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[66.187.233.206]) by smtp.gmail.com with ESMTPSA id d25sm3252655qtq.11.2020.02.14.06.30.27 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Feb 2020 06:30:28 -0800 (PST) Message-ID: <1581690626.7365.61.camel@lca.pw> Subject: Re: [PATCH -next v2] mm: annotate a data race in page_zonenum() From: Qian Cai To: paulmck@kernel.org Cc: akpm@linux-foundation.org, elver@google.com, david@redhat.com, jack@suse.cz, jhubbard@nvidia.com, ira.weiny@intel.com, dan.j.williams@intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Date: Fri, 14 Feb 2020 09:30:26 -0500 In-Reply-To: <20200213192659.GJ2935@paulmck-ThinkPad-P72> References: <1581619089-14472-1-git-send-email-cai@lca.pw> <20200213192659.GJ2935@paulmck-ThinkPad-P72> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.22.6 (3.22.6-10.el7) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit 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 Thu, 2020-02-13 at 11:26 -0800, Paul E. McKenney wrote: > On Thu, Feb 13, 2020 at 01:38:09PM -0500, Qian Cai wrote: > > BUG: KCSAN: data-race in page_cpupid_xchg_last / put_page > > > > write (marked) to 0xfffffc0d48ec1a00 of 8 bytes by task 91442 on cpu 3: > > page_cpupid_xchg_last+0x51/0x80 > > page_cpupid_xchg_last at mm/mmzone.c:109 (discriminator 11) > > wp_page_reuse+0x3e/0xc0 > > wp_page_reuse at mm/memory.c:2453 > > do_wp_page+0x472/0x7b0 > > do_wp_page at mm/memory.c:2798 > > __handle_mm_fault+0xcb0/0xd00 > > handle_pte_fault at mm/memory.c:4049 > > (inlined by) __handle_mm_fault at mm/memory.c:4163 > > handle_mm_fault+0xfc/0x2f0 > > handle_mm_fault at mm/memory.c:4200 > > do_page_fault+0x263/0x6f9 > > do_user_addr_fault at arch/x86/mm/fault.c:1465 > > (inlined by) do_page_fault at arch/x86/mm/fault.c:1539 > > page_fault+0x34/0x40 > > > > read to 0xfffffc0d48ec1a00 of 8 bytes by task 94817 on cpu 69: > > put_page+0x15a/0x1f0 > > page_zonenum at include/linux/mm.h:923 > > (inlined by) is_zone_device_page at include/linux/mm.h:929 > > (inlined by) page_is_devmap_managed at include/linux/mm.h:948 > > (inlined by) put_page at include/linux/mm.h:1023 > > wp_page_copy+0x571/0x930 > > wp_page_copy at mm/memory.c:2615 > > do_wp_page+0x107/0x7b0 > > __handle_mm_fault+0xcb0/0xd00 > > handle_mm_fault+0xfc/0x2f0 > > do_page_fault+0x263/0x6f9 > > page_fault+0x34/0x40 > > > > Reported by Kernel Concurrency Sanitizer on: > > CPU: 69 PID: 94817 Comm: systemd-udevd Tainted: G W O L 5.5.0-next-20200204+ #6 > > Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 > > > > A page never changes its zone number. The zone number happens to be > > stored in the same word as other bits which are modified, but the zone > > number bits will never be modified by any other write, so it can accept > > a reload of the zone bits after an intervening write and it don't need > > to use READ_ONCE(). Thus, annotate this data race using > > ASSERT_EXCLUSIVE_BITS() to also assert that there are no concurrent > > writes to it. > > > > Suggested-by: Marco Elver > > Signed-off-by: Qian Cai > > --- > > > > v2: use ASSERT_EXCLUSIVE_BITS(). > > > > BTW, not sure if it is easier for Andrew with Paul to pick this up (with > > Andrew's ACK), since ASSERT_EXCLUSIVE_BITS() is in -rcu tree only (or likely > > tomorrow's -next tree). > > Here are the options I know of, any of which work for me: > > 1. I take the patch given appropriate acks/reviews. > > 2. Someone hangs onto the patch until the KCSAN infrastructure > hits mainline and then sends it up via whatever path. > > 3. One way to do #2 is to merge the -rcu tree's "kcsan" branch and > then queue this patch on top of that, again sending this patch > along once KCSAN hits mainline. Unusually for the -rcu tree, > the "kcsan" branch is not supposed to be rebased. > > Either way, just let me know! I suppose it is up to Andrew what he prefers. I may have another pile of patches depends on some of those KCSAN things (except the data_race() macro) are coming, so I'd like to find a way to get into -next first rather than waiting to send them in April (once KCSAN hit the mainline) if possible. > > Thanx, Paul > > > include/linux/mm.h | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 52269e56c514..0d70fafd055c 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -920,6 +920,7 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg, > > > > static inline enum zone_type page_zonenum(const struct page *page) > > { > > + ASSERT_EXCLUSIVE_BITS(page->flags, ZONES_MASK << ZONES_PGSHIFT); > > return (page->flags >> ZONES_PGSHIFT) & ZONES_MASK; > > } > > > > -- > > 1.8.3.1 > >