On Thu, Nov 28, 2019 at 12:03:04PM -0500, Meng Xu wrote:
> 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?
This makes no sense. The inodes corresponding to "sym_foo" and "bar"
are completely differenth. So why would there be a data race?
How are you concluding that that there is, in fact, a data race?
- Ted
