On Wed 28-06-17 13:12:49, Kirill A. Shutemov wrote:
> Reinette reported following crash:
>
> BUG: Bad page state in process log2exe pfn:57600
> page:ffffea00015d8000 count:0 mapcount:0 mapping: (null) index:0x20200
> flags: 0x4000000000040019(locked|uptodate|dirty|swapbacked)
> raw: 4000000000040019 0000000000000000 0000000000020200 00000000ffffffff
> raw: ffffea00015d8020 ffffea00015d8020 0000000000000000 0000000000000000
> page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
> bad because of flags: 0x1(locked)
> Modules linked in: rfcomm 8021q bnep intel_rapl x86_pkg_temp_thermal coretemp efivars btusb btrtl btbcm pwm_lpss_pci snd_hda_codec_hdmi btintel pwm_lpss snd_hda_codec_realtek snd_soc_skl snd_hda_codec_generic snd_soc_skl_ipc spi_pxa2xx_platform snd_soc_sst_ipc snd_soc_sst_dsp i2c_designware_platform i2c_designware_core snd_hda_ext_core snd_soc_sst_match snd_hda_intel snd_hda_codec mei_me snd_hda_core mei snd_soc_rt286 snd_soc_rl6347a snd_soc_core efivarfs
> CPU: 1 PID: 354 Comm: log2exe Not tainted 4.12.0-rc7-test-test #19
> Hardware name: Intel corporation NUC6CAYS/NUC6CAYB, BIOS AYAPLCEL.86A.0027.2016.1108.1529 11/08/2016
> Call Trace:
> dump_stack+0x95/0xeb
> bad_page+0x16a/0x1f0
> free_pages_check_bad+0x117/0x190
> ? rcu_read_lock_sched_held+0xa8/0x130
> free_hot_cold_page+0x7b1/0xad0
> __put_page+0x70/0xa0
> madvise_free_huge_pmd+0x627/0x7b0
> madvise_free_pte_range+0x6f8/0x1150
> ? debug_check_no_locks_freed+0x280/0x280
> ? swapin_walk_pmd_entry+0x380/0x380
> __walk_page_range+0x6b5/0xe30
> walk_page_range+0x13b/0x310
> madvise_free_page_range.isra.16+0xad/0xd0
> ? force_swapin_readahead+0x110/0x110
> ? swapin_walk_pmd_entry+0x380/0x380
> ? lru_add_drain_cpu+0x160/0x320
> madvise_free_single_vma+0x2e4/0x470
> ? madvise_free_page_range.isra.16+0xd0/0xd0
> ? vmacache_update+0x100/0x130
> ? find_vma+0x35/0x160
> SyS_madvise+0x8ce/0x1450
>
> If somebody frees the page under us and we hold the last reference to
> it, put_page() would attempt to free the page before unlocking it.
>
> The fix is trivial reorder of operations.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Reported-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> Fixes: 9818b8cde622 ("madvise_free, thp: fix madvise_free_huge_pmd return value after splitting")
> Cc: Huang Ying <ying.huang@xxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/huge_memory.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 8624450f7106..25b5965c1130 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -1575,8 +1575,8 @@ bool madvise_free_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
> get_page(page);
> spin_unlock(ptl);
> split_huge_page(page);
> - put_page(page);
> unlock_page(page);
> + put_page(page);
> goto out_unlocked;
> }
I was about to ask what prevents get_page on an already freed page but
then I've noticed that this is still under pmd_trans_huge_lock which is
released right after that said get_page.
--
Michal Hocko
SUSE Labs
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