linux-kernel - Re: [PATCH 2/2] target: remove spin_lock_assert() in __target_(attach|detach)_tg_pt

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Message-ID: <1521827753.2535.18.camel@wdc.com>
Date:   Fri, 23 Mar 2018 17:55:54 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "bigeasy@...utronix.de" <bigeasy@...utronix.de>
CC:     "daniel@...stot.me" <daniel@...stot.me>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "nab@...ux-iscsi.org" <nab@...ux-iscsi.org>,
        "acme@...nel.org" <acme@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "williams@...hat.com" <williams@...hat.com>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "lclaudio@...hat.com" <lclaudio@...hat.com>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH 2/2] target: remove spin_lock_assert() in
 __target_(attach|detach)_tg_pt_gp()

On Fri, 2018-03-23 at 18:50 +0100, bigeasy@...utronix.de wrote:
> On 2018-03-23 17:44:46 [+0000], Bart Van Assche wrote:
> > In other words, do we really need to remove these checks? I think that these
> > checks are useful as documentation to people who read the SCSI target code.
> > The target code is already hard to follow so I think any documentation,
> > especially documentation in the form of code that is checked at runtime, is
> > welcome.
> 
> so if I remove those two and add a kernel doc comment instead, saying
> that the caller needs to ensure that "lun->lun_tg_pt_gp_lock" is held
> then we would remove the obvious runtime check and add a piece of
> documentation. Would that work?

Comments are not verified at runtime and hence can become outdated if the code
is modified. assert_spin_locked() and lockdep_assert_held() assertions however
are verified at runtime with the proper kernel configuration options enabled.
Hence my preference for assert_spin_locked()/lockdep_assert_held() over source
code comments.

Thanks,

Bart.