Ye Bin 83f99de1b7 ext2: fix race between setxattr and write back
There's an issue when allocating xattrs as follows:
Block Allocation Reservation Windows Map (ext2_try_to_allocate_with_rsv):
reservation window 0x000000006f105382 start: 0, end: 0
reservation window 0x000000008fd1a555 start: 1044, end: 1059
Window map complete.
kernel BUG at fs/ext2/balloc.c:1158!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
RIP: 0010:ext2_try_to_allocate_with_rsv.isra.0+0x15c4/0x1800
Call Trace:
 <TASK>
 ext2_new_blocks+0x935/0x1690
 ext2_new_block+0x73/0xa0
 ext2_xattr_set2+0x74f/0x1730
 ext2_xattr_set+0x12b6/0x2260
 ext2_xattr_user_set+0x9c/0x110
 __vfs_setxattr+0x139/0x1d0
 __vfs_setxattr_noperm+0xfc/0x370
 __vfs_setxattr_locked+0x205/0x2c0
 vfs_setxattr+0x19d/0x3b0
 do_setxattr+0xff/0x220
 setxattr+0x123/0x150
 path_setxattr+0x193/0x1e0
 __x64_sys_setxattr+0xc8/0x170
 do_syscall_64+0x35/0x80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Above issue may happens as follows:
        setxattr                             write back
ext2_xattr_set
  ext2_xattr_set2
    ext2_new_block
      ext2_new_blocks
        ext2_try_to_allocate_with_rsv
          alloc_new_reservation
          --> group=0 [0, 1023] rsv [1016, 1023]
                                        do_writepages
                                          mpage_writepages
                                            write_cache_pages
                                              __mpage_writepage
                                                ext2_get_block
                                                  ext2_get_blocks
                                                   ext2_alloc_branch
                                                    ext2_new_blocks
                                                     ext2_try_to_allocate_with_rsv
                                                       alloc_new_reservation
                                     -->group=1 [1024, 2047] rsv [1044, 1059]
          if ((my_rsv->rsv_start > group_last_block) ||
              (my_rsv->rsv_end < group_first_block)
              rsv_window_dump
              BUG();

Now ext2 mkwrite doesn't allocate new blocks so for these cases we may
be allocating blocks during writeback. However, there is no protection
between ext2_xattr_set() and do_writepages() so these two functions can
conflict on handling the reservation window.  To solve about issue don't
use the reservation window when allocating block for xattr.

Signed-off-by: Ye Bin <yebin10@huawei.com>
Message-Id: <20230815112612.221145-4-yebin10@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
2023-08-16 17:47:37 +02:00
2022-09-28 09:02:20 +02:00

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.
Description
No description provided
Readme 7.9 GiB
Languages
C 97.7%
Assembly 1.6%
Makefile 0.3%
Perl 0.1%