Re: [PATCH] mm, numa: fix bad pmd by atomically check for pmd_trans_huge when marking page tables prot_numa

From: Rafael Aquini
Date: Mon Mar 09 2020 - 11:05:48 EST

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On Sun, Mar 08, 2020 at 11:27:22PM -0400, Qian Cai wrote:
>
>
> > On Mar 8, 2020, at 7:14 PM, Rafael Aquini <aquini@xxxxxxxxxx> wrote:
> >
> > On Sat, Mar 07, 2020 at 10:20:20PM -0500, Qian Cai wrote:
> >> Not sure if it is really worth hurrying this into -rc5 now given...
> >>
> >>> On Mar 6, 2020, at 10:05 PM, Rafael Aquini <aquini@xxxxxxxxxx> wrote:
> >>>>
> >>>> After reverted this patch, it is no longer possible to reproduce a bug under memory pressure
> >>>> with swapping on linux-next 20200306,
> >>>>
> >>>
> >>> Would you mind sharing your .config ? Also it would be nice to know your
> >>> system and workload details so I can try to reproduce.
> >>
> >> LTP oom02 in a tight loop,
> >>
> >> # i=0; while :; echo $((i++)); ./oom02; sleep 10; done
> >>
> >> HPE ProLiant DL385 Gen10
> >> AMD EPYC 7601 32-Core Processor
> >> 65536 MB memory, 400 GB disk space
> >>
> >> Processors 128
> >> Cores 64
> >> Sockets 2
> >>
> >> linux-next 20200306
> >>
> >
> > Thx! what about your .config?
>
> https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config
>
> My theory is this race,
>
> From 73d4e8dad6cb248970bade5049cc072cd9090d0f Mon Sep 17 00:00:00 2001
> From: Qian Cai <cai@xxxxxx>
> Date: Sun, 8 Mar 2020 17:37:51 -0400
> Subject: [PATCH] mm/mprotect: fix a race in change_pmd_range()
>
> The recent commit increased the race window between,
>
> CPU0:
> task_numa_work()
> change_prot_numa()
> change_protection()
> change_protection_range()
> change_pmd_range()
> pmd_none_or_clear_bad_unless_trans_huge(pmd) <-- PMD is NULL.
> goto next;
> CPU1:
> do_huge_pmd_anonymous_page()
> __do_huge_pmd_anonymous_page()
> PMD is transhuge.
>
> where it will not calling __split_huge_pmd() properly and trigger a
> crash later on,
>
> kernel BUG at include/linux/page-flags.h:317!
>
> end_swap_bio_write()
> SetPageError(page)
> VM_BUG_ON_PAGE(1 && PageCompound(page))
>
> Fix it by using a similar check in pmd_trans_unstable().
>
> Fixes: 8b272b3cbbb5 ("mm, numa: fix bad pmd by atomically check for pmd_trans_huge when marking page tables prot_numa")
> Signed-off-by: Qian Cai <cai@xxxxxx>
> ---
> mm/mprotect.c | 8 +++-----
> 1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/mm/mprotect.c b/mm/mprotect.c
> index 311c0dadf71c..00dd2c66a434 100644
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -165,7 +165,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
> * 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)
> +static inline int pmd_clear_bad_unless_none_or_trans_huge(pmd_t *pmd)
> {
> pmd_t pmdval = pmd_read_atomic(pmd);
>
> @@ -174,9 +174,7 @@ static inline int pmd_none_or_clear_bad_unless_trans_huge(pmd_t *pmd)
> barrier();
> #endif
>
> - if (pmd_none(pmdval))
> - return 1;
> - if (pmd_trans_huge(pmdval))
> + if (pmd_none(pmdval) || pmd_trans_huge(pmdval))

I'm still waiting on a similar system to become available, so I can
work on your reproducer case, as well as to dig and wrap my head around it.

I still don't think that skipping the pmd_none() in the change-protection walk
should cause a big fuss like you observed here (yet, it seems it does), and
the fact that we need that race window to take the __split_huge_pmd() suggests,
at least to me, that we might be missing this proper split somewhere else.

> if (unlikely(pmd_bad(pmdval))) {
> pmd_clear_bad(pmd);
> @@ -213,7 +211,7 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
> * for all the checks.
