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Subject: Re: [PATCH] mm, numa: fix bad pmd by atomically check for
 pmd_trans_huge when marking page tables prot_numa
From:   Qian Cai <cai@lca.pw>
In-Reply-To: <20200216191800.22423-1-aquini@redhat.com>
Date:   Fri, 6 Mar 2020 21:40:10 -0500
Cc:     Linux Memory Management List <linux-mm@kvack.org>,
        linux-kernel@vger.kernel.org, mgorman@techsingularity.net,
        akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz
Content-Transfer-Encoding: quoted-printable
Message-Id: <2E0766B8-DDD1-4448-8605-8535A16670FC@lca.pw>
References: <20200216191800.22423-1-aquini@redhat.com>
To:     Rafael Aquini <aquini@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Feb 16, 2020, at 2:18 PM, Rafael Aquini <aquini@redhat.com> wrote:
>=20
> From: Mel Gorman <mgorman@techsingularity.net>
>  A user reported a bug against a distribution kernel while running
>  a proprietary workload described as "memory intensive that is not
>  swapping" that is expected to apply to mainline kernels. The workload
>  is read/write/modifying ranges of memory and checking the contents. =
They
>  reported that within a few hours that a bad PMD would be reported =
followed
>  by a memory corruption where expected data was all zeros.  A partial =
report
>  of the bad PMD looked like
>=20
>  [ 5195.338482] ../mm/pgtable-generic.c:33: bad pmd =
ffff8888157ba008(000002e0396009e2)
>  [ 5195.341184] ------------[ cut here ]------------
>  [ 5195.356880] kernel BUG at ../mm/pgtable-generic.c:35!
>  ....
>  [ 5195.410033] Call Trace:
>  [ 5195.410471]  [<ffffffff811bc75d>] =
change_protection_range+0x7dd/0x930
>  [ 5195.410716]  [<ffffffff811d4be8>] change_prot_numa+0x18/0x30
>  [ 5195.410918]  [<ffffffff810adefe>] task_numa_work+0x1fe/0x310
>  [ 5195.411200]  [<ffffffff81098322>] task_work_run+0x72/0x90
>  [ 5195.411246]  [<ffffffff81077139>] exit_to_usermode_loop+0x91/0xc2
>  [ 5195.411494]  [<ffffffff81003a51>] =
prepare_exit_to_usermode+0x31/0x40
>  [ 5195.411739]  [<ffffffff815e56af>] retint_user+0x8/0x10
>=20
>  Decoding revealed that the PMD was a valid prot_numa PMD and the bad =
PMD
>  was a false detection. The bug does not trigger if automatic NUMA =
balancing
>  or transparent huge pages is disabled.
>=20
>  The bug is due a race in change_pmd_range between a pmd_trans_huge =
and
>  pmd_nond_or_clear_bad check without any locks held. During the =
pmd_trans_huge
>  check, a parallel protection update under lock can have cleared the =
PMD
>  and filled it with a prot_numa entry between the transhuge check and =
the
>  pmd_none_or_clear_bad check.
>=20
>  While this could be fixed with heavy locking, it's only necessary to
>  make a copy of the PMD on the stack during change_pmd_range and avoid
>  races. A new helper is created for this as the check if quite subtle =
and the
>  existing similar helpful is not suitable. This passed 154 hours of =
testing
>  (usually triggers between 20 minutes and 24 hours) without detecting =
bad
>  PMDs or corruption. A basic test of an autonuma-intensive workload =
showed
>  no significant change in behaviour.
>=20
> Although Mel withdrew the patch on the face of LKML comment =
https://lkml.org/lkml/2017/4/10/922
> the race window aforementioned is still open, and we have reports of =
Linpack test reporting bad
> residuals after the bad PMD warning is observed. In addition to that, =
bad rss-counter and
> non-zero pgtables assertions are triggered on mm teardown for the task =
hitting the bad PMD.
>=20
> host kernel: mm/pgtable-generic.c:40: bad pmd =
00000000b3152f68(8000000d2d2008e7)
> ....
> host kernel: BUG: Bad rss-counter state mm:00000000b583043d idx:1 =
val:512
> host kernel: BUG: non-zero pgtables_bytes on freeing mm: 4096
>=20
> The issue is observed on a v4.18-based distribution kernel, but the =
race window is
> expected to be applicable to mainline kernels, as well.

