linux-kernel - Re: [PATCH] sched: Avoid that __wait_on_bit

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Message-ID: <8003deba-7190-8a05-aa81-2b76f0643756@sandisk.com>
Date:	Thu, 4 Aug 2016 07:31:48 -0700
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Oleg Nesterov <oleg@...hat.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Neil Brown <neilb@...e.de>,
	Michael Shaver <jmshaver@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: Avoid that __wait_on_bit_lock() hangs

On 08/04/16 07:09, Peter Zijlstra wrote:
> But I'd still like to understand where we loose the wakeup. What are you
> doing to reproduce this issue?

Hello Peter,

The test I run is as follows:
* Configure the ib_srpt driver to export a RAM disk through the SRP
   protocol. The ib_srpt driver is a LIO target driver that implements
   the SRP protocol, a SCSI transport protocol.
* On the same system, let the ib_srp (SRP initiator) driver log in
   to the ib_srpt driver using the loopback capability of a local
   InfiniBand HCA.
* Run fio with data verification enabled on top of multipath (dm-mpath)
   with queue_if_no_path enabled and let multipath use the SRP paths.
* Simulate cable pulls and reinserts by periodically writing in the
   /sys/class/srp_remote_ports/*/delete and by logging in again. Writing
   into the delete attribute triggers scsi_remove_host() and hence also
   removal of the block device associated with the SCSI device.

The scripts I use to run this test are available at 
https://github.com/bvanassche/srp-test. Since the softRoCE driver is not 
yet upstream running this test requires at least one InfiniBand HCA.

Thanks,

Bart.