[dm-devel] [PATCH 1/5] blk-mq: introduce BLK_STS_DEV_RESOURCE

[Bart Van Assche]

On Wed, 2018-01-24 at 00:41 +0800, Ming Lei wrote:
> Could you explain where to call call_rcu()?  call_rcu() can't be used in
> IO path at all.

Can you explain what makes you think that call_rcu() can't be used in the
I/O path? As you know call_rcu() invokes a function asynchronously. From
Documentation/RCU/Design/Requirements/Requirements.html:

  The <tt>call_rcu()</tt> function may be used in a number of
  situations where neither <tt>synchronize_rcu()</tt> nor
  <tt>synchronize_rcu_expedited()</tt> would be legal,
  including within preempt-disable code, <tt>local_bh_disable()</tt> code,
  interrupt-disable code, and interrupt handlers.

Bart.