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Date:   Wed, 19 Feb 2020 15:47:52 -0800
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Qian Cai <cai@lca.pw>
Cc:     akpm@linux-foundation.org, John Hubbard <jhubbard@nvidia.com>,
        elver@google.com, david@redhat.com, jack@suse.cz,
        ira.weiny@intel.com, dan.j.williams@intel.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH -next v2] mm: annotate a data race in page_zonenum()
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On Wed, Feb 19, 2020 at 04:55:40PM -0500, Qian Cai wrote:
> Andrew, since you had picked the similar one which also depends
> on?ASSERT_EXCLUSIVE_*,?can you pick up this patch as well?
> 
> On Thu, 2020-02-13 at 13:20 -0800, John Hubbard wrote:
> > On 2/13/20 10:38 AM, 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 <elver@google.com>
> > > Signed-off-by: Qian Cai <cai@lca.pw>
> > > ---
> > > 
> > > v2: use ASSERT_EXCLUSIVE_BITS().
> > 
> > 
> > Much cleaner, thanks to this new macro. You can add:
> > 
> > 
> >     Reviewed-by: John Hubbard <jhubbard@nvidia.com>

It looks like Andrew already pulled this one in, but let me know if
he drops it for whatever reason.

							Thanx, Paul