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Date:   Fri, 26 Aug 2022 14:35:57 -0700
From:   Dan Williams <dan.j.williams@intel.com>
To:     Shiyang Ruan <ruansy.fnst@fujitsu.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
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CC:     "djwong@kernel.org" <djwong@kernel.org>,
        "dan.j.williams@intel.com" <dan.j.williams@intel.com>,
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        "hch@infradead.org" <hch@infradead.org>,
        "jane.chu@oracle.com" <jane.chu@oracle.com>
Subject: RE: [PATCH v7] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind
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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/

>   		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.

> +		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.

> +		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
> 
>