linux-kernel - Re: [PATCH v2] f2fs: fix deadlock in i_xattr_sem and inode page lock and fix the original issue

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Date:   Wed, 28 Jun 2023 11:33:35 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, stable@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: fix deadlock in i_xattr_sem and inode page lock
 and fix the original issue

On 06/28, Chao Yu wrote:
> On 2023/6/28 16:08, Jaegeuk Kim wrote:
> > Thread #1:
> > 
> > [122554.641906][   T92]  f2fs_getxattr+0xd4/0x5fc
> >      -> waiting for f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
> > 
> > [122554.641927][   T92]  __f2fs_get_acl+0x50/0x284
> > [122554.641948][   T92]  f2fs_init_acl+0x84/0x54c
> > [122554.641969][   T92]  f2fs_init_inode_metadata+0x460/0x5f0
> > [122554.641990][   T92]  f2fs_add_inline_entry+0x11c/0x350
> >      -> Locked dir->inode_page by f2fs_get_node_page()
> > 
> > [122554.642009][   T92]  f2fs_do_add_link+0x100/0x1e4
> > [122554.642025][   T92]  f2fs_create+0xf4/0x22c
> > [122554.642047][   T92]  vfs_create+0x130/0x1f4
> > 
> > Thread #2:
> > 
> > [123996.386358][   T92]  __get_node_page+0x8c/0x504
> >      -> waiting for dir->inode_page lock
> > 
> > [123996.386383][   T92]  read_all_xattrs+0x11c/0x1f4
> > [123996.386405][   T92]  __f2fs_setxattr+0xcc/0x528
> > [123996.386424][   T92]  f2fs_setxattr+0x158/0x1f4
> >      -> f2fs_down_write(&F2FS_I(inode)->i_xattr_sem);
> > 
> > [123996.386443][   T92]  __f2fs_set_acl+0x328/0x430
> > [123996.386618][   T92]  f2fs_set_acl+0x38/0x50
> > [123996.386642][   T92]  posix_acl_chmod+0xc8/0x1c8
> > [123996.386669][   T92]  f2fs_setattr+0x5e0/0x6bc
> > [123996.386689][   T92]  notify_change+0x4d8/0x580
> > [123996.386717][   T92]  chmod_common+0xd8/0x184
> > [123996.386748][   T92]  do_fchmodat+0x60/0x124
> > [123996.386766][   T92]  __arm64_sys_fchmodat+0x28/0x3c
> 
> Back to the race condition, my question is why we can chmod on inode before
> it has been created?

This is touching the directory.

> 
> Thanks,
> 
> > 
> > Fixes: 27161f13e3c3 "f2fs: avoid race in between read xattr & write xattr"
> > Cc: <stable@...r.kernel.org>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> > ---
> >   fs/f2fs/dir.c   | 9 ++++++++-
> >   fs/f2fs/xattr.c | 6 ++++--
> >   2 files changed, 12 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> > index 887e55988450..d635c58cf5a3 100644
> > --- a/fs/f2fs/dir.c
> > +++ b/fs/f2fs/dir.c
> > @@ -775,8 +775,15 @@ int f2fs_add_dentry(struct inode *dir, const struct f2fs_filename *fname,
> >   {
> >   	int err = -EAGAIN;
> > -	if (f2fs_has_inline_dentry(dir))
> > +	if (f2fs_has_inline_dentry(dir)) {
> > +		/*
> > +		 * Should get i_xattr_sem to keep the lock order:
> > +		 * i_xattr_sem -> inode_page lock used by f2fs_setxattr.
> > +		 */
> > +		f2fs_down_read(&F2FS_I(dir)->i_xattr_sem);
> >   		err = f2fs_add_inline_entry(dir, fname, inode, ino, mode);
> > +		f2fs_up_read(&F2FS_I(dir)->i_xattr_sem);
> > +	}
> >   	if (err == -EAGAIN)
> >   		err = f2fs_add_regular_entry(dir, fname, inode, ino, mode);
> > diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
> > index 213805d3592c..476b186b90a6 100644
> > --- a/fs/f2fs/xattr.c
> > +++ b/fs/f2fs/xattr.c
> > @@ -528,10 +528,12 @@ int f2fs_getxattr(struct inode *inode, int index, const char *name,
> >   	if (len > F2FS_NAME_LEN)
> >   		return -ERANGE;
> > -	f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
> > +	if (!ipage)
> > +		f2fs_down_read(&F2FS_I(inode)->i_xattr_sem);
> >   	error = lookup_all_xattrs(inode, ipage, index, len, name,
> >   				&entry, &base_addr, &base_size, &is_inline);
> > -	f2fs_up_read(&F2FS_I(inode)->i_xattr_sem);
> > +	if (!ipage)
> > +		f2fs_up_read(&F2FS_I(inode)->i_xattr_sem);
> >   	if (error)
> >   		return error;