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[213.151.95.130]) by smtp.gmail.com with ESMTPSA id v3sm47402669wru.32.2020.01.20.06.07.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Jan 2020 06:07:41 -0800 (PST) Date: Mon, 20 Jan 2020 15:07:40 +0100 From: Michal Hocko To: Qian Cai Cc: akpm@linux-foundation.org, david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -mm v2] mm/page_isolation: fix potential warning from user Message-ID: <20200120140740.GG18451@dhcp22.suse.cz> References: <20200120131909.813-1-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200120131909.813-1-cai@lca.pw> User-Agent: Mutt/1.12.2 (2019-09-21) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 20-01-20 08:19:09, Qian Cai wrote: > It makes sense to call the WARN_ON_ONCE(zone_idx(zone) == 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. Let's just make it clear that this mostly a pre-cautious because a real DoS should be pretty much impossible. But let's see whether somebody want to make a CVE out of it ;) > 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. > > Suggested-by: Michal Hocko > Signed-off-by: Qian Cai Acked-by: Michal Hocko Thanks! > --- > > v2: Improve the commit log. > Warn for all start_isolate_page_range() users not just offlining. > > mm/page_alloc.c | 11 ++++------- > mm/page_isolation.c | 30 +++++++++++++++++------------- > 2 files changed, 21 insertions(+), 20 deletions(-) > > 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; > > - goto unmovable; > + return page; > } > > for (; iter < pageblock_nr_pages; iter++) { > @@ -8241,7 +8241,7 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page, > page = pfn_to_page(pfn + iter); > > if (PageReserved(page)) > - goto unmovable; > + return page; > > /* > * 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; > > if (!hugepage_migration_supported(page_hstate(head))) > - goto unmovable; > + return page; > > skip_pages = compound_nr(head) - (page - head); > iter += 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) == ZONE_MOVABLE); > - return pfn_to_page(pfn + iter); > } > > #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 > > -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) > { > - struct page *unmovable = NULL; > + struct page *unmovable = ERR_PTR(-EBUSY); > struct zone *zone; > unsigned long flags; > - int ret = -EBUSY; > > zone = page_zone(page); > > @@ -49,21 +49,25 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_ > NULL); > > __mod_zone_freepage_state(zone, -nr_pages, mt); > - ret = 0; > } > > 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) == ZONE_MOVABLE); > + > + if ((isol_flags & REPORT_FAILURE) && !IS_ERR(unmovable)) > + /* > + * printk() with zone->lock held will likely trigger a > + * lockdep splat, so defer it here. > + */ > + dump_page(unmovable, "unmovable page"); > + } > + > + return !!unmovable; > } > > static void unset_migratetype_isolate(struct page *page, unsigned migratetype) > -- > 2.21.0 (Apple Git-122.2) -- Michal Hocko SUSE Labs