linux-kernel - Re: [PATCH 3/3] target: simplify target_wait_for_sess

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Date:	Tue, 14 May 2013 20:05:30 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Jörn Engel <joern@...fs.org>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	target-devel <target-devel@...r.kernel.org>
Subject: Re: [PATCH 3/3] target: simplify target_wait_for_sess_cmds()

On Tue, 2013-05-14 at 12:29 -0400, Jörn Engel wrote:
> On Mon, 13 May 2013 20:08:44 -0700, Nicholas A. Bellinger wrote:
> > On Mon, 2013-05-13 at 18:00 -0400, Jörn Engel wrote:
> > > 
> > > I agree that the overhead doesn't matter.  The msleep(100) spells this
> > > out rather explicitly.  What does matter is that a) the patch retains
> > > old behaviour with much simpler code and b) it fixes a race that kills
> > > the machine.  I can live without a, but very much want to keep b. ;)
> > 
> > Fucking around with ->sess_cmd_lock during each loop of ->sess_cmd_list
> > in target_wait_for_sess_cmds is not simpler code..
> 
> I could argue that fucking around with ->sess_cmd_lock during each
> loop is simpler than the communication through cmd_wait_set and
> cmd_wait_comp.  But simplicity is ultimately subjective and we can
> argue all day.
> 

What I don't like is the endless loop in target_wait_for_sess_cmds()
that acquires and releases ->sess_cmd_lock for every command, with a
hard-coded msleep thrown in.

> 
> 
>  drivers/infiniband/ulp/srpt/ib_srpt.c  |    2 +-
>  drivers/scsi/qla2xxx/tcm_qla2xxx.c     |    2 +-
>  drivers/target/target_core_transport.c |   64 +++++++++-----------------------
>  include/target/target_core_base.h      |    2 -
>  include/target/target_core_fabric.h    |    2 +-
>  5 files changed, 20 insertions(+), 52 deletions(-)
> 
> But diffstat is reasonably objective.  Do you really want me to come
> up with an alternative patch that adds code instead of removing it?
> 

What I want is the part of Roland's commit reverted that introduced the
regression, that started you down this particular path of adding
unnecessary locking to target_wait_for_sess_cmds().

And if your using diffstat as a guide, after re-adding the handful of
parts for ->sess_wait_list from commit 1c7b13fe6 plus removing the dead
code in target_wait_for_sess_cmds(), the number of changed lines will
still be a net minus.

--nab

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