[PATCH] erofs: fix lockdep false positives on initializing erofs_pseudo_mnt
From: Baokun Li
Date: Wed Mar 06 2024 - 21:44:02 EST
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 named erofs_anon_fs_type to
silence this complaint. In addition, to reduce code coupling, refactor
out the erofs_anon_init_fs_context() and erofs_kill_pseudo_sb() functions
and move the erofs_pseudo_mnt related code to fscache.c.
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
fs/erofs/fscache.c | 48 ++++++++++++++++++++++++++++++++++++++++++++-
fs/erofs/internal.h | 10 +++++++++-
fs/erofs/super.c | 37 ++++++++--------------------------
3 files changed, 64 insertions(+), 31 deletions(-)
diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
index 89a7c2453aae..a346884a2c00 100644
--- a/fs/erofs/fscache.c
+++ b/fs/erofs/fscache.c
@@ -4,6 +4,7 @@
* Copyright (C) 2022, Bytedance Inc. All rights reserved.
*/
#include <linux/fscache.h>
+#include <linux/fs_context.h>
#include "internal.h"
static DEFINE_MUTEX(erofs_domain_list_lock);
@@ -12,6 +13,51 @@ static LIST_HEAD(erofs_domain_list);
static LIST_HEAD(erofs_domain_cookies_list);
static struct vfsmount *erofs_pseudo_mnt;
+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_anon_get_tree(struct fs_context *fc)
+{
+ return get_tree_nodev(fc, erofs_fc_fill_pseudo_super);
+}
+
+static const struct fs_context_operations erofs_anon_context_ops = {
+ .get_tree = erofs_fc_anon_get_tree,
+};
+
+static int erofs_anon_init_fs_context(struct fs_context *fc)
+{
+ fc->ops = &erofs_anon_context_ops;
+ return 0;
+}
+
+static void erofs_kill_pseudo_sb(struct super_block *sb)
+{
+ kill_anon_super(sb);
+}
+
+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 = erofs_kill_pseudo_sb,
+};
+
+int erofs_anon_register_fs(void)
+{
+ return register_filesystem(&erofs_anon_fs_type);
+}
+
+void erofs_anon_unregister_fs(void)
+{
+ unregister_filesystem(&erofs_anon_fs_type);
+}
+
struct erofs_fscache_request {
struct erofs_fscache_request *primary;
struct netfs_cache_resources cache_resources;
@@ -381,7 +427,7 @@ 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..d9e30ccceb39 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;
@@ -507,6 +506,9 @@ static inline int z_erofs_deflate_exit(void) { return 0; }
#endif /* !CONFIG_EROFS_FS_ZIP_DEFLATE */
#ifdef CONFIG_EROFS_FS_ONDEMAND
+int erofs_anon_register_fs(void);
+void erofs_anon_unregister_fs(void);
+
int erofs_fscache_register_fs(struct super_block *sb);
void erofs_fscache_unregister_fs(struct super_block *sb);
@@ -514,6 +516,12 @@ struct erofs_fscache *erofs_fscache_register_cookie(struct super_block *sb,
char *name, unsigned int flags);
void erofs_fscache_unregister_cookie(struct erofs_fscache *fscache);
#else
+static inline int erofs_anon_register_fs(void)
+{
+ return 0;
+}
+static inline void erofs_anon_unregister_fs(void) {}
+
static inline int erofs_fscache_register_fs(struct super_block *sb)
{
return -EOPNOTSUPP;
diff --git a/fs/erofs/super.c b/fs/erofs/super.c
index 9b4b66dcdd4f..a745010e9fe6 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,
@@ -911,6 +883,10 @@ static int __init erofs_module_init(void)
if (err)
goto sysfs_err;
+ err = erofs_anon_register_fs();
+ if (err)
+ goto anon_err;
+
err = register_filesystem(&erofs_fs_type);
if (err)
goto fs_err;
@@ -918,6 +894,8 @@ static int __init erofs_module_init(void)
return 0;
fs_err:
+ erofs_anon_unregister_fs();
+anon_err:
erofs_exit_sysfs();
sysfs_err:
z_erofs_exit_zip_subsystem();
@@ -935,6 +913,7 @@ static int __init erofs_module_init(void)
static void __exit erofs_module_exit(void)
{
unregister_filesystem(&erofs_fs_type);
+ erofs_anon_unregister_fs();
/* Ensure all RCU free inodes / pclusters are safe to be destroyed. */
rcu_barrier();
--
2.31.1