After reverted this patch, it is no longer possible to reproduce a bug =
under memory pressure
with swapping on linux-next 20200306,

The trace is a bit off for some reasons, but it is basically,

kernel BUG at include/linux/page-flags.h:317!

end_swap_bio_write()
   SetPageError(page)
       VM_BUG_ON_PAGE(1 && PageCompound(page))=20

The page was allocated in,

do_huge_pmd_anonymous_page()

[ 9598.551238][  T794] oom_reaper: reaped process 49120 (oom02), now =
anon-rss:0kB, file-rss:0kB, shmem-rss:0kB=20
[ 9690.896638][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc0000 =
flags=3D0x0010]=20
[ 9690.910129][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc1000 =
flags=3D0x0010]=20
[ 9690.923933][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc1900 =
flags=3D0x0010]=20
[ 9690.937669][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc1d00 =
flags=3D0x0010]=20
[ 9690.951468][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc2000 =
flags=3D0x0010]=20
[ 9690.964803][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc2400 =
flags=3D0x0010]=20
[ 9690.978256][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc2800 =
flags=3D0x0010]=20
[ 9690.991423][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc2c00 =
flags=3D0x0010]=20
[ 9691.004294][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc3000 =
flags=3D0x0010]=20
[ 9691.017228][  T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged =
[IO_PAGE_FAULT domain=3D0x0027 address=3D0xffffffffffcc3400 =
flags=3D0x0010]=20
[ 9691.029804][  T814] AMD-Vi: Event logged [IO_PAGE_FAULT =
device=3D23:00.0 domain=3D0x0027 address=3D0xffffffffffcc3800 =
flags=3D0x0010]=20
[ 9691.041623][  T814] AMD-Vi: Event logged [IO_PAGE_FAULT =
device=3D23:00.0 domain=3D0x0027 address=3D0xffffffffffcc3c00 =
flags=3D0x0010]=20
[ 9692.767064][    C8] smartpqi 0000:23:00.0: controller is offline: =
status code 0x14803=20
[ 9692.775562][    C8] smartpqi 0000:23:00.0: controller offline=20
[ 9692.841721][   C36] sd 0:1:0:0: [sda] tag#693 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.841970][   C87] blk_update_request: I/O error, dev sda, sector =
59046400 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.842718][   C31] blk_update_request: I/O error, dev sda, sector =
36509696 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.842748][   C18] sd 0:1:0:0: [sda] tag#616 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.842757][   C28] sd 0:1:0:0: [sda] tag#841 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.842766][  C109] sd 0:1:0:0: [sda] tag#393 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.842811][  C109] sd 0:1:0:0: [sda] tag#393 CDB: opcode=3D0x2a 2a =
00 01 60 c8 00 00 02 00 00=20
[ 9692.842840][   C13] sd 0:1:0:0: [sda] tag#324 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.842924][   C18] sd 0:1:0:0: [sda] tag#616 CDB: opcode=3D0x2a 2a =
00 01 c7 8c 00 00 02 00 00=20
[ 9692.842932][  C109] blk_update_request: I/O error, dev sda, sector =
23119872 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.842938][   C28] sd 0:1:0:0: [sda] tag#841 CDB: opcode=3D0x2a 2a =
00 03 2f cc 00 00 02 00 00=20
[ 9692.842984][  T213] sd 0:1:0:0: [sda] tag#47 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.842995][   C28] blk_update_request: I/O error, dev sda, sector =
