[LU-17753] ll_merge_attr() may report wrong timestamps for racing stat()-s

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Severity: 3
• Assignee: Vladimir Saveliev
• Reporter: Vladimir Saveliev

Description

The following race between stats may lead to wrong timestamps provided to stat:

Process 1
stat("file")
  ll_getattr_dentry
    ll_glimpse_size
      ll_merge_attr_nolock
        inode_set_mtime(inode, lli->lli_mtime, 0)
        ..
        inode_set_mtime(inode, mtime, 0)

Process 2
stat("file")
  ll_getattr_dentry
    ll_glimpse_size
      ll_merge_attr_nolock
        inode_set_mtime(inode, lli->lli_mtime, 0)

Process 1
    stat->mtime = inode_get_mtime(inode);   <<< wrong mtime gets to stat