On Thu, Jun 29, 2023 at 04:16:51PM +0800, Shiyang Ruan 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
> 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()
> -> kill_dax()
> -> dax_holder_notify_failure(dax_dev, 0, U64_MAX, MF_MEM_PRE_REMOVE)
> -> xfs_dax_notify_failure()
> `-> freeze_super() // freeze (kernel call)
> `-> do xfs rmap
> ` -> mf_dax_kill_procs()
> ` -> collect_procs_fsdax() // all associated processes
> ` -> unmap_and_kill()
> ` -> invalidate_inode_pages2_range() // drop file's cache
> `-> thaw_super() // thaw (both kernel & user call)
>
> Introduce MF_MEM_PRE_REMOVE to let filesystem know this is a remove
> event. Use the exclusive freeze/thaw[2] to lock the filesystem to prevent
> new dax mapping from being created. Do not shutdown filesystem directly
> if configuration is not supported, or if failure range includes metadata
> area. Make sure all files and processes(not only the current progress)
> are handled correctly. Also drop the cache of associated files before
> pmem is removed.
>
> [1]:
> https://lore.kernel.org/linux-mm/161604050314.1463742.14151665140035795571.st...@dwillia2-desk3.amr.corp.intel.com/
> [2]:
> https://lore.kernel.org/linux-xfs/168688010689.860947.1788875898367401950.stgit@frogsfrogsfrogs/
>
> Signed-off-by: Shiyang Ruan <[email protected]>
> ---
> drivers/dax/super.c | 3 +-
> fs/xfs/xfs_notify_failure.c | 86 ++++++++++++++++++++++++++++++++++---
> include/linux/mm.h | 1 +
> mm/memory-failure.c | 17 ++++++--
> 4 files changed, 96 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index c4c4728a36e4..2e1a35e82fce 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 4a9bbd3fe120..f6ec56b76db6 100644
> --- a/fs/xfs/xfs_notify_failure.c
> +++ b/fs/xfs/xfs_notify_failure.c
> @@ -22,6 +22,7 @@
>
> #include <linux/mm.h>
> #include <linux/dax.h>
> +#include <linux/fs.h>
>
> struct xfs_failure_info {
> xfs_agblock_t startblock;
> @@ -73,10 +74,16 @@ xfs_dax_failure_fn(
> struct xfs_mount *mp = cur->bc_mp;
> struct xfs_inode *ip;
> struct xfs_failure_info *notify = data;
> + struct address_space *mapping;
> + pgoff_t pgoff;
> + unsigned long pgcnt;
> int error = 0;
>
> if (XFS_RMAP_NON_INODE_OWNER(rec->rm_owner) ||
> (rec->rm_flags & (XFS_RMAP_ATTR_FORK | XFS_RMAP_BMBT_BLOCK))) {
> + /* Continue the query because this isn't a failure. */
> + if (notify->mf_flags & MF_MEM_PRE_REMOVE)
> + return 0;
> notify->want_shutdown = true;
> return 0;
> }
> @@ -92,14 +99,55 @@ xfs_dax_failure_fn(
> return 0;
> }
>
> - error = mf_dax_kill_procs(VFS_I(ip)->i_mapping,
> - xfs_failure_pgoff(mp, rec, notify),
> - xfs_failure_pgcnt(mp, rec, notify),
> - notify->mf_flags);
> + mapping = VFS_I(ip)->i_mapping;
> + pgoff = xfs_failure_pgoff(mp, rec, notify);
> + pgcnt = xfs_failure_pgcnt(mp, rec, notify);
> +
> + /* Continue the rmap query if the inode isn't a dax file. */
> + if (dax_mapping(mapping))
> + error = mf_dax_kill_procs(mapping, pgoff, pgcnt,
> + notify->mf_flags);
> +
> + /* Invalidate the cache in dax pages. */
> + if (notify->mf_flags & MF_MEM_PRE_REMOVE)
> + invalidate_inode_pages2_range(mapping, pgoff,
> + pgoff + pgcnt - 1);
> +
> xfs_irele(ip);
> return error;
> }
>
> +static void
> +xfs_dax_notify_failure_freeze(
> + struct xfs_mount *mp)
> +{
> + struct super_block *sb = mp->m_super;
Nit: extra space right ^ here.
> +
> + /* Wait until no one is holding the FREEZE_HOLDER_KERNEL. */
> + while (freeze_super(sb, FREEZE_HOLDER_KERNEL) != 0) {
> + // Shall we just wait, or print warning then return -EBUSY?
Hm. PRE_REMOVE gets called before the pmem gets unplugged, right? So
we'll send a second notification after it goes away, right?
If so, then I'd say return the error here instead of looping, and live
with a kernel-frozen fs discarding the PRE_REMOVE message.
> + delay(HZ / 10);
> + }
> +}
> +
> +static void
> +xfs_dax_notify_failure_thaw(
> + struct xfs_mount *mp)
> +{
> + struct super_block *sb = mp->m_super;
> + int error;
> +
> + error = thaw_super(sb, FREEZE_HOLDER_KERNEL);
> + if (error)
> + xfs_emerg(mp, "still frozen after notify failure, err=%d",
> + error);
> + /*
> + * Also thaw userspace call anyway because the device is about to be
> + * removed immediately.