53464064 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.843000][   C81] sd 0:1:0:0: [sda] tag#10 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.843031][   C18] blk_update_request: I/O error, dev sda, sector =
29854720 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.843056][   C13] sd 0:1:0:0: [sda] tag#324 CDB: opcode=3D0x2a 2a =
00 03 17 66 00 00 02 00 00=20
[ 9692.843101][   C81] sd 0:1:0:0: [sda] tag#10 CDB: opcode=3D0x2a 2a 00 =
00 52 a4 00 00 02 00 00=20
[ 9692.843129][   C13] blk_update_request: I/O error, dev sda, sector =
51865088 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.843192][   C81] blk_update_request: I/O error, dev sda, sector =
5415936 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.843338][  T213] sd 0:1:0:0: [sda] tag#47 CDB: opcode=3D0x2a 2a 00 =
02 be 5a 00 00 02 00 00=20
[ 9692.843358][   C13] sd 0:1:0:0: [sda] tag#325 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.843480][  T213] blk_update_request: I/O error, dev sda, sector =
46029312 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.843485][   C13] sd 0:1:0:0: [sda] tag#325 CDB: opcode=3D0x2a 2a =
00 03 17 68 00 00 02 00 00=20
[ 9692.843510][   C13] blk_update_request: I/O error, dev sda, sector =
51865600 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.843685][  C103] blk_update_request: I/O error, dev sda, sector =
34941952 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0=20
[ 9692.843725][   C96] sd 0:1:0:0: [sda] tag#877 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.843744][   C92] Write-error on swap-device (254:1:39256632)=20
[ 9692.843791][  C118] sd 0:1:0:0: [sda] tag#230 UNKNOWN(0x2003) Result: =
hostbyte=3D0x01 driverbyte=3D0x00 cmd_age=3D1s=20
[ 9692.843866][   C64] Write-error on swap-device (254:1:63030016)=20
[ 9692.843891][   C96] sd 0:1:0:0: [sda] tag#877 CDB: opcode=3D0x2a 2a =
00 03 1e 48 00 00 02 00 00=20
[ 9692.844013][  C118] sd 0:1:0:0: [sda] tag#230 CDB: opcode=3D0x2a 2a =
00 03 c6 26 00 00 02 00 00=20
[ 9692.844615][   C92] Write-error on swap-device (254:1:39256640)=20
[ 9692.844643][   C64] Write-error on swap-device (254:1:63030024)=20
[ 9692.845109][   C61] Write-error on swap-device (254:1:17105384)=20
[ 9692.845192][   C25] page:fffff3b2ec3a8000 refcount:512 mapcount:0 =
mapping:000000009eb0338c index:0x7f6e58200 head:fffff3b2ec3a8000 order:9 =
compound_mapcount:0 compound_pincount:0=20
[ 9692.845226][   C25] anon flags: =
0x45fffe0000d8454(uptodate|lru|workingset|owner_priv_1|writeback|head|recl=
aim|swapbacked)=20
[ 9692.845254][   C25] raw: 045fffe0000d8454 fffff3b2f9d48008 =
fffff3b2f3270008 ffff97c3090f8209=20
[ 9692.845283][   C25] raw: 00000007f6e58200 000000000053c800 =
00000200ffffffff ffff97c8d71e9000=20
[ 9692.845293][  C122] Write-error on swap-device (254:1:39080184)=20
[ 9692.845316][  T213] page:fffff3b2f77d8000 refcount:512 mapcount:0 =
mapping:00000000a4517f4e index:0x7f69d2200 head:fffff3b2f77d8000 order:9 =
compound_mapcount:0 compound_pincount:0=20
[ 9692.845330][   C25] page dumped because: VM_BUG_ON_PAGE(1 && =
PageCompound(page))=20
[ 9692.845427][  T213] anon flags: =
0x45fffe0000d8454(uptodate|lru|workingset|owner_priv_1|writeback|head|recl=
aim|swapbacked)=20
[ 9692.845433][   C25] page->mem_cgroup:ffff97c8d71e9000=20
[ 9692.845443][   C25] page_owner tracks the page as allocated=20
[ 9692.845520][  T213] raw: 045fffe0000d8454 fffff3b2f5ec2f08 =
