[PATCH 5.15] kernfs: switch global kernfs_rwsem lock to per-fs lock

29 Nov 2024

From: Minchan Kim minchan@kernel.org
[ Upstream commit 393c3714081a53795bbff0e985d24146def6f57f ]
The kernfs implementation has big lock granularity(kernfs_rwsem) so
every kernfs-based(e.g., sysfs, cgroup) fs are able to compete the
lock. It makes trouble for some cases to wait the global lock
for a long time even though they are totally independent contexts
each other.
A general example is process A goes under direct reclaim with holding
the lock when it accessed the file in sysfs and process B is waiting
the lock with exclusive mode and then process C is waiting the lock
until process B could finish the job after it gets the lock from
process A.
This patch switches the global kernfs_rwsem to per-fs lock, which
put the rwsem into kernfs_root.
Suggested-by: Tejun Heo tj@kernel.org
Acked-by: Tejun Heo tj@kernel.org
Signed-off-by: Minchan Kim minchan@kernel.org
Link: https://lore.kernel.org/r/20211118230008.2679780-1-minchan@kernel.org
Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
Signed-off-by: Jeremi Piotrowski jpiotrowski@linux.microsoft.com
---
Hi Stable Maintainers,
This upstream commit fixes a kernel hang due to severe lock contention on
kernfs_rwsem that occurs when container workloads perform a lot of cgroupfs
accesses. Could you please apply to 5.15.y? I cherry-pick the upstream commit
to v5.15.173 and then performed `git format-patch`.
Thanks,
Jeremi
fs/kernfs/dir.c        | 110 ++++++++++++++++++++++++-----------------
 fs/kernfs/file.c       |   6 ++-
 fs/kernfs/inode.c      |  22 ++++++---
 fs/kernfs/mount.c      |  15 +++---
 fs/kernfs/symlink.c    |   5 +-
 include/linux/kernfs.h |   2 +
 6 files changed, 97 insertions(+), 63 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 36430bdf9381..ebe4ab0765ee 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -17,7 +17,6 @@
#include "kernfs-internal.h"
-DECLARE_RWSEM(kernfs_rwsem);
 static DEFINE_SPINLOCK(kernfs_rename_lock);	/* kn->parent and ->name */
 /*
  * Don't use rename_lock to piggy back on pr_cont_buf. We don't want to
@@ -34,7 +33,7 @@ static DEFINE_SPINLOCK(kernfs_idr_lock);	/* root->ino_idr */
static bool kernfs_active(struct kernfs_node *kn)
 {
-	lockdep_assert_held(&kernfs_rwsem);
+	lockdep_assert_held(&kernfs_root(kn)->kernfs_rwsem);
    return atomic_read(&kn->active) >= 0;
 }
@@ -465,14 +464,15 @@ void kernfs_put_active(struct kernfs_node *kn)
  * return after draining is complete.
  */
 static void kernfs_drain(struct kernfs_node *kn)
-	__releases(&kernfs_rwsem) __acquires(&kernfs_rwsem)
+	__releases(&kernfs_root(kn)->kernfs_rwsem)
+	__acquires(&kernfs_root(kn)->kernfs_rwsem)
 {
    struct kernfs_root *root = kernfs_root(kn);
-	lockdep_assert_held_write(&kernfs_rwsem);
+	lockdep_assert_held_write(&root->kernfs_rwsem);
    WARN_ON_ONCE(kernfs_active(kn));
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
if (kernfs_lockdep(kn)) {
    	rwsem_acquire(&kn->dep_map, 0, 0, _RET_IP_);
@@ -491,7 +491,7 @@ static void kernfs_drain(struct kernfs_node *kn)
kernfs_drain_open_files(kn);
-	down_write(&kernfs_rwsem);
+	down_write(&root->kernfs_rwsem);
 }
/**
@@ -740,11 +740,12 @@ struct kernfs_node *kernfs_find_and_get_node_by_id(struct kernfs_root *root,
 int kernfs_add_one(struct kernfs_node *kn)
 {
    struct kernfs_node *parent = kn->parent;
+	struct kernfs_root *root = kernfs_root(parent);
    struct kernfs_iattrs *ps_iattr;
    bool has_ns;
    int ret;
-	down_write(&kernfs_rwsem);
+	down_write(&root->kernfs_rwsem);
ret = -EINVAL;
    has_ns = kernfs_ns_enabled(parent);
@@ -775,7 +776,7 @@ int kernfs_add_one(struct kernfs_node *kn)
    	ps_iattr->ia_mtime = ps_iattr->ia_ctime;
    }
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
/*
     * Activate the new node unless CREATE_DEACTIVATED is requested.