> + */
> + thaw_super(sb, FREEZE_HOLDER_USERSPACE);
> +}
> +
> static int
> xfs_dax_notify_ddev_failure(
> struct xfs_mount *mp,
> @@ -120,7 +168,7 @@ xfs_dax_notify_ddev_failure(
>
> error = xfs_trans_alloc_empty(mp, &tp);
> if (error)
> - return error;
> + goto out;
>
> for (; agno <= end_agno; agno++) {
> struct xfs_rmap_irec ri_low = { };
> @@ -165,11 +213,23 @@ xfs_dax_notify_ddev_failure(
> }
>
> xfs_trans_cancel(tp);
> +
> + /*
> + * Determine how to shutdown the filesystem according to the
> + * error code and flags.
> + */
> if (error || notify.want_shutdown) {
> xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_ONDISK);
> if (!error)
> error = -EFSCORRUPTED;
> - }
> + } else if (mf_flags & MF_MEM_PRE_REMOVE)
> + xfs_force_shutdown(mp, SHUTDOWN_FORCE_UMOUNT);
> +
> +out:
> + /* Thaw the fs if it is freezed before. */
> + if (mf_flags & MF_MEM_PRE_REMOVE)
> + xfs_dax_notify_failure_thaw(mp);
_thaw should be called from the same function that called _freeze.
The rest of the patch seems ok to me.
--D
> +
> return error;
> }
>
> @@ -197,6 +257,8 @@ 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;
> @@ -210,6 +272,12 @@ xfs_dax_notify_failure(
> ddev_start = mp->m_ddev_targp->bt_dax_part_off;
> ddev_end = ddev_start + bdev_nr_bytes(mp->m_ddev_targp->bt_bdev) - 1;
>
> + /* Notify failure on the whole device. */
> + if (offset == 0 && len == U64_MAX) {
> + offset = ddev_start;
> + len = bdev_nr_bytes(mp->m_ddev_targp->bt_bdev);
> + }
> +
> /* Ignore the range out of filesystem area */
> if (offset + len - 1 < ddev_start)
> return -ENXIO;
> @@ -226,6 +294,12 @@ xfs_dax_notify_failure(
> if (offset + len - 1 > ddev_end)
> len = ddev_end - offset + 1;
>
> + if (mf_flags & MF_MEM_PRE_REMOVE) {
> + xfs_info(mp, "device is about to be removed!");
> + /* Freeze fs to prevent new mappings from being created. */
> + xfs_dax_notify_failure_freeze(mp);
> + }
> +
> return xfs_dax_notify_ddev_failure(mp, BTOBB(offset), BTOBB(len),
> mf_flags);
> }
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 27ce77080c79..a80c255b88d2 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3576,6 +3576,7 @@ enum mf_flags {
> MF_UNPOISON = 1 << 4,
> MF_SW_SIMULATED = 1 << 5,
> MF_NO_RETRY = 1 << 6,
> + MF_MEM_PRE_REMOVE = 1 << 7,
> };
> int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
> unsigned long count, int mf_flags);
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 5b663eca1f29..483b75f2fcfb 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -688,7 +688,7 @@ static void add_to_kill_fsdax(struct task_struct *tsk,
> struct page *p,
> */
> static void collect_procs_fsdax(struct page *page,
> struct address_space *mapping, pgoff_t pgoff,
> - struct list_head *to_kill)
> + struct list_head *to_kill, bool pre_remove)
> {
> struct vm_area_struct *vma;
> struct task_struct *tsk;
> @@ -696,8 +696,15 @@ static void collect_procs_fsdax(struct page *page,
> i_mmap_lock_read(mapping);
> read_lock(&tasklist_lock);
> for_each_process(tsk) {
> - struct task_struct *t = task_early_kill(tsk, true);
> + struct task_struct *t = tsk;
>
> + /*
> + * Search for all tasks while MF_MEM_PRE_REMOVE, because the
> + * current may not be the one accessing the fsdax page.
> + * Otherwise, search for the current task.
> + */
> + if (!pre_remove)
> + t = task_early_kill(tsk, true);
> if (!t)
> continue;
> vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
> @@ -1793,6 +1800,7 @@ int mf_dax_kill_procs(struct address_space *mapping,
> pgoff_t index,
> dax_entry_t cookie;
> struct page *page;
> size_t end = index + count;
> + bool pre_remove = mf_flags & MF_MEM_PRE_REMOVE;
>
> mf_flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
>
> @@ -1804,9 +1812,10 @@ int mf_dax_kill_procs(struct address_space *mapping,
> pgoff_t index,
> if (!page)
> goto unlock;
>
> - SetPageHWPoison(page);
> + if (!pre_remove)
> + SetPageHWPoison(page);
>
> - collect_procs_fsdax(page, mapping, index, &to_kill);
> + collect_procs_fsdax(page, mapping, index, &to_kill, pre_remove);
> unmap_and_kill(&to_kill, page_to_pfn(page), mapping,
> index, mf_flags);
> unlock:
> --
> 2.40.1
>
