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