Re: [PATCH v4 05/10] mm, pmem: Implement ->memory_failure() in pmem driver

Dan Williams
2021-06-16T06:50:17Z

On Thu, Jun 3, 2021 at 6:19 PM Shiyang Ruan <ruansy.fnst@fujitsu.com> wrote:
>
> Call the ->memory_failure() which is implemented by pmem driver, in
> order to finally notify filesystem to handle the corrupted data. The
> handler which collects and kills processes are moved into
> mf_dax_kill_procs(), which will be called by filesystem.
>
> Keep the old handler in order to roll back if driver or filesystem
> does not support ->memory_failure()/->corrupted_range().
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> ---
> block/genhd.c | 30 ++++++++++++++++++
> drivers/nvdimm/pmem.c | 14 +++++++++
> include/linux/genhd.h | 1 +
> mm/memory-failure.c | 71 +++++++++++++++++++++++++++----------------

I would not expect a patch that converts the pmem driver to touch
mm/memory-failure.c. mf_generic_kill_procs() has nothing to do with
the pmem driver.

> 4 files changed, 90 insertions(+), 26 deletions(-)
>
> diff --git a/block/genhd.c b/block/genhd.c
> index 9f8cb7beaad1..75834bd057df 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -718,6 +718,36 @@ struct block_device *bdget_disk(struct gendisk *disk, int partno)
> return bdev;
> }
>
> +/**
> + * bdget_disk_sector - get block device by given sector number
> + * @disk: gendisk of interest
> + * @sector: sector number
> + *
> + * RETURNS: the found block device where sector locates in
> + */
> +struct block_device *bdget_disk_sector(struct gendisk *disk, sector_t sector)
> +{
> + struct block_device *part = NULL, *p;
> + unsigned long idx;
> +
> + rcu_read_lock();
> + xa_for_each(&disk->part_tbl, idx, p) {
> + if (p->bd_partno == 0)
> + continue;
> + if (p->bd_start_sect <= sector &&
> + sector < p->bd_start_sect + bdev_nr_sectors(p)) {
> + part = p;
> + break;
> + }
> + }
> + rcu_read_unlock();
> + if (!part)
> + part = disk->part0;
> +
> + return bdget_disk(disk, part->bd_partno);
> +}
> +EXPORT_SYMBOL(bdget_disk_sector);

I can't see any justification for this function. The pmem driver does
not need it and the upper layer holders should have their own
mechanism to go from dax_dev offset to bdev if they need to, but
hopefully they don't. A dax_device failure should be independent of a
block_device failure.

> +
> /*
> * print a full list of all partitions - intended for places where the root
> * filesystem can't be mounted and thus to give the victim some idea of what
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index ed10a8b66068..98349e7d0a28 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -364,9 +364,23 @@ static void pmem_release_disk(void *__pmem)
> put_disk(pmem->disk);
> }
>
> +static int pmem_pagemap_memory_failure(struct dev_pagemap *pgmap,
> + unsigned long pfn, int flags)
> +{
> + struct pmem_device *pdev =
> + container_of(pgmap, struct pmem_device, pgmap);

This local variable is called @pmem not @pdev in other parts of the driver.

> + loff_t offset = PFN_PHYS(pfn) - pdev->phys_addr - pdev->data_offset;
> + struct block_device *bdev =
> + bdget_disk_sector(pdev->disk, offset >> SECTOR_SHIFT);
> +
> + return dax_corrupted_range(pdev->dax_dev, bdev, offset,
> + page_size(pfn_to_page(pfn)), &flags);

Per previous comments this interface should be range based. Why is the
last argument &flags? That was passed in by value so any changes to it
will not be reflected back to memory_failure()?

