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From:   "Fabio M. De Francesco" <fmdefrancesco@gmail.com>
To:     Ira Weiny <ira.weiny@intel.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Peter Collingbourne <pcc@google.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] mm/highmem: VM_BUG_ON() if offset + len > PAGE_SIZE
Date:   Mon, 25 Apr 2022 22:05:29 +0200
Message-ID: <2701286.BEx9A2HvPv@leap>
In-Reply-To: <YmbQluz5i95fkhn9@iweiny-desk3>
References: <20220424104806.25396-1-fmdefrancesco@gmail.com> <8929547.CDJkKcVGEf@leap> <YmbQluz5i95fkhn9@iweiny-desk3>
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On luned=C3=AC 25 aprile 2022 18:47:18 CEST Ira Weiny wrote:
> On Mon, Apr 25, 2022 at 03:47:38AM +0200, Fabio M. De Francesco wrote:
> > On domenica 24 aprile 2022 12:48:06 CEST Fabio M. De Francesco wrote:
> > > Call VM_BUG_ON() if offset + len > PAGE_SIZE.
> > >=20
> > > This is an RFC patch because I'm not sure if we actually need to=20
> > BUG_ON(),
> >=20
> > Actually I considered VM_BUG_ON() for consistency with the other=20
functions=20
> > in highmem.h
> >=20
> > What about VM_WARN_ON_ONCE() here and also in memset_page?
>=20
> For consistency leave this as a VM_BUG_ON[1]
>=20
> I've been down a similar path[2] and there was a long discussion about=20
it.[3]
>=20
> In the end we settled on VM_BUG_ON.[4]

Thanks for your reply and for providing so many helpful links :)

I just read the ones related to VM_BUG_ON() (I don't have time for=20
flush_dcache_page() today). Since the consensus for these kinds of issues=20
is in favor of using VM_BUG_ON(), that's OK for me.

I will send a "real" patch by tomorrow.

Again, thanks,

=46abio

> As to the addition of flush_dcache_page().  There was a discussion here.
>=20
> https://lore.kernel.org/lkml/CAHk-=3DwiKac4t-fOP_3fAf7nETfFLhT3ShmRmBq2J9=
6y6jAr56Q@mail.gmail.com/
>=20
> Ira
>=20
> [1] https://lore.kernel.org/lkml/20210209205249.GB2975576@iweiny-DESK2.sc=
=2Eintel.com/
>=20
> [2] https://lore.kernel.org/lkml/20201209022250.GP1563847@iweiny-DESK2.sc=
=2Eintel.com/
>=20
> [3] https://lore.kernel.org/lkml/20201208213255.GO1563847@iweiny-DESK2.sc=
=2Eintel.com/
>=20
> [4] https://lore.kernel.org/lkml/20210210174928.3156073-1-ira.weiny@intel=
=2Ecom/