On Tue, Aug 05, 2014 at 11:38:44AM +0400, Ilya Dryomov wrote:
> While it was never a good idea to sleep in request_fn(), commit
> 34c6bc2c919a ("locking/mutexes: Add extra reschedule point") made it
> a *bad* idea. mutex_lock() since 3.15 may reschedule *before* putting
> task on the mutex wait queue, which for tasks in !TASK_RUNNING state
> means block forever. request_fn() may be called with !TASK_RUNNING on
> the way to schedule() in io_schedule().
>
> Offload request handling to a workqueue, one per rbd device, to avoid
> calling blocking primitives from rbd_request_fn().
Btw, for the future you might want to consider converting rbd to use the
blk-mq infrastructure, which calls the I/O submission function from user
context and will allow you to sleep.
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