fffff3b2f6b88008 ffff97c715cc0609=20
[ 9692.845535][   C25] page last allocated via order 9, migratetype =
Movable, gfp_mask 0x1c20ca(GFP_TRANSHUGE_LIGHT)=20
[ 9692.845606][   C25]  prep_new_page+0x1cd/0x1f0=20
[ 9692.845628][   C25]  get_page_from_freelist+0x18ac/0x24d0=20
[ 9692.845639][  T213] raw: 00000007f69d2200 00000000000bf400 =
00000200ffffffff ffff97c8d71e9000=20
[ 9692.845654][   C25]  __alloc_pages_nodemask+0x1b1/0x450=20
[ 9692.845733][  T213] page dumped because: VM_BUG_ON_PAGE(1 && =
PageCompound(page))=20
[ 9692.845757][   C25]  alloc_pages_vma+0x8a/0x2c0=20
[ 9692.845762][  T213] page->mem_cgroup:ffff97c8d71e9000=20
[ 9692.845779][   C25]  do_huge_pmd_anonymous_page+0x1d4/0xc30=20
[ 9692.845786][  T213] page_owner tracks the page as allocated=20
[ 9692.845807][   C25]  __handle_mm_fault+0xd27/0xd50=20
[ 9692.845819][  T213] page last allocated via order 9, migratetype =
Movable, gfp_mask 0x1c20ca(GFP_TRANSHUGE_LIGHT)=20
[ 9692.845833][   C25]  handle_mm_fault+0xfc/0x2f0=20
[ 9692.845856][  T213]  prep_new_page+0x1cd/0x1f0=20
[ 9692.845876][   C25]  do_page_fault+0x263/0x6f9=20
[ 9692.845892][  T213]  get_page_from_free7219][   C25]  =
clone_endio+0xe4/0x2c0 [dm_mod]=20
[ 9692.847226][  T213] kernel BUG at include/linux/page-flags.h:317!=20
[ 9692.847234][   C64] Write-error on swap-device (254:1:63030064)=20
[ 9692.847250][   C25]  bio_endio+0x297/0x560=20
[ 9692.847255][   C61] Write-error on swap-device (254:1:17105424)=20
[ 9692.847263][   C25]  ? bio_advance+0x92/0x190=20
[ 9692.847267][  C122] Write-error on swap-device (254:1:39080224)=20
[ 9692.847276][   C25]  blk_update_request+0x201/0x920=20
[ 9692.847287][   C25]  ? ___ratelimit+0x138/0x1e0=20
[ 9692.847312][   C25]  scsi_end_request+0x6b/0x4b0=20
[ 9692.847320][   C25]  ? ___ratelimit+0x3e/0x1e0=20
[ 9692.847329][   C25]  scsi_io_completion+0x509/0x7e0=20
[ 9692.847340][   C25]  scsi_finish_command+0x1ed/0x2a0=20
[ 9692.847350][   C25]  scsi_softirq_done+0x1c9/0x1d0=20
[ 9692.847354][   C64] Write-error on swap-device (254:1:63030072)=20
[ 9692.847363][   C25]  ? blk_mq_check_inflight+0xa0/0xa0=20
[ 9692.847383][   C61] Write-error on swap-device (254:1:17105432)=20
[ 9692.847397][  C122] Write-erro692.848242][   C25] RSP: =
0018:ffffb02006b68bb0 EFLAGS: 00010086=20
[ 9692.848333][  T213] Workqueue: events pqi_ctrl_offline_worker =
[smartpqi]=20
[ 9692.848346][   C61] Write-error on swap-device (254:1:17105528)=20
[ 9692.848351][  C122] Write-error on swap-device (254:1:39080328)=20
[ 9692.848428][   C25] RAX: 0000000000000000 RBX: ffff97c76d8d4b80 RCX: =
ffffffff9d51e8f0=20
[ 9692.848433][   C61] Write-error on swap-device (254:1:17105536)=20
[ 9692.848437][  C122] Write-error on swap-device (254:1:39080336)=20
[ 9692.848445][  T213] RIP: 0010:end_swap_bio_write+0x90/0x280=20
[ 9692.848450][   C25] RDX: 0000000000000000 RSI: 0000000000000000 RDI: =
ffff97c7e539f00a=20
[ 9692.848461][  T213] Code: 80 7b 1a 00 0f 84 58 01 00 00 4c 89 e6 bf =
10 00 00 00 e8 33 f8 ff ff 84 c0 74 1d 48 c7 c6 18 7e 3b 9a 4c 89 e7 e8 =
20 78 fa ff <0f> 0b 48 c7 c7 b0 0b 6e 9a e8 04 ee 2b 00 4d 8d 74 24 08 =
ba 08 00=20
[ 9692.848466][   C25] RBP: ffffb02006b68bf0 R08: 0000000000000000 R09: =
000097c7e539f00a=20
[ 9692.848471][  T213] RSP: 0018:ffffb02006dd3908 EFLAGS: 00010286=20
