linux-kernel - Re: [PATCH -next v2] mm: annotate a data race in page

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Date:   Wed, 19 Feb 2020 16:55:40 -0500
From:   Qian Cai <cai@....pw>
To:     akpm@...ux-foundation.org
Cc:     John Hubbard <jhubbard@...dia.com>, paulmck@...nel.org,
        elver@...gle.com, david@...hat.com, jack@...e.cz,
        ira.weiny@...el.com, dan.j.williams@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next v2] mm: annotate a data race in page_zonenum()

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@...gle.com>
> > Signed-off-by: Qian Cai <cai@....pw>
> > ---
> > 
> > v2: use ASSERT_EXCLUSIVE_BITS().
> 
> 
> Much cleaner, thanks to this new macro. You can add:
> 
> 
>     Reviewed-by: John Hubbard <jhubbard@...dia.com>
> 
> 
> thanks,