> */
> if (!is_swap_pmd(*pmd) && !pmd_devmap(*pmd) &&
> - pmd_none_or_clear_bad_unless_trans_huge(pmd))
> + pmd_clear_bad_unless_none_or_trans_huge(pmd))
> goto next;
>
> /* invoke the mmu notifier if the pmd is populated */
> --
> 2.21.0 (Apple Git-122.2)
>
>
> >
> >
> >
> > Cheers,
> > -- Rafael
> >
> >>>> 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))
> >>>>
> >>>> 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
> >>>> [ 9690.896638][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc0000 flags=0x0010]
> >>>> [ 9690.910129][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc1000 flags=0x0010]
> >>>> [ 9690.923933][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc1900 flags=0x0010]
> >>>> [ 9690.937669][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc1d00 flags=0x0010]
> >>>> [ 9690.951468][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc2000 flags=0x0010]
> >>>> [ 9690.964803][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc2400 flags=0x0010]
> >>>> [ 9690.978256][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc2800 flags=0x0010]
> >>>> [ 9690.991423][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc2c00 flags=0x0010]
> >>>> [ 9691.004294][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc3000 flags=0x0010]
> >>>> [ 9691.017228][ T814] smartpqi 0000:23:00.0: AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0027 address=0xffffffffffcc3400 flags=0x0010]
> >>>> [ 9691.029804][ T814] AMD-Vi: Event logged [IO_PAGE_FAULT device=23:00.0 domain=0x0027 address=0xffffffffffcc3800 flags=0x0010]
> >>>> [ 9691.041623][ T814] AMD-Vi: Event logged [IO_PAGE_FAULT device=23:00.0 domain=0x0027 address=0xffffffffffcc3c00 flags=0x0010]
> >>>> [ 9692.767064][ C8] smartpqi 0000:23:00.0: controller is offline: status code 0x14803
> >>>> [ 9692.775562][ C8] smartpqi 0000:23:00.0: controller offline
> >>>> [ 9692.841721][ C36] sd 0:1:0:0: [sda] tag#693 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.841970][ C87] blk_update_request: I/O error, dev sda, sector 59046400 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.842718][ C31] blk_update_request: I/O error, dev sda, sector 36509696 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.842748][ C18] sd 0:1:0:0: [sda] tag#616 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.842757][ C28] sd 0:1:0:0: [sda] tag#841 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.842766][ C109] sd 0:1:0:0: [sda] tag#393 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.842811][ C109] sd 0:1:0:0: [sda] tag#393 CDB: opcode=0x2a 2a 00 01 60 c8 00 00 02 00 00
> >>>> [ 9692.842840][ C13] sd 0:1:0:0: [sda] tag#324 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.842924][ C18] sd 0:1:0:0: [sda] tag#616 CDB: opcode=0x2a 2a 00 01 c7 8c 00 00 02 00 00
> >>>> [ 9692.842932][ C109] blk_update_request: I/O error, dev sda, sector 23119872 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.842938][ C28] sd 0:1:0:0: [sda] tag#841 CDB: opcode=0x2a 2a 00 03 2f cc 00 00 02 00 00
> >>>> [ 9692.842984][ T213] sd 0:1:0:0: [sda] tag#47 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.842995][ C28] blk_update_request: I/O error, dev sda, sector 53464064 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.843000][ C81] sd 0:1:0:0: [sda] tag#10 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.843031][ C18] blk_update_request: I/O error, dev sda, sector 29854720 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.843056][ C13] sd 0:1:0:0: [sda] tag#324 CDB: opcode=0x2a 2a 00 03 17 66 00 00 02 00 00
> >>>> [ 9692.843101][ C81] sd 0:1:0:0: [sda] tag#10 CDB: opcode=0x2a 2a 00 00 52 a4 00 00 02 00 00
> >>>> [ 9692.843129][ C13] blk_update_request: I/O error, dev sda, sector 51865088 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.843192][ C81] blk_update_request: I/O error, dev sda, sector 5415936 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.843338][ T213] sd 0:1:0:0: [sda] tag#47 CDB: opcode=0x2a 2a 00 02 be 5a 00 00 02 00 00