@@ -789,7 +790,7 @@ int kernfs_add_one(struct kernfs_node *kn)
    return 0;
out_unlock:
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
    return ret;
 }
@@ -810,7 +811,7 @@ static struct kernfs_node *kernfs_find_ns(struct kernfs_node *parent,
    bool has_ns = kernfs_ns_enabled(parent);
    unsigned int hash;
-	lockdep_assert_held(&kernfs_rwsem);
+	lockdep_assert_held(&kernfs_root(parent)->kernfs_rwsem);
if (has_ns != (bool)ns) {
    	WARN(1, KERN_WARNING "kernfs: ns %s in '%s' for '%s'\n",
@@ -842,7 +843,7 @@ static struct kernfs_node *kernfs_walk_ns(struct kernfs_node *parent,
    size_t len;
    char *p, *name;
-	lockdep_assert_held_read(&kernfs_rwsem);
+	lockdep_assert_held_read(&kernfs_root(parent)->kernfs_rwsem);
spin_lock_irq(&kernfs_pr_cont_lock);
@@ -880,11 +881,12 @@ struct kernfs_node *kernfs_find_and_get_ns(struct kernfs_node *parent,
    				   const char *name, const void *ns)
 {
    struct kernfs_node *kn;
+	struct kernfs_root *root = kernfs_root(parent);
-	down_read(&kernfs_rwsem);
+	down_read(&root->kernfs_rwsem);
    kn = kernfs_find_ns(parent, name, ns);
    kernfs_get(kn);
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
return kn;
 }
@@ -904,11 +906,12 @@ struct kernfs_node *kernfs_walk_and_get_ns(struct kernfs_node *parent,
    				   const char *path, const void *ns)
 {
    struct kernfs_node *kn;
+	struct kernfs_root *root = kernfs_root(parent);
-	down_read(&kernfs_rwsem);
+	down_read(&root->kernfs_rwsem);
    kn = kernfs_walk_ns(parent, path, ns);
    kernfs_get(kn);
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
return kn;
 }
@@ -933,6 +936,7 @@ struct kernfs_root *kernfs_create_root(struct kernfs_syscall_ops *scops,
    	return ERR_PTR(-ENOMEM);
idr_init(&root->ino_idr);
+	init_rwsem(&root->kernfs_rwsem);
    INIT_LIST_HEAD(&root->supers);
/*
@@ -1056,6 +1060,7 @@ struct kernfs_node *kernfs_create_empty_dir(struct kernfs_node *parent,
 static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
 {
    struct kernfs_node *kn;
+	struct kernfs_root *root;
if (flags & LOOKUP_RCU)
    	return -ECHILD;
@@ -1067,18 +1072,19 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
    	/* If the kernfs parent node has changed discard and
    	 * proceed to ->lookup.
    	 */
-		down_read(&kernfs_rwsem);
    	spin_lock(&dentry->d_lock);
    	parent = kernfs_dentry_node(dentry->d_parent);
    	if (parent) {
+			spin_unlock(&dentry->d_lock);
+			root = kernfs_root(parent);
+			down_read(&root->kernfs_rwsem);
    		if (kernfs_dir_changed(parent, dentry)) {
-				spin_unlock(&dentry->d_lock);
-				up_read(&kernfs_rwsem);
+				up_read(&root->kernfs_rwsem);
    			return 0;
    		}
-		}
-		spin_unlock(&dentry->d_lock);
-		up_read(&kernfs_rwsem);
+			up_read(&root->kernfs_rwsem);
+		} else
+			spin_unlock(&dentry->d_lock);
/* The kernfs parent node hasn't changed, leave the
    	 * dentry negative and return success.
@@ -1087,7 +1093,8 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
    }
kn = kernfs_dentry_node(dentry);
-	down_read(&kernfs_rwsem);
+	root = kernfs_root(kn);
+	down_read(&root->kernfs_rwsem);
/* The kernfs node has been deactivated */
    if (!kernfs_active(kn))
@@ -1106,10 +1113,10 @@ static int kernfs_dop_revalidate(struct dentry *dentry, unsigned int flags)
        kernfs_info(dentry->d_sb)->ns != kn->ns)
    	goto out_bad;
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
    return 1;
 out_bad:
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
    return 0;
 }
@@ -1123,10 +1130,12 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
 {
    struct kernfs_node *parent = dir->i_private;
    struct kernfs_node *kn;
+	struct kernfs_root *root;
    struct inode *inode = NULL;
    const void *ns = NULL;
-	down_read(&kernfs_rwsem);
+	root = kernfs_root(parent);
+	down_read(&root->kernfs_rwsem);
    if (kernfs_ns_enabled(parent))
    	ns = kernfs_info(dir->i_sb)->ns;
@@ -1137,7 +1146,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
    	 * create a negative.
