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Message-ID: <20201120140819.GA7359@redhat.com>
Date: Fri, 20 Nov 2020 09:08:20 -0500
From: Mike Snitzer <snitzer@...hat.com>
To: Mikulas Patocka <mpatocka@...hat.com>
Cc: Randy Dunlap <rdunlap@...radead.org>,
Christian Borntraeger <borntraeger@...ibm.com>,
linux-kernel@...r.kernel.org, Alasdair Kergon <agk@...hat.com>,
dm-devel@...hat.com, Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>, linux-s390@...r.kernel.org
Subject: Re: md: dm-writeback: add __noreturn to BUG-ging function
On Wed, Nov 18 2020 at 4:24pm -0500,
Mikulas Patocka <mpatocka@...hat.com> wrote:
>
>
> On Wed, 18 Nov 2020, Mike Snitzer wrote:
>
> > On Wed, Nov 18 2020 at 10:49am -0500,
> > Mike Snitzer <snitzer@...hat.com> wrote:
> >
> > > I don't think my suggestion will help.. given it'd still leave
> > > persistent_memory_claim() without a return statement.
> > >
> > > Think it worthwhile to just add a dummy 'return 0;' after the BUG().
> >
> > Decided to go with this, now staged for 5.11:
> > https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-5.11&id=a1e4865b4dda7071f3707f7e551289ead66e38b1
>
> Hi
>
> I would just use "return -EOPNOTSUPP;" and drop the "#ifdef
> DM_WRITECACHE_HAS_PMEM" that you added.
>
> That BUG/return -EOPNOTSUPP code can't happen at all - if
> DM_WRITECACHE_HAS_PMEM is not defined, WC_MODE_PMEM(wc) always returns
> false - so persistent_memory_claim and BUG() can't ever be called. And if
> it can't be called, you don't need to add a code that prints an error in
> that case.
>
> If we don't have DM_WRITECACHE_HAS_PMEM, the compiler optimizer will
> remove all the code guarded with if (WC_MODE_PMEM(wc)) as unreachable.
>
> Mikulas
Fair enough.
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