Patch "erofs: fix lockdep false positives on initializing erofs_pseudo_mnt" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    erofs: fix lockdep false positives on initializing erofs_pseudo_mnt

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     erofs-fix-lockdep-false-positives-on-initializing-er.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit d381871509b130ac9f1228b5c8c03c42341f8d4f
Author: Baokun Li <libaokun1@xxxxxxxxxx>
Date:   Thu Mar 7 18:10:18 2024 +0800

    erofs: fix lockdep false positives on initializing erofs_pseudo_mnt
    
    [ Upstream commit 0f28be64d132aaf95d06375c8002ad9ecea69d71 ]
    
    Lockdep reported the following issue when mounting erofs with a domain_id:
    
    ============================================
    WARNING: possible recursive locking detected
    6.8.0-rc7-xfstests #521 Not tainted
    --------------------------------------------
    mount/396 is trying to acquire lock:
    ffff907a8aaaa0e0 (&type->s_umount_key#50/1){+.+.}-{3:3},
                                                    at: alloc_super+0xe3/0x3d0
    
    but task is already holding lock:
    ffff907a8aaa90e0 (&type->s_umount_key#50/1){+.+.}-{3:3},
                                                    at: alloc_super+0xe3/0x3d0
    
    other info that might help us debug this:
     Possible unsafe locking scenario:
    
           CPU0
           ----
      lock(&type->s_umount_key#50/1);
      lock(&type->s_umount_key#50/1);
    
     *** DEADLOCK ***
    
     May be due to missing lock nesting notation
    
    2 locks held by mount/396:
     #0: ffff907a8aaa90e0 (&type->s_umount_key#50/1){+.+.}-{3:3},
                            at: alloc_super+0xe3/0x3d0
     #1: ffffffffc00e6f28 (erofs_domain_list_lock){+.+.}-{3:3},
                            at: erofs_fscache_register_fs+0x3d/0x270 [erofs]
    
    stack backtrace:
    CPU: 1 PID: 396 Comm: mount Not tainted 6.8.0-rc7-xfstests #521
    Call Trace:
     <TASK>
     dump_stack_lvl+0x64/0xb0
     validate_chain+0x5c4/0xa00
     __lock_acquire+0x6a9/0xd50
     lock_acquire+0xcd/0x2b0
     down_write_nested+0x45/0xd0
     alloc_super+0xe3/0x3d0
     sget_fc+0x62/0x2f0
     vfs_get_super+0x21/0x90
     vfs_get_tree+0x2c/0xf0
     fc_mount+0x12/0x40
     vfs_kern_mount.part.0+0x75/0x90
     kern_mount+0x24/0x40
     erofs_fscache_register_fs+0x1ef/0x270 [erofs]
     erofs_fc_fill_super+0x213/0x380 [erofs]
    
    This is because the file_system_type of both erofs and the pseudo-mount
    point of domain_id is erofs_fs_type, so two successive calls to
    alloc_super() are considered to be using the same lock and trigger the
    warning above.
    
    Therefore add a nodev file_system_type called erofs_anon_fs_type in
    fscache.c to silence this complaint. Because kern_mount() takes a
    pointer to struct file_system_type, not its (string) name. So we don't
    need to call register_filesystem(). In addition, call init_pseudo() in
    erofs_anon_init_fs_context() as suggested by Al Viro, so that we can
    remove erofs_fc_fill_pseudo_super(), erofs_fc_anon_get_tree(), and
    erofs_anon_context_ops.
    