    	 */
    	if (!kernfs_active(kn)) {
-			up_read(&kernfs_rwsem);
+			up_read(&root->kernfs_rwsem);
    		return NULL;
    	}
    	inode = kernfs_get_inode(dir->i_sb, kn);
@@ -1152,7 +1161,7 @@ static struct dentry *kernfs_iop_lookup(struct inode *dir,
     */
    if (!IS_ERR(inode))
    	kernfs_set_rev(parent, dentry);
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
/* instantiate and hash (possibly negative) dentry */
    return d_splice_alias(inode, dentry);
@@ -1275,7 +1284,7 @@ static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
 {
    struct rb_node *rbn;
-	lockdep_assert_held_write(&kernfs_rwsem);
+	lockdep_assert_held_write(&kernfs_root(root)->kernfs_rwsem);
/* if first iteration, visit leftmost descendant which may be root */
    if (!pos)
@@ -1310,8 +1319,9 @@ static struct kernfs_node *kernfs_next_descendant_post(struct kernfs_node *pos,
 void kernfs_activate(struct kernfs_node *kn)
 {
    struct kernfs_node *pos;
+	struct kernfs_root *root = kernfs_root(kn);
-	down_write(&kernfs_rwsem);
+	down_write(&root->kernfs_rwsem);
pos = NULL;
    while ((pos = kernfs_next_descendant_post(pos, kn))) {
@@ -1325,14 +1335,14 @@ void kernfs_activate(struct kernfs_node *kn)
    	pos->flags |= KERNFS_ACTIVATED;
    }
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
 }
static void __kernfs_remove(struct kernfs_node *kn)
 {
    struct kernfs_node *pos;
-	lockdep_assert_held_write(&kernfs_rwsem);
+	lockdep_assert_held_write(&kernfs_root(kn)->kernfs_rwsem);
/*
     * Short-circuit if non-root @kn has already finished removal.
@@ -1402,9 +1412,11 @@ static void __kernfs_remove(struct kernfs_node *kn)
  */
 void kernfs_remove(struct kernfs_node *kn)
 {
-	down_write(&kernfs_rwsem);
+	struct kernfs_root *root = kernfs_root(kn);
+
+	down_write(&root->kernfs_rwsem);
    __kernfs_remove(kn);
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
 }
/**
@@ -1490,8 +1502,9 @@ void kernfs_unbreak_active_protection(struct kernfs_node *kn)
 bool kernfs_remove_self(struct kernfs_node *kn)
 {
    bool ret;
+	struct kernfs_root *root = kernfs_root(kn);
-	down_write(&kernfs_rwsem);
+	down_write(&root->kernfs_rwsem);
    kernfs_break_active_protection(kn);
/*
@@ -1519,9 +1532,9 @@ bool kernfs_remove_self(struct kernfs_node *kn)
    		    atomic_read(&kn->active) == KN_DEACTIVATED_BIAS)
    			break;
-			up_write(&kernfs_rwsem);
+			up_write(&root->kernfs_rwsem);
    		schedule();
-			down_write(&kernfs_rwsem);
+			down_write(&root->kernfs_rwsem);
    	}
    	finish_wait(waitq, &wait);
    	WARN_ON_ONCE(!RB_EMPTY_NODE(&kn->rb));
@@ -1534,7 +1547,7 @@ bool kernfs_remove_self(struct kernfs_node *kn)
     */
    kernfs_unbreak_active_protection(kn);
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
    return ret;
 }
@@ -1551,6 +1564,7 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
    		     const void *ns)
 {
    struct kernfs_node *kn;
+	struct kernfs_root *root;
if (!parent) {
    	WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory\n",
@@ -1558,7 +1572,8 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
    	return -ENOENT;
    }
-	down_write(&kernfs_rwsem);
+	root = kernfs_root(parent);
+	down_write(&root->kernfs_rwsem);
kn = kernfs_find_ns(parent, name, ns);
    if (kn) {
@@ -1567,7 +1582,7 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
    	kernfs_put(kn);
    }
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
if (kn)
    	return 0;
@@ -1586,6 +1601,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
    	     const char *new_name, const void *new_ns)
 {
    struct kernfs_node *old_parent;
+	struct kernfs_root *root;
    const char *old_name = NULL;
    int error;
@@ -1593,7 +1609,8 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
    if (!kn->parent)
