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[71.184.117.43]) by smtp.gmail.com with ESMTPSA id f19sm15659723qkk.69.2020.01.20.05.56.47 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 20 Jan 2020 05:56:47 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.0 \(3608.40.2.2.4\)) Subject: Re: [PATCH -mm v2] mm/page_isolation: fix potential warning from user From: Qian Cai In-Reply-To: Date: Mon, 20 Jan 2020 08:56:46 -0500 Cc: Andrew Morton , mhocko@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <96675869-3815-4E98-8492-1D84F5B42AED@lca.pw> References: <20200120131909.813-1-cai@lca.pw> <8c56268d-9b8a-f62e-eca9-7707852a2aaf@redhat.com> To: David Hildenbrand X-Mailer: Apple Mail (2.3608.40.2.2.4) 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 Jan 20, 2020, at 8:38 AM, David Hildenbrand = wrote: >=20 > On 20.01.20 14:30, David Hildenbrand wrote: >> On 20.01.20 14:19, Qian Cai wrote: >>> It makes sense to call the WARN_ON_ONCE(zone_idx(zone) =3D=3D = ZONE_MOVABLE) >>> from start_isolate_page_range(), but should avoid triggering it from >>> userspace, i.e, from is_mem_section_removable() because it could be = a >>> DoS if warn_on_panic is set. >>>=20 >>> While at it, simplify the code a bit by removing an unnecessary jump >>> label and a local variable, so set_migratetype_isolate() could = really >>> return a bool. >>>=20 >>> Suggested-by: Michal Hocko >>> Signed-off-by: Qian Cai >>> --- >>>=20 >>> v2: Improve the commit log. >>> Warn for all start_isolate_page_range() users not just offlining. >>>=20 >>> mm/page_alloc.c | 11 ++++------- >>> mm/page_isolation.c | 30 +++++++++++++++++------------- >>> 2 files changed, 21 insertions(+), 20 deletions(-) >>>=20 >>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >>> index 621716a25639..3c4eb750a199 100644 >>> --- a/mm/page_alloc.c >>> +++ b/mm/page_alloc.c >>> @@ -8231,7 +8231,7 @@ struct page *has_unmovable_pages(struct zone = *zone, struct page *page, >>> if (is_migrate_cma(migratetype)) >>> return NULL; >>>=20 >>> - goto unmovable; >>> + return page; >>> } >>>=20 >>> for (; iter < pageblock_nr_pages; iter++) { >>> @@ -8241,7 +8241,7 @@ struct page *has_unmovable_pages(struct zone = *zone, struct page *page, >>> page =3D pfn_to_page(pfn + iter); >>>=20 >>> if (PageReserved(page)) >>> - goto unmovable; >>> + return page; >>>=20 >>> /* >>> * If the zone is movable and we have ruled out all = reserved >>> @@ -8261,7 +8261,7 @@ struct page *has_unmovable_pages(struct zone = *zone, struct page *page, >>> unsigned int skip_pages; >>>=20 >>> if = (!hugepage_migration_supported(page_hstate(head))) >>> - goto unmovable; >>> + return page; >>>=20 >>> skip_pages =3D compound_nr(head) - (page - = head); >>> iter +=3D skip_pages - 1; >>> @@ -8303,12 +8303,9 @@ struct page *has_unmovable_pages(struct zone = *zone, struct page *page, >>> * is set to both of a memory hole page and a _used_ = kernel >>> * page at boot. >>> */ >>> - goto unmovable; >>> + return page; >>> } >>> return NULL; >>> -unmovable: >>> - WARN_ON_ONCE(zone_idx(zone) =3D=3D ZONE_MOVABLE); >>> - return pfn_to_page(pfn + iter); >>> } >>>=20 >>> #ifdef CONFIG_CONTIG_ALLOC >>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >>> index e70586523ca3..31f5516f5d54 100644 >>> --- a/mm/page_isolation.c >>> +++ b/mm/page_isolation.c >>> @@ -15,12 +15,12 @@ >>> #define CREATE_TRACE_POINTS >>> #include >>>=20 >>> -static int set_migratetype_isolate(struct page *page, int = migratetype, int isol_flags) >>> +static bool set_migratetype_isolate(struct page *page, int = migratetype, >>> + int isol_flags) >>=20 >> Why this change? >>=20 >>> { >>> - struct page *unmovable =3D NULL; >>> + struct page *unmovable =3D ERR_PTR(-EBUSY); >>=20 >> Also, why this change? >>=20 >>> struct zone *zone; >>> unsigned long flags; >>> - int ret =3D -EBUSY; >>>=20 >>> zone =3D page_zone(page); >>>=20 >>> @@ -49,21 +49,25 @@ static int set_migratetype_isolate(struct page = *page, int migratetype, int isol_ >>> = NULL); >>>=20 >>> __mod_zone_freepage_state(zone, -nr_pages, mt); >>> - ret =3D 0; >>> } >>>=20 >>> out: >>> spin_unlock_irqrestore(&zone->lock, flags); >>> - if (!ret) >>> + >>> + if (!unmovable) { >>> drain_all_pages(zone); >>> - else if ((isol_flags & REPORT_FAILURE) && unmovable) >>> - /* >>> - * printk() with zone->lock held will guarantee to = trigger a >>> - * lockdep splat, so defer it here. >>> - */ >>> - dump_page(unmovable, "unmovable page"); >>> - >>> - return ret; >>> + } else { >>> + WARN_ON_ONCE(zone_idx(zone) =3D=3D ZONE_MOVABLE); >>> + >>> + if ((isol_flags & REPORT_FAILURE) && !IS_ERR(unmovable)) >>> + /* >>=20 >> Why this change? (!IS_ERR) >>=20 >>=20 >> Some things here look unrelated - or I am missing something :) >>=20 >=20 > FWIW, I'd prefer this change without any such cleanups (e.g., I don't > like returning a bool from this function and the IS_ERR handling, = makes > the function harder to read than before) What is Michal or Andrew=E2=80=99s opinion? BTW, a bonus point to return = a bool is that it helps the code robustness in general, as UBSAN will be able = to catch any abuse.