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

Shiyang Ruan
2022-04-10T17:16:38Z

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)
-> pmem driver ->remove()
-> kill_dax()
-> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_REMOVE)
-> xfs_dax_notify_failure()

Introduce MF_MEM_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.

Based on "[PATCH v12] fsdax: introduce fs query to support reflink"[2]

[1]: https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.stgit@dwillia2-desk3.amr.corp.intel.com/
[2]: https://lore.kernel.org/linux-xfs/20220410160904.3758789-1-ruansy.fnst@fujitsu.com/T/#t

Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
---
drivers/dax/super.c | 2 +-
drivers/nvdimm/pmem.c | 3 ++-
fs/xfs/xfs_notify_failure.c | 6 +++++-
include/linux/mm.h | 1 +
4 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 619a05615497..52f820fdd8ff 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -312,7 +312,7 @@ 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_REMOVE);

clear_bit(DAXDEV_ALIVE, &dax_dev->flags);
synchronize_srcu(&dax_srcu);
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index bd502957cfdf..72d9e69aea98 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -359,7 +359,6 @@ static void pmem_release_disk(void *__pmem)
struct pmem_device *pmem = __pmem;

dax_remove_host(pmem->disk);
- kill_dax(pmem->dax_dev);
put_dax(pmem->dax_dev);
del_gendisk(pmem->disk);

@@ -597,6 +596,8 @@ static void nd_pmem_remove(struct device *dev)
pmem->bb_state = NULL;
}
nvdimm_flush(to_nd_region(dev->parent), NULL);
+
+ kill_dax(pmem->dax_dev);
}

static void nd_pmem_shutdown(struct device *dev)
diff --git a/fs/xfs/xfs_notify_failure.c b/fs/xfs/xfs_notify_failure.c
index aac44f54feb4..f8b41085218b 100644
--- a/fs/xfs/xfs_notify_failure.c
+++ b/fs/xfs/xfs_notify_failure.c
@@ -73,7 +73,9 @@ xfs_dax_failure_fn(
struct failure_info *notify = data;
int error = 0;

- if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
+ /* Do not shutdown so early when device is to be removed */
+ if (!(notify->mf_flags & MF_MEM_REMOVE) ||
+ XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
(rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) {
xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
return -EFSCORRUPTED;
@@ -181,6 +183,8 @@ 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_REMOVE)
+ return -EOPNOTSUPP;
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 742604feef28..b47c3745782d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3225,6 +3225,7 @@ enum mf_flags {
MF_MUST_KILL = 1 << 2,
MF_SOFT_OFFLINE = 1 << 3,
MF_UNPOISON = 1 << 4,
+ MF_MEM_REMOVE = 1 << 5,
};
int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
unsigned long count, int mf_flags);
--
2.35.1