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Date: Thu, 7 Mar 2024 20:43:08 +0800
From: Jingbo Xu <jefflexu@...ux.alibaba.com>
To: Baokun Li <libaokun1@...wei.com>, linux-erofs@...ts.ozlabs.org
Cc: xiang@...nel.org, chao@...nel.org, huyue2@...lpad.com,
viro@...iv.linux.org.uk, brauner@...nel.org, linux-kernel@...r.kernel.org,
yangerkun@...wei.com, houtao1@...wei.com, yukuai3@...wei.com,
chengzhihao1@...wei.com
Subject: Re: [PATCH v2] erofs: fix lockdep false positives on initializing
erofs_pseudo_mnt
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@...wei.com>
LGTM.
Reviewed-and-tested-by: Jingbo Xu <jefflexu@...ux.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
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