Re: + thp-mm-fix-crash-due-race-in-madv_free-handling.patch added to -mm tree

[Minchan Kim <minchan@kernel.org>]

Hi Andrew,

On Thu, Jun 29, 2017 at 01:53:08PM -0700, akpm@linux-foundation.org wrote:
> 
> The patch titled
>      Subject: thp, mm: fix crash due race in MADV_FREE handling
> has been added to the -mm tree.  Its filename is
>      thp-mm-fix-crash-due-race-in-madv_free-handling.patch
> 
> This patch should soon appear at
>     http://ozlabs.org/~akpm/mmots/broken-out/thp-mm-fix-crash-due-race-in-madv_free-handling.patch
> and later at
>     http://ozlabs.org/~akpm/mmotm/broken-out/thp-mm-fix-crash-due-race-in-madv_free-handling.patch
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
> 
> The -mm tree is included into linux-next and is updated
> there every 3-4 working days
> 
> ------------------------------------------------------
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Subject: thp, mm: fix crash due race in MADV_FREE handling
> 
> 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.
> 
> Dave said:
> 
> : I came up with the exact same patch.  For posterity, here's the test
> : case, generated by syzkaller and trimmed down by Reinette:
> : 
> : 	https://www.sr71.net/~dave/intel/log2.c
> : 
> : And the config that helps detect this:
> : 
> : 	https://www.sr71.net/~dave/intel/config-log2
> 
> Fixes: 9818b8cde622 ("madvise_free, thp: fix madvise_free_huge_pmd return value after splitting")

Bad commit to be fixed is not 9818b8cde622 but b8d3c4c3009d as Kirill sent
again https://marc.info/?l=linux-mm&m=149872564723003&w=2.

Thanks.