[ 9692.848485][   C25] R10: 0000b02006b689a0 R11: 000097c7e5ax_pmem_core =
efivars acpi_cpufreq efivarfs ip_tables x_tables xfs sd_mod smartpqi =
scsi_transport_sas tg3 mlx5_core=20
[ 9692.849818][  C122] Write-error on swap-device (254:1:39080440)=20
[ 9692.849884][  T213]  libphy=20
[ 9692.849889][  C122] Write-error on swap-device (254:1:39080448)=20
[ 9692.849952][  T213]  firmware_class=20
[ 9692.849959][  C122] Write-error on swap-device (254:1:39080456)=20
[ 9692.849963][  T213]  dm_mirror dm_region_hash dm_log dm_mod=20
[ 9692.849990][  C122] Write-error on swap-device (254:1:39080464)=20
[ 9692.850069][  C122] Write-error on swap-device (254:1:39080472)=20
[ 9692.850107][  C122] Write-error on swap-device (254:1:39080480)=20
[ 9692.850156][  C122] Write-error on swap-device (254:1:39080488)=20
[ 9692.850220][  C122] Write-error on swap-device (254:1:39080496)=20
[ 9692.850264][  C122] Write-error on swap-device (254:1:39080504)=20
[ 9692.850323][  C122] Write-error on swap-device (254:1:39080512)=20
[ 9692.850361][  C122] Write-error on swap-device (254:1:39080520)=20
[ 9692.850411][  C122] Write-error on swap-device (254:1:39080528) =20

>=20
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> Cc: stable@vger.kernel.org
> Signed-off-by: Rafael Aquini <aquini@redhat.com>
> ---
> mm/mprotect.c | 38 ++++++++++++++++++++++++++++++++++++--
> 1 file changed, 36 insertions(+), 2 deletions(-)
>=20
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 7a8e84f86831..9ea8cc0ab2fd 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -161,6 +161,31 @@ static unsigned long change_pte_range(struct =
vm_area_struct *vma, pmd_t *pmd,
> 	return pages;
> }
>=20
> +/*
> + * Used when setting automatic NUMA hinting protection where it is
> + * critical that a numa hinting PMD is not confused with a bad PMD.
> + */
> +static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
> +{
> +	pmd_t pmdval =3D pmd_read_atomic(pmd);
> +
> +	/* See pmd_none_or_trans_huge_or_clear_bad for info on barrier =
*/
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +	barrier();
> +#endif
> +
> +	if (pmd_none(pmdval))
> +		return 1;
> +	if (pmd_trans_huge(pmdval))
> +		return 0;
> +	if (unlikely(pmd_bad(pmdval))) {
> +		pmd_clear_bad(pmd);
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
> static inline unsigned long change_pmd_range(struct vm_area_struct =
*vma,
> 		pud_t *pud, unsigned long addr, unsigned long end,
> 		pgprot_t newprot, int dirty_accountable, int prot_numa)
> @@ -178,8 +203,17 @@ static inline unsigned long =
change_pmd_range(struct vm_area_struct *vma,
> 		unsigned long this_pages;
>=20
> 		next =3D pmd_addr_end(addr, end);
> -		if (!is_swap_pmd(*pmd) && !pmd_trans_huge(*pmd) && =
!pmd_devmap(*pmd)
> -				&& pmd_none_or_clear_bad(pmd))
> +
> +		/*
> +		 * Automatic NUMA balancing walks the tables with =
mmap_sem
> +		 * held for read. It's possible a parallel update to =
occur
> +		 * between pmd_trans_huge() and a =
pmd_none_or_clear_bad()
> +		 * check leading to a false positive and clearing.
> +		 * Hence, it's ecessary to atomically read the PMD value
> +		 * for all the checks.
> +		 */
> +		if (!is_swap_pmd(*pmd) && !pmd_devmap(*pmd) &&
> +		     pmd_none_or_clear_bad_unless_trans_huge(pmd))
> 			goto next;
>=20
> 		/* invoke the mmu notifier if the pmd is populated */
> --=20
> 2.24.1
>=20
>=20