linux-kernel - Re: LVM snapshot broke between 4.14 and 4.16

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Date:   Sat, 4 Aug 2018 14:19:51 -0400
From:   Mike Snitzer <snitzer@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     wgh@...lan.ru, Theodore Ts'o <tytso@....edu>,
        Jens Axboe <axboe@...nel.dk>, Sagi Grimberg <sagi@...mberg.me>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>, dm-devel@...hat.com,
        Ilya Dryomov <idryomov@...il.com>,
        Zdenek Kabelac <zkabelac@...hat.com>
Subject: Re: LVM snapshot broke between 4.14 and 4.16

On Sat, Aug 04 2018 at  1:04pm -0400,
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Sat, Aug 4, 2018 at 3:03 AM WGH <wgh@...lan.ru> wrote:
> >
> > >
> > The patch works for me.
> >
> > However, there's no text messsage in the kernel log, just a traceback. I
> > think that's because WARN_ONCE is supposed to take condition as a first
> > argument.
> 
> Duh.
> 
> It needs to be WARN_ONCE(1, ...);
> 
> I obviously didn't test that patch, but I _did_ compile it. I wonder
> why I didn't get a compiler warning for it...
> 
> [ Goes off and looks ]
> 
> Oh, because the "bio_devname(bio, b)" argument ended up being
> interpreted as the format string, and since it was a dynamic string
> the compiler felt it was all fine. Just bad luck.
> 
> Anyway, just out of curiosity, what was the traceback?
> 
> I'm not entirely happy with that patch either (even after the obvious
> fix to add the "1" argument), but it does seem like the minimal
> temporary workaround for now.

I agree.

Please feel free to add my:

Acked-by: Mike Snitzer <snitzer@...hat.com>