Re: [RFC PATCH v6] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

Darrick J. Wong
2022-07-14T17:54:22Z

On Thu, Jul 14, 2022 at 10:34:29AM +0000, ruansy.fnst@fujitsu.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@fujitsu.com>

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