From: Greg KH <gregkh@linuxfoundation.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Luis Chamberlain <mcgrof@kernel.org>,
Minchan Kim <minchan@kernel.org>,
keescook@chromium.org, dhowells@redhat.com, hch@infradead.org,
mbenes@suse.com, ngupta@vflare.org,
sergey.senozhatsky.work@gmail.com, axboe@kernel.dk,
linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] zram: fix crashes due to use of cpu hotplug multistate
Date: Thu, 8 Apr 2021 08:16:06 +0200 [thread overview]
Message-ID: <YG6fpgmYSg/PwOrU@kroah.com> (raw)
In-Reply-To: <87blap4kum.ffs@nanos.tec.linutronix.de>
On Thu, Apr 08, 2021 at 03:37:53AM +0200, Thomas Gleixner wrote:
> Greg,
>
> On Fri, Apr 02 2021 at 09:54, Greg KH wrote:
> > On Thu, Apr 01, 2021 at 11:59:25PM +0000, Luis Chamberlain wrote:
> >> As for the syfs deadlock possible with drivers, this fixes it in a generic way:
> >>
> >> commit fac43d8025727a74f80a183cc5eb74ed902a5d14
> >> Author: Luis Chamberlain <mcgrof@kernel.org>
> >> Date: Sat Mar 27 14:58:15 2021 +0000
> >>
> >> sysfs: add optional module_owner to attribute
> >>
> >> This is needed as otherwise the owner of the attribute
> >> or group read/store might have a shared lock used on driver removal,
> >> and deadlock if we race with driver removal.
> >>
> >> Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
> >
> > No, please no. Module removal is a "best effort", if the system dies
> > when it happens, that's on you. I am not willing to expend extra energy
> > and maintance of core things like sysfs for stuff like this that does
> > not matter in any system other than a developer's box.
> >
> > Lock data, not code please. Trying to tie data structure's lifespans
> > to the lifespan of code is a tangled mess, and one that I do not want to
> > add to in any form.
> >
> > sorry,
>
> Sorry, but you are fundamentaly off track here. This has absolutely
> nothing to do with module removal.
>
> The point is that module removal is the reverse operation of module
> insertion. So far so good.
>
> But module insertion can fail. So if you have nested functionalities
> which hang off or are enabled by moduled insertion then any fail in that
> sequence has to be able to roll back and clean up properly no matter
> what.
>
> Which it turn makes modules removal a reverse operation of module
> insertion.
>
> If you think otherwise, then please provide a proper plan how nested
> operations like sysfs - not to talk about more complex things like multi
> instance discovery which can happen inside a module insertion sequence
> can be properly rolled back.
>
> Just declaring that rmmod is evil does not cut it. rmmod is the least of
> the problems. If that fails, then a lot of rollback, failure handling
> mechanisms are missing in the setup path already.
>
> Anything which cannot cleanly rollback no matter whether the fail or
> rollback request happens at insertion time or later is broken by design.
>
> So either you declare module removal as disfunctional or you stop making
> up semantically ill defined and therefore useless claims about it.
>
> Your argument in:
>
> https://lore.kernel.org/linux-block/YGbNpLKXfWpy0ZZa@kroah.com/
>
> "Lock data, not code please. Trying to tie data structure's lifespans
> to the lifespan of code is a tangled mess, and one that I do not want to
> add to in any form"
>
> is just useless blurb because the fundamental purpose of discovery code
> is to create the data structures which are tied to the code which is
> associated to it.
>
> Please stop this 'module removal' is not supported nonsense unless you
> can prove a complete indepenence of module init/discovery code to
> subsequent discovered entities depending on it.
Ok, but to be fair, trying to add the crazy hacks that were being
proposed to sysfs for something that is obviously not a code path that
can be taken by a normal user or operation is just not going to fly.
Removing a module from a system has always been "let's try it and see!"
type of operation for a very long time. While we try our best, doing
horrible hacks for this rare type of thing are generally not considered
a good idea which is why I said that.
thanks,
greg k-h
next prev parent reply other threads:[~2021-04-08 6:16 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-06 2:20 [PATCH 0/2] zram: fix few ltp zram02.sh crashes Luis Chamberlain
2021-03-06 2:20 ` [PATCH 1/2] zram: fix crashes due to use of cpu hotplug multistate Luis Chamberlain
2021-03-09 2:55 ` Minchan Kim
2021-03-10 13:11 ` Luis Chamberlain
2021-03-10 21:25 ` Luis Chamberlain
2021-03-12 2:08 ` Minchan Kim
2021-03-10 21:21 ` Luis Chamberlain
2021-03-12 2:14 ` Minchan Kim
2021-03-12 18:32 ` Luis Chamberlain
2021-03-12 19:28 ` Minchan Kim
2021-03-19 19:09 ` Luis Chamberlain
2021-03-22 16:37 ` Minchan Kim
2021-03-22 20:41 ` Luis Chamberlain
2021-03-22 22:12 ` Minchan Kim
2021-04-01 23:59 ` Luis Chamberlain
2021-04-02 7:54 ` Greg KH
2021-04-02 18:30 ` Luis Chamberlain
2021-04-03 6:13 ` Greg KH
[not found] ` <20210406003152.GZ4332@42.do-not-panic.com>
2021-04-06 12:00 ` Miroslav Benes
2021-04-06 15:54 ` Josh Poimboeuf
2021-04-07 14:09 ` Peter Zijlstra
2021-04-07 15:30 ` Josh Poimboeuf
2021-04-07 16:48 ` Peter Zijlstra
2021-04-07 20:17 ` Josh Poimboeuf
2021-04-08 6:18 ` Greg KH
2021-04-08 13:16 ` Steven Rostedt
2021-04-08 13:37 ` Josh Poimboeuf
2021-04-08 1:37 ` Thomas Gleixner
2021-04-08 6:16 ` Greg KH [this message]
2021-04-08 8:01 ` Jiri Kosina
2021-04-08 8:09 ` Greg KH
2021-04-08 8:35 ` Jiri Kosina
2021-04-08 8:55 ` Greg KH
2021-04-08 18:40 ` Luis Chamberlain
2021-04-09 3:01 ` Kees Cook
2021-04-05 17:07 ` Minchan Kim
2021-04-05 19:00 ` Luis Chamberlain
2021-04-05 19:58 ` Minchan Kim
2021-04-06 0:29 ` Luis Chamberlain
2021-04-07 1:23 ` Minchan Kim
2021-04-07 1:38 ` Minchan Kim
2021-04-07 14:52 ` Luis Chamberlain
2021-04-07 14:50 ` Luis Chamberlain
2021-03-06 2:20 ` [PATCH 2/2] zram: fix races of sysfs attribute removal and usage Luis Chamberlain
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