linux-kernel - Re: [PATCH v2 01/11] pstore/blk: new support logger for block devices

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Date:   Fri, 20 Mar 2020 11:20:22 -0700
From:   Kees Cook <keescook@...omium.org>
To:     WeiXiong Liao <liaoweixiong@...winnertech.com>
Cc:     Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mtd@...ts.infradead.org
Subject: Re: [PATCH v2 01/11] pstore/blk: new support logger for block devices

On Fri, Mar 20, 2020 at 09:50:36AM +0800, WeiXiong Liao wrote:
> On 2020/3/19 AM 1:23, Kees Cook wrote:
> > On Thu, Feb 27, 2020 at 04:21:51PM +0800, liaoweixiong wrote:
> >> On 2020/2/26 AM 8:52, Kees Cook wrote:
> >>> On Fri, Feb 07, 2020 at 08:25:45PM +0800, WeiXiong Liao wrote:
> >>>> +obj-$(CONFIG_PSTORE_BLK) += pstore_blk.o
> >>>> +pstore_blk-y += blkzone.o
> >>>
> >>> Why this dance with files? I would just expect:
> >>>
> >>> obj-$(CONFIG_PSTORE_BLK)     += blkzone.o
> >>>
> >>
> >> This makes the built module named blkzone.ko rather than
> >> pstore_blk.ko.
> > 
> > You can just do a regular build rule:
> > 
> > obj-$(CONFIG_PSTORE_BLK) += blkzone.o
> > 
> 
> I don't get it. If make it as your words, the built module will be
> blkzone.ko.
> The module is named pstore/blk, however it built out blkzone.ko. I think
> it's confusing.

I mean just pick whatever filename you want it to be named. The Makefile
case for ramoops was that ramoops got renamed but we wanted to keep the
old API name.

So, if you want it named pstore-blk.ko, just rename blkzone.c to
pstore-blk.c.

> >>> If you're expecting concurrent writers (use of atomic_set(), I would
> >>> expect the whole write to be locked instead. (i.e. what happens if
> >>> multiple callers call blkz_zone_write()?)
> >>>
> >>
> >> I don't agree with it. The datalen will be updated everywhere. It's useless
> >> to lock here.
> > 
> > But there could be multiple writers; locking should be needed.
> > 
> 
> All the recorders such as dmesg, pmsg, console and ftrace have been
> locked on
> pstore and upper layers. So, a recorder will not write in parallel and
> different
> recorders operate privately zone. They don't have any influence on each
> other.

Yes, sorry, I was confusing myself about pmsg, and I forgot it had a
global lock. Each are locked or split by CPU.

> The only parallel case I think is that recorder writes while dirty-flush
> thread is
> working. And the dirty-flusher will flush the whole zone rather than
> part of it, so,
> it is OK to call in parallel.

Okay, thanks for clarifying.

> Based on these reasons, I don't think locking should be needed.

Agreed.

-- 
Kees Cook