Re: [f2fs-dev] [PATCH] f2fs: avoid false alarm of circular locking

[Guenter Roeck]

On Fri, Aug 18, 2023 at 05:30:12PM -0700, Jaegeuk Kim wrote:
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.5.0-rc5-syzkaller-00353-gae545c3283dc #0 Not tainted
> ------------------------------------------------------
> syz-executor273/5027 is trying to acquire lock:
> ffff888077fe1fb0 (&fi->i_sem){+.+.}-{3:3}, at: f2fs_down_write fs/f2fs/f2fs.h:2133 [inline]
> ffff888077fe1fb0 (&fi->i_sem){+.+.}-{3:3}, at: f2fs_add_inline_entry+0x300/0x6f0 fs/f2fs/inline.c:644
> 
> but task is already holding lock:
> ffff888077fe07c8 (&fi->i_xattr_sem){.+.+}-{3:3}, at: f2fs_down_read fs/f2fs/f2fs.h:2108 [inline]
> ffff888077fe07c8 (&fi->i_xattr_sem){.+.+}-{3:3}, at: f2fs_add_dentry+0x92/0x230 fs/f2fs/dir.c:783
> 
> which lock already depends on the new lock.
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #1 (&fi->i_xattr_sem){.+.+}-{3:3}:
>        down_read+0x9c/0x470 kernel/locking/rwsem.c:1520
>        f2fs_down_read fs/f2fs/f2fs.h:2108 [inline]
>        f2fs_getxattr+0xb1e/0x12c0 fs/f2fs/xattr.c:532
>        __f2fs_get_acl+0x5a/0x900 fs/f2fs/acl.c:179
>        f2fs_acl_create fs/f2fs/acl.c:377 [inline]
>        f2fs_init_acl+0x15c/0xb30 fs/f2fs/acl.c:420
>        f2fs_init_inode_metadata+0x159/0x1290 fs/f2fs/dir.c:558
>        f2fs_add_regular_entry+0x79e/0xb90 fs/f2fs/dir.c:740
>        f2fs_add_dentry+0x1de/0x230 fs/f2fs/dir.c:788
>        f2fs_do_add_link+0x190/0x280 fs/f2fs/dir.c:827
>        f2fs_add_link fs/f2fs/f2fs.h:3554 [inline]
>        f2fs_mkdir+0x377/0x620 fs/f2fs/namei.c:781
>        vfs_mkdir+0x532/0x7e0 fs/namei.c:4117
>        do_mkdirat+0x2a9/0x330 fs/namei.c:4140
>        __do_sys_mkdir fs/namei.c:4160 [inline]
>        __se_sys_mkdir fs/namei.c:4158 [inline]
>        __x64_sys_mkdir+0xf2/0x140 fs/namei.c:4158
>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>        do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> -> #0 (&fi->i_sem){+.+.}-{3:3}:
>        check_prev_add kernel/locking/lockdep.c:3142 [inline]
>        check_prevs_add kernel/locking/lockdep.c:3261 [inline]
>        validate_chain kernel/locking/lockdep.c:3876 [inline]
>        __lock_acquire+0x2e3d/0x5de0 kernel/locking/lockdep.c:5144
>        lock_acquire kernel/locking/lockdep.c:5761 [inline]
>        lock_acquire+0x1ae/0x510 kernel/locking/lockdep.c:5726
>        down_write+0x93/0x200 kernel/locking/rwsem.c:1573
>        f2fs_down_write fs/f2fs/f2fs.h:2133 [inline]
>        f2fs_add_inline_entry+0x300/0x6f0 fs/f2fs/inline.c:644
>        f2fs_add_dentry+0xa6/0x230 fs/f2fs/dir.c:784
>        f2fs_do_add_link+0x190/0x280 fs/f2fs/dir.c:827
>        f2fs_add_link fs/f2fs/f2fs.h:3554 [inline]
>        f2fs_mkdir+0x377/0x620 fs/f2fs/namei.c:781
>        vfs_mkdir+0x532/0x7e0 fs/namei.c:4117
>        ovl_do_mkdir fs/overlayfs/overlayfs.h:196 [inline]
>        ovl_mkdir_real+0xb5/0x370 fs/overlayfs/dir.c:146
>        ovl_workdir_create+0x3de/0x820 fs/overlayfs/super.c:309
>        ovl_make_workdir fs/overlayfs/super.c:711 [inline]
>        ovl_get_workdir fs/overlayfs/super.c:864 [inline]
>        ovl_fill_super+0xdab/0x6180 fs/overlayfs/super.c:1400
>        vfs_get_super+0xf9/0x290 fs/super.c:1152
>        vfs_get_tree+0x88/0x350 fs/super.c:1519
>        do_new_mount fs/namespace.c:3335 [inline]
>        path_mount+0x1492/0x1ed0 fs/namespace.c:3662
>        do_mount fs/namespace.c:3675 [inline]
>        __do_sys_mount fs/namespace.c:3884 [inline]
>        __se_sys_mount fs/namespace.c:3861 [inline]
>        __x64_sys_mount+0x293/0x310 fs/namespace.c:3861
>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>        do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> other info that might help us debug this:
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   rlock(&fi->i_xattr_sem);
>                                lock(&fi->i_sem);
>                                lock(&fi->i_xattr_sem);
>   lock(&fi->i_sem);
> 
> Reported-and-tested-by: syzbot+e5600587fa9cbf8e3826@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 5eda1ad1aaff "f2fs: fix deadlock in i_xattr_sem and inode page lock"
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>

Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

> ---
>  fs/f2fs/f2fs.h   | 24 +++++++++++++++---------
>  fs/f2fs/inline.c |  3 ++-
>  2 files changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index c602ff2403b6..c0b7417f1d87 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -2122,15 +2122,6 @@ static inline int f2fs_down_read_trylock(struct f2fs_rwsem *sem)
>  	return down_read_trylock(&sem->internal_rwsem);
>  }
>  
> -#ifdef CONFIG_DEBUG_LOCK_ALLOC
> -static inline void f2fs_down_read_nested(struct f2fs_rwsem *sem, int subclass)
> -{
> -	down_read_nested(&sem->internal_rwsem, subclass);
> -}
> -#else
> -#define f2fs_down_read_nested(sem, subclass) f2fs_down_read(sem)
> -#endif
> -
>  static inline void f2fs_up_read(struct f2fs_rwsem *sem)
>  {
>  	up_read(&sem->internal_rwsem);
> @@ -2141,6 +2132,21 @@ static inline void f2fs_down_write(struct f2fs_rwsem *sem)
>  	down_write(&sem->internal_rwsem);
>  }
>  
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +static inline void f2fs_down_read_nested(struct f2fs_rwsem *sem, int subclass)
> +{
> +	down_read_nested(&sem->internal_rwsem, subclass);
> +}
> +
> +static inline void f2fs_down_write_nested(struct f2fs_rwsem *sem, int subclass)
> +{
> +	down_write_nested(&sem->internal_rwsem, subclass);
> +}
> +#else
> +#define f2fs_down_read_nested(sem, subclass) f2fs_down_read(sem)
> +#define f2fs_down_write_nested(sem, subclass) f2fs_down_write(sem)
> +#endif
> +
>  static inline int f2fs_down_write_trylock(struct f2fs_rwsem *sem)
>  {
>  	return down_write_trylock(&sem->internal_rwsem);
> diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
> index 4638fee16a91..0d185ad5e469 100644
> --- a/fs/f2fs/inline.c
> +++ b/fs/f2fs/inline.c
> @@ -641,7 +641,8 @@ int f2fs_add_inline_entry(struct inode *dir, const struct f2fs_filename *fname,
>  	}
>  
>  	if (inode) {
> -		f2fs_down_write(&F2FS_I(inode)->i_sem);
> +		f2fs_down_write_nested(&F2FS_I(inode)->i_sem,
> +						SINGLE_DEPTH_NESTING);
>  		page = f2fs_init_inode_metadata(inode, dir, fname, ipage);
>  		if (IS_ERR(page)) {
>  			err = PTR_ERR(page);
> -- 
> 2.42.0.rc1.204.g551eb34607-goog
> 
> 
> 
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