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Message-ID: <72fa9657-741a-e099-baf8-4615145d7bd1@fujitsu.com>
Date:   Mon, 29 Aug 2022 18:02:11 +0800
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Subject: Re: [PATCH v7] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind
To:     Dan Williams <dan.j.williams@intel.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
        "nvdimm@lists.linux.dev" <nvdimm@lists.linux.dev>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>
CC:     "djwong@kernel.org" <djwong@kernel.org>,
        "david@fromorbit.com" <david@fromorbit.com>,
        "hch@infradead.org" <hch@infradead.org>,
        "jane.chu@oracle.com" <jane.chu@oracle.com>
References: <9e9521a4-6e07-e226-2814-b78a2451656b@fujitsu.com>
 <63093cbd43f67_259e5b2946d@dwillia2-xfh.jf.intel.com.notmuch>
From:   Shiyang Ruan <ruansy.fnst@fujitsu.com>
In-Reply-To: <63093cbd43f67_259e5b2946d@dwillia2-xfh.jf.intel.com.notmuch>
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在 2022/8/27 5:35, Dan Williams 写道:
> Shiyang Ruan wrote:
>> 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
>> (or mapped device) 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()
>>
>> Introduce MF_MEM_PRE_REMOVE to let filesystem know this is a remove
>> event.  So do not shutdown filesystem directly if something not
>> supported, or if failure range includes metadata area.  Make sure all
>> files and processes are handled correctly.
>>
>> ==
>> Changes since v6:
>>     1. Rebase on 6.0-rc2 and Darrick's patch[2].
>>
>> Changes since v5:
>>     1. Renamed MF_MEM_REMOVE to MF_MEM_PRE_REMOVE
>>     2. hold s_umount before sync_filesystem()
>>     3. do sync_filesystem() after SB_BORN check
>>     4. Rebased on next-20220714
>>
>> [1]:
>> https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@dwillia2-desk3.amr.corp.intel.com/
>> [2]: https://lore.kernel.org/linux-xfs/Yv5wIa2crHioYeRr@magnolia/
>>
>> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
>> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
>> ---
>>    drivers/dax/super.c         |  3 ++-
>>    fs/xfs/xfs_notify_failure.c | 15 +++++++++++++++
>>    include/linux/mm.h          |  1 +
>>    3 files changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
>> index 9b5e2a5eb0ae..cf9a64563fbe 100644
>> --- a/drivers/dax/super.c
>> +++ b/drivers/dax/super.c
>> @@ -323,7 +323,8 @@ void kill_dax(struct dax_device *dax_dev)
>>    		return;
>>     	if (dax_dev->holder_data != NULL)
>> -		dax_holder_notify_failure(dax_dev, 0, U64_MAX, 0);
>> +		dax_holder_notify_failure(dax_dev, 0, U64_MAX,
>> +				MF_MEM_PRE_REMOVE);
>>     	clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
>>    	synchronize_srcu(&dax_srcu);
>> diff --git a/fs/xfs/xfs_notify_failure.c b/fs/xfs/xfs_notify_failure.c
>> index 65d5eb20878e..a9769f17e998 100644
>> --- a/fs/xfs/xfs_notify_failure.c
>> +++ b/fs/xfs/xfs_notify_failure.c
>> @@ -77,6 +77,9 @@ xfs_dax_failure_fn(
>>     	if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
>>    	    (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) {
>> +		/* Do not shutdown so early when device is to be removed */
>> +		if (notify->mf_flags & MF_MEM_PRE_REMOVE)
>> +			return 0;
>>    		notify->want_shutdown = true;
>>    		return 0;
>>    	}
>> @@ -182,12 +185,22 @@ xfs_dax_notify_failure(
>>    	struct xfs_mount	*mp = dax_holder(dax_dev);
>>    	u64			ddev_start;
>>    	u64			ddev_end;
>> +	int			error;
>>     	if (!(mp->m_sb.sb_flags & SB_BORN)) {
> 
> How are you testing the SB_BORN interactions? I have a fix for this
> pending here:
> 
> https://lore.kernel.org/nvdimm/166153428094.2758201.7936572520826540019.stgit@dwillia2-xfh.jf.intel.com/

That was my mistake.  Yes, it should be mp->m_super->s_flags.

(I remember my testcase did pass in my dev version, but now that seems 
impossible.  I think something was wrong when I did the test.)

> 
>>    		xfs_warn(mp, "filesystem is not ready for notify_failure()!");
>>    		return -EIO;
>>    	}
>>    +	if (mf_flags & MF_MEM_PRE_REMOVE) {
> 
> It appears this patch is corrupted here. I confirmed that b4 sees the
> same when trying to apply it.

Can't this patch be applied?  It is based on 6.0-rc2 + Darrick's patch. 
It's also ok to rebase on 6.0-rc3 + Darrick's patch.

> 
>> +		xfs_info(mp, "device is about to be removed!");
>> +		down_write(&mp->m_super->s_umount);
>> +		error = sync_filesystem(mp->m_super);
> 
> This syncs to make data persistent, but for DAX this also needs to get
> invalidate all current DAX mappings. I do not see that in these changes.

I'll add it.


--
Thanks,
Ruan.

> 
>> +		up_write(&mp->m_super->s_umount);
>> +		if (error)
>> +			return error;
>> +	}
>> +
>>    	if (mp->m_rtdev_targp && mp->m_rtdev_targp->bt_daxdev == dax_dev) {
>>    		xfs_warn(mp,
>>    			 "notify_failure() not supported on realtime device!");
>> @@ -196,6 +209,8 @@ xfs_dax_notify_failure(
>>     	if (mp->m_logdev_targp && mp->m_logdev_targp->bt_daxdev == dax_dev &&
>>    	    mp->m_logdev_targp != mp->m_ddev_targp) {
>> +		if (mf_flags & MF_MEM_PRE_REMOVE)
>> +			return 0;
>>    		xfs_err(mp, "ondisk log corrupt, shutting down fs!");
>>    		xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
>>    		return -EFSCORRUPTED;
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 982f2607180b..2c7c132e6512 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -3176,6 +3176,7 @@ enum mf_flags {
>>    	MF_UNPOISON = 1 << 4,
>>    	MF_SW_SIMULATED = 1 << 5,
>>    	MF_NO_RETRY = 1 << 6,
>> +	MF_MEM_PRE_REMOVE = 1 << 7,
>>    };
>>    int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
>>    		      unsigned long count, int mf_flags);
>> -- 
>> 2.37.2
>>
>>
> 
>