf, userbuf, count))
-		return -EFAULT;
-	buf[count] = '\0';
-
-	wiphy_lock(link->sdata->local->hw.wiphy);
-	ret = (*write)(link, buf, count);
-	wiphy_unlock(link->sdata->local->hw.wiphy);
-
-	return ret;
+	return wiphy_locked_debugfs_write(link->sdata->local->hw.wiphy,
+					  file, buf, sizeof(buf),
+					  userbuf, count,
+					  ieee80211_if_write_link_handler,
+					  &data);
 }
 
 #define IEEE80211_IF_FMT(name, type, field, format_string)		\
@@ -173,7 +233,7 @@ static ssize_t ieee80211_if_read_##name(struct file *file,		\
 					char __user *userbuf,		\
 					size_t count, loff_t *ppos)	\
 {									\
-	return ieee80211_if_read_sdata(file->private_data,		\
+	return ieee80211_if_read_sdata(file,				\
 				       userbuf, count, ppos,		\
 				       ieee80211_if_fmt_##name);	\
 }
@@ -183,7 +243,7 @@ static ssize_t ieee80211_if_write_##name(struct file *file,		\
 					 const char __user *userbuf,	\
 					 size_t count, loff_t *ppos)	\
 {									\
-	return ieee80211_if_write_sdata(file->private_data, userbuf,	\
+	return ieee80211_if_write_sdata(file, userbuf,			\
 					count, ppos,			\
 					ieee80211_if_parse_##name);	\
 }
@@ -211,7 +271,7 @@ static ssize_t ieee80211_if_read_##name(struct file *file,		\
 					char __user *userbuf,		\
 					size_t count, loff_t *ppos)	\
 {									\
-	return ieee80211_if_read_link(file->private_data,		\
+	return ieee80211_if_read_link(file,				\
 				      userbuf, count, ppos,		\
 				      ieee80211_if_fmt_##name);	\
 }
@@ -221,7 +281,7 @@ static ssize_t ieee80211_if_write_##name(struct file *file,		\
 					 const char __user *userbuf,	\
 					 size_t count, loff_t *ppos)	\
 {									\
-	return ieee80211_if_write_link(file->private_data, userbuf,	\
+	return ieee80211_if_write_link(file, userbuf,			\
 				       count, ppos,			\
 				       ieee80211_if_parse_##name);	\
 }
-- 
2.42.0

Re: [PATCH v2 0/6] fixes for debugfs/wireless locking issue

[Ben Greear]

On 11/24/23 08:25, Johannes Berg wrote:
> There's a locking issue in wireless where it takes a lock inside
> a debugfs file handler that's also taken around the removal of
> the debugfs file, and this causes a deadlock due to the proxy
> object use. Fixing the debugfs removal is tricky because some
> of the objects represented there fundamentally are deleted with
> the lock held. Not taking the lock in the debugfs file is also
> not really the right thing to do. Therefore, right now, the only
> way to fix this would be to not have the debugfs files entirely,
> but that isn't really helpful either.

I have been running the RFC series and haven't noticed problems, so you
can add:

Tested-by: Ben Greear <greearb@candelatech.com>

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com