    	return -EINVAL;
-	down_write(&kernfs_rwsem);
+	root = kernfs_root(kn);
+	down_write(&root->kernfs_rwsem);
error = -ENOENT;
    if (!kernfs_active(kn) || !kernfs_active(new_parent) ||
@@ -1647,7 +1664,7 @@ int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
error = 0;
  out:
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
    return error;
 }
@@ -1718,11 +1735,14 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
    struct dentry *dentry = file->f_path.dentry;
    struct kernfs_node *parent = kernfs_dentry_node(dentry);
    struct kernfs_node *pos = file->private_data;
+	struct kernfs_root *root;
    const void *ns = NULL;
if (!dir_emit_dots(file, ctx))
    	return 0;
-	down_read(&kernfs_rwsem);
+
+	root = kernfs_root(parent);
+	down_read(&root->kernfs_rwsem);
if (kernfs_ns_enabled(parent))
    	ns = kernfs_info(dentry->d_sb)->ns;
@@ -1739,12 +1759,12 @@ static int kernfs_fop_readdir(struct file *file, struct dir_context *ctx)
    	file->private_data = pos;
    	kernfs_get(pos);
-		up_read(&kernfs_rwsem);
+		up_read(&root->kernfs_rwsem);
    	if (!dir_emit(ctx, name, len, ino, type))
    		return 0;
-		down_read(&kernfs_rwsem);
+		down_read(&root->kernfs_rwsem);
    }
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
    file->private_data = NULL;
    ctx->pos = INT_MAX;
    return 0;
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 60e2a86c535e..9414a7a60a9f 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -847,6 +847,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
 {
    struct kernfs_node *kn;
    struct kernfs_super_info *info;
+	struct kernfs_root *root;
 repeat:
    /* pop one off the notify_list */
    spin_lock_irq(&kernfs_notify_lock);
@@ -859,8 +860,9 @@ static void kernfs_notify_workfn(struct work_struct *work)
    kn->attr.notify_next = NULL;
    spin_unlock_irq(&kernfs_notify_lock);
+	root = kernfs_root(kn);
    /* kick fsnotify */
-	down_write(&kernfs_rwsem);
+	down_write(&root->kernfs_rwsem);
list_for_each_entry(info, &kernfs_root(kn)->supers, node) {
    	struct kernfs_node *parent;
@@ -898,7 +900,7 @@ static void kernfs_notify_workfn(struct work_struct *work)
    	iput(inode);
    }
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
    kernfs_put(kn);
    goto repeat;
 }
diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
index c0eae1725435..3d783d80f5da 100644
--- a/fs/kernfs/inode.c
+++ b/fs/kernfs/inode.c
@@ -99,10 +99,11 @@ int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
 int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
 {
    int ret;
+	struct kernfs_root *root = kernfs_root(kn);
-	down_write(&kernfs_rwsem);
+	down_write(&root->kernfs_rwsem);
    ret = __kernfs_setattr(kn, iattr);
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
    return ret;
 }
@@ -111,12 +112,14 @@ int kernfs_iop_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
 {
    struct inode *inode = d_inode(dentry);
    struct kernfs_node *kn = inode->i_private;
+	struct kernfs_root *root;
    int error;
if (!kn)
    	return -EINVAL;
-	down_write(&kernfs_rwsem);
+	root = kernfs_root(kn);
+	down_write(&root->kernfs_rwsem);
    error = setattr_prepare(&init_user_ns, dentry, iattr);
    if (error)
    	goto out;
@@ -129,7 +132,7 @@ int kernfs_iop_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
    setattr_copy(&init_user_ns, inode, iattr);
out:
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
    return error;
 }
@@ -184,13 +187,14 @@ int kernfs_iop_getattr(struct user_namespace *mnt_userns,
 {
    struct inode *inode = d_inode(path->dentry);
    struct kernfs_node *kn = inode->i_private;
+	struct kernfs_root *root = kernfs_root(kn);
-	down_read(&kernfs_rwsem);
+	down_read(&root->kernfs_rwsem);
    spin_lock(&inode->i_lock);