> >>>> [ 9692.843358][ C13] sd 0:1:0:0: [sda] tag#325 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.843480][ T213] blk_update_request: I/O error, dev sda, sector 46029312 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.843485][ C13] sd 0:1:0:0: [sda] tag#325 CDB: opcode=0x2a 2a 00 03 17 68 00 00 02 00 00
> >>>> [ 9692.843510][ C13] blk_update_request: I/O error, dev sda, sector 51865600 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.843685][ C103] blk_update_request: I/O error, dev sda, sector 34941952 op 0x1:(WRITE) flags 0x8004000 phys_seg 4 prio class 0
> >>>> [ 9692.843725][ C96] sd 0:1:0:0: [sda] tag#877 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.843744][ C92] Write-error on swap-device (254:1:39256632)
> >>>> [ 9692.843791][ C118] sd 0:1:0:0: [sda] tag#230 UNKNOWN(0x2003) Result: hostbyte=0x01 driverbyte=0x00 cmd_age=1s
> >>>> [ 9692.843866][ C64] Write-error on swap-device (254:1:63030016)
> >>>> [ 9692.843891][ C96] sd 0:1:0:0: [sda] tag#877 CDB: opcode=0x2a 2a 00 03 1e 48 00 00 02 00 00
> >>>> [ 9692.844013][ C118] sd 0:1:0:0: [sda] tag#230 CDB: opcode=0x2a 2a 00 03 c6 26 00 00 02 00 00
> >>>> [ 9692.844615][ C92] Write-error on swap-device (254:1:39256640)
> >>>> [ 9692.844643][ C64] Write-error on swap-device (254:1:63030024)
> >>>> [ 9692.845109][ C61] Write-error on swap-device (254:1:17105384)
> >>>> [ 9692.845192][ C25] page:fffff3b2ec3a8000 refcount:512 mapcount:0 mapping:000000009eb0338c index:0x7f6e58200 head:fffff3b2ec3a8000 order:9 compound_mapcount:0 compound_pincount:0
> >>>> [ 9692.845226][ C25] anon flags: 0x45fffe0000d8454(uptodate|lru|workingset|owner_priv_1|writeback|head|reclaim|swapbacked)
> >>>> [ 9692.845254][ C25] raw: 045fffe0000d8454 fffff3b2f9d48008 fffff3b2f3270008 ffff97c3090f8209
> >>>> [ 9692.845283][ C25] raw: 00000007f6e58200 000000000053c800 00000200ffffffff ffff97c8d71e9000
> >>>> [ 9692.845293][ C122] Write-error on swap-device (254:1:39080184)
> >>>> [ 9692.845316][ T213] page:fffff3b2f77d8000 refcount:512 mapcount:0 mapping:00000000a4517f4e index:0x7f69d2200 head:fffff3b2f77d8000 order:9 compound_mapcount:0 compound_pincount:0
> >>>> [ 9692.845330][ C25] page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
> >>>> [ 9692.845427][ T213] anon flags: 0x45fffe0000d8454(uptodate|lru|workingset|owner_priv_1|writeback|head|reclaim|swapbacked)
> >>>> [ 9692.845433][ C25] page->mem_cgroup:ffff97c8d71e9000
> >>>> [ 9692.845443][ C25] page_owner tracks the page as allocated
> >>>> [ 9692.845520][ T213] raw: 045fffe0000d8454 fffff3b2f5ec2f08 fffff3b2f6b88008 ffff97c715cc0609
> >>>> [ 9692.845535][ C25] page last allocated via order 9, migratetype Movable, gfp_mask 0x1c20ca(GFP_TRANSHUGE_LIGHT)
> >>>> [ 9692.845606][ C25] prep_new_page+0x1cd/0x1f0
> >>>> [ 9692.845628][ C25] get_page_from_freelist+0x18ac/0x24d0
> >>>> [ 9692.845639][ T213] raw: 00000007f69d2200 00000000000bf400 00000200ffffffff ffff97c8d71e9000
> >>>> [ 9692.845654][ C25] __alloc_pages_nodemask+0x1b1/0x450
> >>>> [ 9692.845733][ T213] page dumped because: VM_BUG_ON_PAGE(1 && PageCompound(page))
> >>>> [ 9692.845757][ C25] alloc_pages_vma+0x8a/0x2c0
> >>>> [ 9692.845762][ T213] page->mem_cgroup:ffff97c8d71e9000
> >>>> [ 9692.845779][ C25] do_huge_pmd_anonymous_page+0x1d4/0xc30
> >>>> [ 9692.845786][ T213] page_owner tracks the page as allocated
> >>>> [ 9692.845807][ C25] __handle_mm_fault+0xd27/0xd50
> >>>> [ 9692.845819][ T213] page last allocated via order 9, migratetype Movable, gfp_mask 0x1c20ca(GFP_TRANSHUGE_LIGHT)
> >>>> [ 9692.845833][ C25] handle_mm_fault+0xfc/0x2f0
> >>>> [ 9692.845856][ T213] prep_new_page+0x1cd/0x1f0
> >>>> [ 9692.845876][ C25] do_page_fault+0x263/0x6f9
> >>>> [ 9692.845892][ T213] get_page_from_free7219][ C25] clone_endio+0xe4/0x2c0 [dm_mod]
> >>>> [ 9692.847226][ T213] kernel BUG at include/linux/page-flags.h:317!
