FROMLIST: f2fs: remove i_xattr_sem to avoid deadlock and fix the original issue

This reverts commit 27161f13 "f2fs: avoid race in between read xattr & write xattr".

That introduced a deadlock case:

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

Let's take a look at the original issue back.

Thread A:                                       Thread B:
-f2fs_getxattr
   -lookup_all_xattrs
      -xnid = F2FS_I(inode)->i_xattr_nid;
                                                -f2fs_setxattr
                                                    -__f2fs_setxattr
                                                        -write_all_xattrs
                                                            -truncate_xattr_node
                                                                  ...  ...
                                                -write_checkpoint
                                                                  ...  ...
                                                -alloc_nid   <- nid reuse
          -get_node_page
              -f2fs_bug_on  <- nid != node_footer->nid

I think we don't need to truncate xattr pages eagerly which introduces lots of
data races without big benefits.

Bug: 280545073
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/linux-f2fs-devel/20230613233940.3643362-1-jaegeuk@kernel.org/T/#u


Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Change-Id: Ifdbaf7defa50b479d82d2c945aa9d48e2e2317ed