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From: Meng Xu <mengxu.gatech@gmail.com>
To: linux-ext4@vger.kernel.org
Subject: potential data race on ext_inode_hdr(inode)->eh_depth, ext_inode_hdr(inode)->eh_max between a creat and unlink syscall
Date: Thu, 28 Nov 2019 12:03:04 -0500	[thread overview]
Message-ID: <CAAwBoOLoHTZGWFw5y_3MoMgZDQ3gCUQrsAO8Z=U4RwV9KyA_fA@mail.gmail.com> (raw)

Hi Ext4 Developers,

I notice a potential data race on ext_inode_hdr(inode)->eh_depth,
ext_inode_hdr(inode)->eh_max between a create and unlink syscall.
Following is the trace:

[Setup]
mkdir("foo", 511) = 0;
open("foo", 65536, 511) = 3;
create("bar", 511) = 4;
symlink("foo", "sym_foo") = 0;
open("sym_foo", 65536, 511) = 5;

[Thread 1]
create("bar", 438);

__do_sys_creat
  ksys_open
    do_filp_open
      path_openat
        do_last
          handle_truncate
            do_truncate
              notify_change
                ext4_setattr
                  ext4_truncate
                    ext4_ext_truncate
                      ext4_ext _remove_space
                        [WRITE, 2 bytes] ext_inode_hdr(inode)->eh_depth = 0;
                        [WRITE, 2 bytes] ext_inode_hdr(inode)->eh_max
= cpu_to_le16(ext4_ext_space_root(inode, 0));

[Thread 2]
unlink("sym_foo");

__do_sys_unlink
  do_unlinkat
    iput
      iput_final
        evict
          ext4_evict_inode
            ext4_orphan_del
              ext4_mark_iloc_dirty
                ext4_do_update_inode
                  [READ, 4 bytes] raw_inode->i_block[block] = ei->i_data[block];


I could observe that the order between the READ and WRITE is not
deterministic and I was curious what will happen if the READ takes
place in the middle of the two WRITES? Does it cause any damages or
violations?

Best Regards,
Meng

             reply	other threads:[~2019-11-28 17:03 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-28 17:03 Meng Xu [this message]
2019-11-28 23:19 ` potential data race on ext_inode_hdr(inode)->eh_depth, ext_inode_hdr(inode)->eh_max between a creat and unlink syscall Theodore Y. Ts'o
2019-11-29  4:43   ` Meng Xu

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