[LU-12382] Deadloop on tiny write

• Type: Bug
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.13.0, Lustre 2.12.3
• Severity: 3
• Assignee: Wang Shilong (Inactive)
• Reporter: Wang Shilong (Inactive)

Description

For a small write(<4K), we will use tiny write and __generic_file_write_iter() will be called to handle it. On newer kernel(4.14 etc), the function is exported and will do something like following:

    |->__generic_file_write_iter
      |->generic_write_perform()

 

If iov_iter_count() passed in is 0, generic_write_perform() will try go to forever loop as bytes copied is always calculated as 0.

The problem is VFS doesn't always skip IO count zero before it comes to lower layer read/write hook, and we should do it by ourselves.

Issue Links

• is related to: LU-12721 HPE MPT MPI and lustre2.12 clients causes write hangs