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Sat, 22 Jul 2023 20:35:56 -0700 (PDT) MIME-Version: 1.0 References: <20230722231508.1030269-1-pasha.tatashin@soleen.com> <20230722231508.1030269-2-pasha.tatashin@soleen.com> In-Reply-To: From: Pasha Tatashin Date: Sat, 22 Jul 2023 23:35:12 -0400 Message-ID: Subject: Re: [PATCH v2 1/3] mm/page_table_check: Do WARN_ON instead of BUG_ON To: Matthew Wilcox Cc: akpm@linux-foundation.org, corbet@lwn.net, linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, rick.p.edgecombe@intel.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 9185A100011 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 7ayewpdjsokeyi5ho1yt5agzpxezwtat X-HE-Tag: 1690083357-936629 X-HE-Meta: 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 L8oULgcY FaNqP1y7B9NFcK3uXVK7H/nueyY93xo5/tBiBa5PQ8is6jt/B8PWwOSa2JmZxp5rEcgHR0C3raTsl3YvHMA6zw94zox/5qNY8O2h9raCfYad2w7U6s16wjKU/vNrwc3Q1eV67y7ZghlOoj3vCmF39Jeb/Ty/qJTqADumkLBZjDYQB9i8vEVkQxAaib/Pr4tFTyu0aZaFd6fCotWXDegdH/BrQ3UpolMJ9JDgz6LIaENudLuxxOveQPdV2LxWUepE6uNpbj+C1hAVx5DeggVltkVKCD0cRRi+puuNMacfcVPsbN8BZJTL3PJhJSw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Jul 22, 2023 at 9:56=E2=80=AFPM Matthew Wilcox wrote: > > On Sat, Jul 22, 2023 at 11:15:06PM +0000, Pasha Tatashin wrote: > > static struct page_table_check *get_page_table_check(struct page_ext *= page_ext) > > { > > - BUG_ON(!page_ext); > > + PAGE_TABLE_CHECK_WARN(!page_ext); > > + > > return (void *)(page_ext) + page_table_check_ops.offset; > > } > > [...] > > > @@ -137,15 +144,15 @@ void __page_table_check_zero(struct page *page, u= nsigned int order) > > struct page_ext *page_ext; > > unsigned long i; > > > > - BUG_ON(PageSlab(page)); > > + PAGE_TABLE_CHECK_WARN(PageSlab(page)); > > > > page_ext =3D page_ext_get(page); > > - BUG_ON(!page_ext); > > + PAGE_TABLE_CHECK_WARN(!page_ext); > > for (i =3D 0; i < (1ul << order); i++) { > > struct page_table_check *ptc =3D get_page_table_check(pag= e_ext); > > Seems like we're going to warn about !page_ext twice? Or more than > twice -- once per tail page? > > But then we'll crash because page_ext was NULL and offset was small? Good catch, page_ext should not be NULL, yet I do not want to add BUG_ON, let me fix this by warning and gracefully returning if page_ext is NULL Pasha