linux-kernel - Re: [RFC PATCH v6] mm, pmem, xfs: Introduce MF_MEM

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Date:   Thu, 14 Jul 2022 10:54:14 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>,
        "nvdimm@...ts.linux.dev" <nvdimm@...ts.linux.dev>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "david@...morbit.com" <david@...morbit.com>,
        "hch@...radead.org" <hch@...radead.org>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>
Subject: Re: [RFC PATCH v6] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

On Thu, Jul 14, 2022 at 10:34:29AM +0000, ruansy.fnst@...itsu.com 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()   # was pmem driver ->remove() in v1
>     -> 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 v5:
>   1. Renamed MF_MEM_REMOVE to MF_MEM_PRE_REMOVE
>   2. hold s_umount before sync_filesystem()
>   3. move sync_filesystem() after SB_BORN check
>   4. Rebased on next-20220714
> 
> Changes since v4:
>   1. sync_filesystem() at the beginning when MF_MEM_REMOVE
>   2. Rebased on next-20220706
> 
> [1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@dwillia2-desk3.amr.corp.intel.com/
> 
> Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>

Looks reasonable to me now,
Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D

> ---
>  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 69d9c83ea4b2..6da6747435eb 100644
> --- a/fs/xfs/xfs_notify_failure.c
> +++ b/fs/xfs/xfs_notify_failure.c
> @@ -76,6 +76,9 @@ 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;
>  		xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
>  		return -EFSCORRUPTED;
>  	}
> @@ -174,12 +177,22 @@ 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)) {
>  		xfs_warn(mp, "filesystem is not ready for notify_failure()!");
>  		return -EIO;
>  	}
>  
> +	if (mf_flags & MF_MEM_PRE_REMOVE) {
> +		xfs_info(mp, "device is about to be removed!");
> +		down_write(&mp->m_super->s_umount);
> +		error = sync_filesystem(mp->m_super);
> +		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!");
> @@ -188,6 +201,8 @@ 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 4287bec50c28..2ddfb76c8a83 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3188,6 +3188,7 @@ enum mf_flags {
>  	MF_SOFT_OFFLINE = 1 << 3,
>  	MF_UNPOISON = 1 << 4,
>  	MF_SW_SIMULATED = 1 << 5,
> +	MF_MEM_PRE_REMOVE = 1 << 6,
>  };
>  int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
>  		      unsigned long count, int mf_flags);
> -- 
> 2.37.0