Re: [PATCH v15] mm, pmem, xfs: Introduce MF_MEM_PRE_REMOVE for unbind

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On Mon, Oct 23, 2023 at 03:26:52 PM +0800, Shiyang Ruan wrote:
> 在 2023/10/23 14:40, Chandan Babu R 写道:
>> On Fri, Oct 20, 2023 at 08:40:09 AM -0700, Darrick J. Wong wrote:
>>> On Fri, Oct 20, 2023 at 03:26:32PM +0530, Chandan Babu R wrote:
>>>> On Thu, Sep 28, 2023 at 06:32:27 PM +0800, Shiyang Ruan wrote:
>>>>> ====
>>>>> Changes since v14:
>>>>>   1. added/fixed code comments per Dan's comments
>>>>> ====
>>>>>
>>>>> Now, if we suddenly remove a PMEM device(by calling unbind) which
>>>>> contains FSDAX while programs are still accessing data in this device,
>>>>> e.g.:
>>>>> ```
>>>>>   $FSSTRESS_PROG -d $SCRATCH_MNT -n 99999 -p 4 &
>>>>>   # $FSX_PROG -N 1000000 -o 8192 -l 500000 $SCRATCH_MNT/t001 &
>>>>>   echo "pfn1.1" > /sys/bus/nd/drivers/nd_pmem/unbind
>>>>> ```
>>>>> it could come into an unacceptable state:
>>>>>    1. device has gone but mount point still exists, and umount will fail
>>>>>         with "target is busy"
>>>>>    2. programs will hang and cannot be killed
>>>>>    3. may crash with NULL pointer dereference
>>>>>
>>>>> To fix this, we introduce a MF_MEM_PRE_REMOVE flag to let it know that we
>>>>> are going to remove the whole device, and make sure all related processes
>>>>> could be notified so that they could end up gracefully.
>>>>>
>>>>> This patch is inspired by Dan's "mm, dax, pmem: Introduce
>>>>> dev_pagemap_failure()"[1].  With the help of dax_holder and
>>>>> ->notify_failure() mechanism, the pmem driver is able to ask filesystem
>>>>> on it to unmap all files in use, and notify processes who are using
>>>>> those files.
>>>>>
>>>>> Call trace:
>>>>> trigger unbind
>>>>>   -> unbind_store()
>>>>>    -> ... (skip)
>>>>>     -> devres_release_all()
>>>>>      -> kill_dax()
>>>>>       -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_PRE_REMOVE)
>>>>>        -> xfs_dax_notify_failure()
>>>>>        `-> freeze_super()             // freeze (kernel call)
>>>>>        `-> do xfs rmap
>>>>>        ` -> mf_dax_kill_procs()
>>>>>        `  -> collect_procs_fsdax()    // all associated processes
>>>>>        `  -> unmap_and_kill()
>>>>>        ` -> invalidate_inode_pages2_range() // drop file's cache
>>>>>        `-> thaw_super()               // thaw (both kernel & user call)
>>>>>
>>>>> Introduce MF_MEM_PRE_REMOVE to let filesystem know this is a remove
>>>>> event.  Use the exclusive freeze/thaw[2] to lock the filesystem to prevent
>>>>> new dax mapping from being created.  Do not shutdown filesystem directly
>>>>> if configuration is not supported, or if failure range includes metadata
>>>>> area.  Make sure all files and processes(not only the current progress)
>>>>> are handled correctly.  Also drop the cache of associated files before
>>>>> pmem is removed.
>>>>>
>>>>> [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>>>>> [2]: https://lore.kernel.org/linux-xfs/169116275623.3187159.16862410128731457358.stg-ugh@frogsfrogsfrogs/
>>>>>
>>>>> Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
>>>>> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
>>>>> Acked-by: Dan Williams <dan.j.williams@xxxxxxxxx>
>>>>
>>>> Hi Andrew,
>>>>
>>>> Shiyang had indicated that this patch has been added to
>>>> akpm/mm-hotfixes-unstable branch. However, I don't see the patch listed in
>>>> that branch.
>>>>
>>>> I am about to start collecting XFS patches for v6.7 cycle. Please let me know
>>>> if you have any objections with me taking this patch via the XFS tree.
>>>
>>> V15 was dropped from his tree on 28 Sept., you might as well pull it
>>> into your own tree for 6.7.  It's been testing fine on my trees for the
>>> past 3 weeks.
>>>
>>> https://lore.kernel.org/mm-commits/20230928172815.EE6AFC433C8@xxxxxxxxxxxxxxx/
>> Shiyang, this patch does not apply cleanly on v6.6-rc7. Can you
>> please rebase
>> the patch on v6.6-rc7 and send it to the mailing list?
>
> Sure.  I have rebased it and sent a v15.1.  Please check it:
>
> https://lore.kernel.org/linux-xfs/20231023072046.1626474-1-ruansy.fnst@xxxxxxxxxxx/

Thank you. I have applied the patch to my local Git tree.

-- 
Chandan





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