    kernfs_refresh_inode(kn, inode);
    generic_fillattr(&init_user_ns, inode, stat);
    spin_unlock(&inode->i_lock);
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
return 0;
 }
@@ -274,19 +278,21 @@ int kernfs_iop_permission(struct user_namespace *mnt_userns,
    		  struct inode *inode, int mask)
 {
    struct kernfs_node *kn;
+	struct kernfs_root *root;
    int ret;
if (mask & MAY_NOT_BLOCK)
    	return -ECHILD;
kn = inode->i_private;
+	root = kernfs_root(kn);
-	down_read(&kernfs_rwsem);
+	down_read(&root->kernfs_rwsem);
    spin_lock(&inode->i_lock);
    kernfs_refresh_inode(kn, inode);
    ret = generic_permission(&init_user_ns, inode, mask);
    spin_unlock(&inode->i_lock);
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
return ret;
 }
diff --git a/fs/kernfs/mount.c b/fs/kernfs/mount.c
index f2f909d09f52..cfa79715fc1a 100644
--- a/fs/kernfs/mount.c
+++ b/fs/kernfs/mount.c
@@ -236,6 +236,7 @@ struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
 {
    struct kernfs_super_info *info = kernfs_info(sb);
+	struct kernfs_root *kf_root = kfc->root;
    struct inode *inode;
    struct dentry *root;
@@ -255,9 +256,9 @@ static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *k
    sb->s_shrink.seeks = 0;
/* get root inode, initialize and unlock it */
-	down_read(&kernfs_rwsem);
+	down_read(&kf_root->kernfs_rwsem);
    inode = kernfs_get_inode(sb, info->root->kn);
-	up_read(&kernfs_rwsem);
+	up_read(&kf_root->kernfs_rwsem);
    if (!inode) {
    	pr_debug("kernfs: could not get root inode\n");
    	return -ENOMEM;
@@ -334,6 +335,7 @@ int kernfs_get_tree(struct fs_context *fc)
if (!sb->s_root) {
    	struct kernfs_super_info *info = kernfs_info(sb);
+		struct kernfs_root *root = kfc->root;
kfc->new_sb_created = true;
@@ -344,9 +346,9 @@ int kernfs_get_tree(struct fs_context *fc)
    	}
    	sb->s_flags |= SB_ACTIVE;
-		down_write(&kernfs_rwsem);
+		down_write(&root->kernfs_rwsem);
    	list_add(&info->node, &info->root->supers);
-		up_write(&kernfs_rwsem);
+		up_write(&root->kernfs_rwsem);
    }
fc->root = dget(sb->s_root);
@@ -371,10 +373,11 @@ void kernfs_free_fs_context(struct fs_context *fc)
 void kernfs_kill_sb(struct super_block *sb)
 {
    struct kernfs_super_info *info = kernfs_info(sb);
+	struct kernfs_root *root = info->root;
-	down_write(&kernfs_rwsem);
+	down_write(&root->kernfs_rwsem);
    list_del(&info->node);
-	up_write(&kernfs_rwsem);
+	up_write(&root->kernfs_rwsem);
/*
     * Remove the superblock from fs_supers/s_instances
diff --git a/fs/kernfs/symlink.c b/fs/kernfs/symlink.c
index c8f8e41b8411..efb0b9ca9057 100644
--- a/fs/kernfs/symlink.c
+++ b/fs/kernfs/symlink.c
@@ -114,11 +114,12 @@ static int kernfs_getlink(struct inode *inode, char *path)
    struct kernfs_node *kn = inode->i_private;
    struct kernfs_node *parent = kn->parent;
    struct kernfs_node *target = kn->symlink.target_kn;
+	struct kernfs_root *root = kernfs_root(parent);
    int error;
-	down_read(&kernfs_rwsem);
+	down_read(&root->kernfs_rwsem);
    error = kernfs_get_target_path(parent, target, path);
-	up_read(&kernfs_rwsem);
+	up_read(&root->kernfs_rwsem);
return error;
 }
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 1093abf7c28c..e7078cde3522 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -16,6 +16,7 @@
 #include <linux/atomic.h>
 #include <linux/uidgid.h>
 #include <linux/wait.h>
+#include <linux/rwsem.h>
struct file;
 struct dentry;
@@ -197,6 +198,7 @@ struct kernfs_root {
    struct list_head	supers;
wait_queue_head_t	deactivate_waitq;
+	struct rw_semaphore	kernfs_rwsem;
 };
struct kernfs_open_file {
-- 
2.39.5



    

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[PATCH 5.15] kernfs: switch global kernfs_rwsem lock to per-fs lock