[RFC PATCH v5] mm, pmem, xfs: Introduce MF_MEM_REMOVE for unbind

ruansy.fnst
2022-07-08T05:42:31Z

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_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.

==
Changes since v4:
1. sync_filesystem() at the beginning when MF_MEM_REMOVE
2. Rebased on next-20220706

Changes since v3:
1. Flush dirty files and logs when pmem is about to be removed.
2. Rebased on next-20220701

Changes since v2:
1. Rebased on next-20220615

Changes since v1:
1. Drop the needless change of moving {kill,put}_dax()
2. Rebased on '[PATCHSETS] v14 fsdax-rmap + v11 fsdax-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/20220508143620.1775214-1-ruansy.fnst@fujitsu.com/

Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
---
drivers/dax/super.c | 2 +-
fs/xfs/xfs_notify_failure.c | 16 ++++++++++++++++
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..d4bc83159d46 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -323,7 +323,7 @@ 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/fs/xfs/xfs_notify_failure.c b/fs/xfs/xfs_notify_failure.c
index aa8dc27c599c..728b0c1d0ddf 100644
--- a/fs/xfs/xfs_notify_failure.c
+++ b/fs/xfs/xfs_notify_failure.c
@@ -18,6 +18,7 @@
#include "xfs_rmap_btree.h"
#include "xfs_rtalloc.h"
#include "xfs_trans.h"
+#include "xfs_log.h"

#include <linux/mm.h>
#include <linux/dax.h>
@@ -75,6 +76,10 @@ 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_REMOVE) {
+ return 0;
+ }
xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
return -EFSCORRUPTED;
}
@@ -168,6 +173,14 @@ xfs_dax_notify_failure(
struct xfs_mount *mp = dax_holder(dax_dev);
u64 ddev_start;
u64 ddev_end;
+ int error;
+
+ if (mf_flags & MF_MEM_REMOVE) {
+ xfs_info(mp, "device is about to be removed!");
+ error = sync_filesystem(mp->m_super);
+ if (error)
+ return error;
+ }

if (!(mp->m_sb.sb_flags & SB_BORN)) {
xfs_warn(mp, "filesystem is not ready for notify_failure()!");
@@ -182,6 +195,9 @@ 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 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 794ad19b57f8..3eab2d7ba884 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -3240,6 +3240,7 @@ enum mf_flags {
MF_UNPOISON = 1 << 4,
MF_SW_SIMULATED = 1 << 5,
MF_NO_RETRY = 1 << 6,
+ MF_MEM_REMOVE = 1 << 7,
};
int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
unsigned long count, int mf_flags);
--
2.37.0