> +}
> +
> static const struct dev_pagemap_ops fsdax_pagemap_ops = {
> .kill = pmem_pagemap_kill,
> .cleanup = pmem_pagemap_cleanup,
> + .memory_failure = pmem_pagemap_memory_failure,
> };
>
> static int pmem_attach_disk(struct device *dev,
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index 6fc26f7bdf71..2ad70c02c343 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -219,6 +219,7 @@ static inline void add_disk_no_queue_reg(struct gendisk *disk)
>
> extern void del_gendisk(struct gendisk *gp);
> extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
> +extern struct block_device *bdget_disk_sector(struct gendisk *disk, sector_t sector);
>
> void set_disk_ro(struct gendisk *disk, bool read_only);
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 4377e727d478..43017d7f3918 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -1247,6 +1247,36 @@ static void unmap_and_kill(struct list_head *to_kill, unsigned long pfn,
> kill_procs(to_kill, flags & MF_MUST_KILL, false, pfn, flags);
> }
>
> +static int mf_generic_kill_procs(unsigned long long pfn, int flags)
> +{
> + struct page *page = pfn_to_page(pfn);
> + LIST_HEAD(to_kill);
> + dax_entry_t cookie;
> +
> + /*
> + * Prevent the inode from being freed while we are interrogating
> + * the address_space, typically this would be handled by
> + * lock_page(), but dax pages do not use the page lock. This
> + * also prevents changes to the mapping of this pfn until
> + * poison signaling is complete.
> + */
> + cookie = dax_lock_page(page);
> + if (!cookie)
> + return -EBUSY;
> + /*
> + * Unlike System-RAM there is no possibility to swap in a
> + * different physical page at a given virtual address, so all
> + * userspace consumption of ZONE_DEVICE memory necessitates
> + * SIGBUS (i.e. MF_MUST_KILL)
> + */
> + flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
> + collect_procs(page, &to_kill, flags & MF_ACTION_REQUIRED);
> +
> + unmap_and_kill(&to_kill, pfn, page->mapping, page->index, flags);
> + dax_unlock_page(page, cookie);
> + return 0;
> +}
> +

Per above, I am surprised to find this in this patch, it belong in its
own patch if at all.

> int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index, int flags)
> {
> LIST_HEAD(to_kill);
> @@ -1348,9 +1378,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> struct dev_pagemap *pgmap)
> {
> struct page *page = pfn_to_page(pfn);
> - LIST_HEAD(to_kill);
> int rc = -EBUSY;
> - dax_entry_t cookie;
>
> if (flags & MF_COUNT_INCREASED)
> /*
> @@ -1364,20 +1392,9 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> goto out;
> }
>
> - /*
> - * Prevent the inode from being freed while we are interrogating
> - * the address_space, typically this would be handled by
> - * lock_page(), but dax pages do not use the page lock. This
> - * also prevents changes to the mapping of this pfn until
> - * poison signaling is complete.
> - */
> - cookie = dax_lock_page(page);
> - if (!cookie)
> - goto out;
> -
> if (hwpoison_filter(page)) {
> rc = 0;
> - goto unlock;
> + goto out;
> }
>
> if (pgmap->type == MEMORY_DEVICE_PRIVATE) {
> @@ -1385,7 +1402,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> * TODO: Handle HMM pages which may need coordination
> * with device-side memory.
> */
> - goto unlock;
> + goto out;
> }
>
> /*
> @@ -1395,19 +1412,21 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
> SetPageHWPoison(page);
>
> /*
> - * Unlike System-RAM there is no possibility to swap in a
> - * different physical page at a given virtual address, so all
> - * userspace consumption of ZONE_DEVICE memory necessitates
> - * SIGBUS (i.e. MF_MUST_KILL)
> + * Call driver's implementation to handle the memory failure,
> + * otherwise roll back to generic handler.
> */
> - flags |= MF_ACTION_REQUIRED | MF_MUST_KILL;
> - collect_procs_file(page, page->mapping, page->index, &to_kill,
> - flags & MF_ACTION_REQUIRED);
> + if (pgmap->ops->memory_failure) {
> + rc = pgmap->ops->memory_failure(pgmap, pfn, flags);
> + /*
> + * Roll back to generic handler too if operation is not
> + * supported inside the driver/device/filesystem.
> + */
> + if (rc != EOPNOTSUPP)
> + goto out;
> + }
> +
> + rc = mf_generic_kill_procs(pfn, flags);
>
> - unmap_and_kill(&to_kill, pfn, page->mapping, page->index, flags);
> - rc = 0;
> -unlock:
> - dax_unlock_page(page, cookie);
> out:
> /* drop pgmap ref acquired in caller */
> put_dev_pagemap(pgmap);
> --
> 2.31.1
>
>
>