[PATCH v2] erofs: fix lockdep false positives on initializing erofs_pseudo_mnt

[PATCH v2] erofs: fix lockdep false positives on initializing erofs_pseudo_mnt

[Baokun Li]

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.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
V1->V2:
	Modified as suggested by Al Viro to simplify the code.

 fs/erofs/fscache.c  | 15 ++++++++++++++-
 fs/erofs/internal.h |  1 -
 fs/erofs/super.c    | 30 +-----------------------------
 3 files changed, 15 insertions(+), 31 deletions(-)

diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 89a7c2453aae..122a4753ecea 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 0f0706325b7b..701d4eec693a 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 9b4b66dcdd4f..6fbb1fba2d31 100644
--- a/fs/erofs/super.c
+++ b/fs/erofs/super.c
@@ -579,13 +579,6 @@ 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;
@@ -712,11 +705,6 @@ 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;
@@ -789,20 +777,10 @@ 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;
@@ -824,12 +802,6 @@ 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
@@ -868,7 +840,7 @@ 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,
-- 
2.31.1

Re: [PATCH v2] erofs: fix lockdep false positives on initializing erofs_pseudo_mnt

[yangerkun]

LGTM

Reviewed-by: Yang Erkun <yangerkun@huawei.com>

在 2024/3/7 18:10, Baokun Li 写道:
> 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.
> 
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> ---
> V1->V2:
> 	Modified as suggested by Al Viro to simplify the code.
> 
>   fs/erofs/fscache.c  | 15 ++++++++++++++-
>   fs/erofs/internal.h |  1 -
>   fs/erofs/super.c    | 30 +-----------------------------
>   3 files changed, 15 insertions(+), 31 deletions(-)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index 89a7c2453aae..122a4753ecea 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 0f0706325b7b..701d4eec693a 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 9b4b66dcdd4f..6fbb1fba2d31 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -579,13 +579,6 @@ 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;
> @@ -712,11 +705,6 @@ 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;
> @@ -789,20 +777,10 @@ 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;
> @@ -824,12 +802,6 @@ 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
> @@ -868,7 +840,7 @@ 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,

Re: [PATCH v2] erofs: fix lockdep false positives on initializing erofs_pseudo_mnt

[Jingbo Xu]

On 3/7/24 6:10 PM, Baokun Li wrote:
> 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.
> 
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

LGTM.

Reviewed-and-tested-by: Jingbo Xu <jefflexu@linux.alibaba.com>

> ---
> V1->V2:
> 	Modified as suggested by Al Viro to simplify the code.
> 
>  fs/erofs/fscache.c  | 15 ++++++++++++++-
>  fs/erofs/internal.h |  1 -
>  fs/erofs/super.c    | 30 +-----------------------------
>  3 files changed, 15 insertions(+), 31 deletions(-)
> 
> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
> index 89a7c2453aae..122a4753ecea 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 0f0706325b7b..701d4eec693a 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 9b4b66dcdd4f..6fbb1fba2d31 100644
> --- a/fs/erofs/super.c
> +++ b/fs/erofs/super.c
> @@ -579,13 +579,6 @@ 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;
> @@ -712,11 +705,6 @@ 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;
> @@ -789,20 +777,10 @@ 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;
> @@ -824,12 +802,6 @@ 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
> @@ -868,7 +840,7 @@ 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,

-- 
Thanks,
Jingbo

Re: [PATCH v2] erofs: fix lockdep false positives on initializing erofs_pseudo_mnt

[Gao Xiang]

On 2024/3/7 18:10, Baokun Li wrote:
> 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.
> 
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

I will add

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>

when applying..

Also since it's a false positive and too close to the
final so let's keep this patch in -next for a while and
then aim for v6.9-rc1 instead.

Thanks,
Gao Xiang

Re: [PATCH v2] erofs: fix lockdep false positives on initializing erofs_pseudo_mnt

[Baokun Li]

On 2024/3/7 22:18, Gao Xiang wrote:
>
>
> On 2024/3/7 18:10, Baokun Li wrote:
>> 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.
>>
>> Signed-off-by: Baokun Li <libaokun1@huawei.com>
>
> I will add
>
> Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
>
> when applying..
Okay, thanks for adding it.
>
> Also since it's a false positive and too close to the
> final so let's keep this patch in -next for a while and
> then aim for v6.9-rc1 instead.
>
> Thanks,
> Gao Xiang
Fine! Thanks!
-- 
With Best Regards,
Baokun Li
.