    Suggested-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
    Fixes: a9849560c55e ("erofs: introduce a pseudo mnt to manage shared cookies")
    Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
    Reviewed-and-tested-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
    Reviewed-by: Yang Erkun <yangerkun@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240307101018.2021925-1-libaokun1@xxxxxxxxxx
    Signed-off-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 1052f75d1dfae..afc37c9029ce7 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -3,6 +3,7 @@
  * Copyright (C) 2022, Alibaba Cloud
  * Copyright (C) 2022, Bytedance Inc. All rights reserved.
  */
+#include <linux/pseudo_fs.h>
 #include <linux/fscache.h>
 #include "internal.h"
 
@@ -12,6 +13,18 @@ static LIST_HEAD(erofs_domain_list);
 static LIST_HEAD(erofs_domain_cookies_list);
 static struct vfsmount *erofs_pseudo_mnt;
 
+static int erofs_anon_init_fs_context(struct fs_context *fc)
+{
+	return init_pseudo(fc, EROFS_SUPER_MAGIC) ? 0 : -ENOMEM;
+}
+
+static struct file_system_type erofs_anon_fs_type = {
+	.owner		= THIS_MODULE,
+	.name           = "pseudo_erofs",
+	.init_fs_context = erofs_anon_init_fs_context,
+	.kill_sb        = kill_anon_super,
+};
+
 struct erofs_fscache_request {
 	struct erofs_fscache_request *primary;
 	struct netfs_cache_resources cache_resources;
@@ -381,7 +394,7 @@ static int erofs_fscache_init_domain(struct super_block *sb)
 		goto out;
 
 	if (!erofs_pseudo_mnt) {
-		struct vfsmount *mnt = kern_mount(&erofs_fs_type);
+		struct vfsmount *mnt = kern_mount(&erofs_anon_fs_type);
 		if (IS_ERR(mnt)) {
 			err = PTR_ERR(mnt);
 			goto out;
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index eb062f19b766a..1a4fe9f60295c 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -385,7 +385,6 @@ struct erofs_map_dev {
 	unsigned int m_deviceid;
 };
 
-extern struct file_system_type erofs_fs_type;
 extern const struct super_operations erofs_sops;
 
 extern const struct address_space_operations erofs_raw_access_aops;
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 4e1ca36987685..c9f9a43197db6 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -575,13 +575,6 @@ static const struct export_operations erofs_export_ops = {
 	.get_parent = erofs_get_parent,
 };
 
-static int erofs_fc_fill_pseudo_super(struct super_block *sb, struct fs_context *fc)
-{
-	static const struct tree_descr empty_descr = {""};
-
-	return simple_fill_super(sb, EROFS_SUPER_MAGIC, &empty_descr);
-}
-
 static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	struct inode *inode;
@@ -708,11 +701,6 @@ static int erofs_fc_fill_super(struct super_block *sb, struct fs_context *fc)
 	return 0;
 }
 
-static int erofs_fc_anon_get_tree(struct fs_context *fc)
-{
-	return get_tree_nodev(fc, erofs_fc_fill_pseudo_super);
-}
-
 static int erofs_fc_get_tree(struct fs_context *fc)
 {
 	struct erofs_fs_context *ctx = fc->fs_private;
@@ -785,20 +773,10 @@ static const struct fs_context_operations erofs_context_ops = {
 	.free		= erofs_fc_free,
 };
 
-static const struct fs_context_operations erofs_anon_context_ops = {
-	.get_tree       = erofs_fc_anon_get_tree,
-};
-
 static int erofs_init_fs_context(struct fs_context *fc)
 {
 	struct erofs_fs_context *ctx;
 
-	/* pseudo mount for anon inodes */
-	if (fc->sb_flags & SB_KERNMOUNT) {
-		fc->ops = &erofs_anon_context_ops;
-		return 0;
-	}
-
 	ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
@@ -820,12 +798,6 @@ static void erofs_kill_sb(struct super_block *sb)
 {
 	struct erofs_sb_info *sbi;
 
-	/* pseudo mount for anon inodes */
-	if (sb->s_flags & SB_KERNMOUNT) {
-		kill_anon_super(sb);
-		return;
-	}
-
 	if (erofs_is_fscache_mode(sb))
 		kill_anon_super(sb);
 	else
@@ -864,7 +836,7 @@ static void erofs_put_super(struct super_block *sb)
 	erofs_fscache_unregister_fs(sb);
 }
 
-struct file_system_type erofs_fs_type = {
+static struct file_system_type erofs_fs_type = {
 	.owner          = THIS_MODULE,
 	.name           = "erofs",
 	.init_fs_context = erofs_init_fs_context,




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