> >>>> [ 9692.847234][ C64] Write-error on swap-device (254:1:63030064)
> >>>> [ 9692.847250][ C25] bio_endio+0x297/0x560
> >>>> [ 9692.847255][ C61] Write-error on swap-device (254:1:17105424)
> >>>> [ 9692.847263][ C25] ? bio_advance+0x92/0x190
> >>>> [ 9692.847267][ C122] Write-error on swap-device (254:1:39080224)
> >>>> [ 9692.847276][ C25] blk_update_request+0x201/0x920
> >>>> [ 9692.847287][ C25] ? ___ratelimit+0x138/0x1e0
> >>>> [ 9692.847312][ C25] scsi_end_request+0x6b/0x4b0
> >>>> [ 9692.847320][ C25] ? ___ratelimit+0x3e/0x1e0
> >>>> [ 9692.847329][ C25] scsi_io_completion+0x509/0x7e0
> >>>> [ 9692.847340][ C25] scsi_finish_command+0x1ed/0x2a0
> >>>> [ 9692.847350][ C25] scsi_softirq_done+0x1c9/0x1d0
> >>>> [ 9692.847354][ C64] Write-error on swap-device (254:1:63030072)
> >>>> [ 9692.847363][ C25] ? blk_mq_check_inflight+0xa0/0xa0
> >>>> [ 9692.847383][ C61] Write-error on swap-device (254:1:17105432)
> >>>> [ 9692.847397][ C122] Write-erro692.848242][ C25] RSP: 0018:ffffb02006b68bb0 EFLAGS: 00010086
> >>>> [ 9692.848333][ T213] Workqueue: events pqi_ctrl_offline_worker [smartpqi]
> >>>> [ 9692.848346][ C61] Write-error on swap-device (254:1:17105528)
> >>>> [ 9692.848351][ C122] Write-error on swap-device (254:1:39080328)
> >>>> [ 9692.848428][ C25] RAX: 0000000000000000 RBX: ffff97c76d8d4b80 RCX: ffffffff9d51e8f0
> >>>> [ 9692.848433][ C61] Write-error on swap-device (254:1:17105536)
> >>>> [ 9692.848437][ C122] Write-error on swap-device (254:1:39080336)
> >>>> [ 9692.848445][ T213] RIP: 0010:end_swap_bio_write+0x90/0x280
> >>>> [ 9692.848450][ C25] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff97c7e539f00a
> >>>> [ 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
> >>>> [ 9692.848466][ C25] RBP: ffffb02006b68bf0 R08: 0000000000000000 R09: 000097c7e539f00a
> >>>> [ 9692.848471][ T213] RSP: 0018:ffffb02006dd3908 EFLAGS: 00010286
> >>>> [ 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
> >>>> [ 9692.849818][ C122] Write-error on swap-device (254:1:39080440)
> >>>> [ 9692.849884][ T213] libphy
> >>>> [ 9692.849889][ C122] Write-error on swap-device (254:1:39080448)
> >>>> [ 9692.849952][ T213] firmware_class
> >>>> [ 9692.849959][ C122] Write-error on swap-device (254:1:39080456)
> >>>> [ 9692.849963][ T213] dm_mirror dm_region_hash dm_log dm_mod
> >>>> [ 9692.849990][ C122] Write-error on swap-device (254:1:39080464)
> >>>> [ 9692.850069][ C122] Write-error on swap-device (254:1:39080472)
> >>>> [ 9692.850107][ C122] Write-error on swap-device (254:1:39080480)
> >>>> [ 9692.850156][ C122] Write-error on swap-device (254:1:39080488)
> >>>> [ 9692.850220][ C122] Write-error on swap-device (254:1:39080496)
> >>>> [ 9692.850264][ C122] Write-error on swap-device (254:1:39080504)
> >>>> [ 9692.850323][ C122] Write-error on swap-device (254:1:39080512)
> >>>> [ 9692.850361][ C122] Write-error on swap-device (254:1:39080520)
> >>>> [ 9692.850411][ C122] Write-error on swap-device (254:1:39080528)
> >>>>
> >>>>>
> >>>>> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> >>>>> Cc: stable@xxxxxxxxxxxxxxx
> >>>>> Signed-off-by: Rafael Aquini <aquini@xxxxxxxxxx>
> >>>>> ---
> >>>>> mm/mprotect.c | 38 ++++++++++++++++++++++++++++++++++++--
> >>>>> 1 file changed, 36 insertions(+), 2 deletions(-)
> >>>>>
> >>>>> 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;
> >>>>> }
> >>>>>
> >>>>> +/*
> >>>>> + * 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 = 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;
> >>>>>
> >>>>> next = 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;
> >>>>>
> >>>>> /* invoke the mmu notifier if the pmd is populated */
> >>>>> --
> >>>>> 2.24.1
>

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