Re: INFO: task hung in __sb_start_write

From: Peter Zijlstra
Date: Mon Jun 11 2018 - 03:31:01 EST

On Sun, Jun 10, 2018 at 11:47:56PM +0900, Tetsuo Handa wrote:

> This looks quite strange that nobody is holding percpu_rw_semaphore for
> write but everybody is stuck trying to hold it for read. (Since there
> is no "X locks held by ..." line without followup "#0:" line, there is
> no possibility that somebody is in TASK_RUNNING state while holding
> percpu_rw_semaphore for write.)
> I feel that either API has a bug or API usage is wrong.
> Any idea for debugging this?

Look at percpu_rwsem_release() and usage. The whole fs freezer thing is