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[PATCH v6 0/5] dax: handling media errors (clear-on-zero only)

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  [PATCH v6 0/5] dax: handling media errors (clear-on-zero only) Vishal Verma <vishal.l.verma@intel.com> - 2016-05-10 21:00 +0200
    [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible Vishal Verma <vishal.l.verma@intel.com> - 2016-05-10 21:00 +0200
      Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through  the driver if possible Christoph Hellwig <hch@infradead.org> - 2016-05-10 21:30 +0200
        Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through  the driver if possible "Verma, Vishal L" <vishal.l.verma@intel.com> - 2016-05-10 21:50 +0200
      Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through  the driver if possible Jan Kara <jack@suse.cz> - 2016-05-11 10:20 +0200
        Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through  the driver if possible "Verma, Vishal L" <vishal.l.verma@intel.com> - 2016-05-11 19:50 +0200
      Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through  the driver if possible "Verma, Vishal L" <vishal.l.verma@intel.com> - 2016-05-11 20:50 +0200
    [PATCH v6 2/5] dax: enable dax in the presence of known media errors (badblocks) Vishal Verma <vishal.l.verma@intel.com> - 2016-05-10 21:00 +0200
    [PATCH v6 5/5] dax: fix a comment in dax_zero_page_range and dax_truncate_page Vishal Verma <vishal.l.verma@intel.com> - 2016-05-10 21:00 +0200
    [PATCH v6 3/5] dax: use sb_issue_zerout instead of calling dax_clear_sectors Vishal Verma <vishal.l.verma@intel.com> - 2016-05-10 21:00 +0200

#1398403 — [PATCH v6 0/5] dax: handling media errors (clear-on-zero only)

Until now, dax has been disabled if media errors were found on
any device. This series attempts to address that.

The first two patches from Dan re-enable dax even when media
errors are present.

The third patch from Matthew removes the zeroout path from dax
entirely, making zeroout operations always go through the driver
(The motivation is that if a backing device has media errors,
and we create a sparse file on it, we don't want the initial
zeroing to happen via dax, we want to give the block driver a
chance to clear the errors).

Patch 4 reduces our calls to clear_pmem from dax in the
truncate/hole-punch cases. We check if the range being truncated
is sector aligned/sized, and if so, send blkdev_issue_zeroout
instead of clear_pmem so that errors can be handled better by
the driver.

Patch 5 fixes a redundant comment in DAX and is mostly unrelated
to the rest of this series.

This series also depends on/is based on Jan Kara's DAX Locking
fixes series [1].


[1]: http://www.spinics.net/lists/linux-mm/msg105819.html

v6:
 - Use IS_ALIGNED in dax_range_is_aligned instead of open coding
   an alignment check (Jan)
 - Collect all Reveiwed-by tags so far.

v5:
 - Drop the patch that attempts to clear-errors-on-write till we
   reach consensus on how to handle that.
 - Don't pass blk_dax_ctl to direct_access, instead pass in all the
   required arguments individually (Christoph, Dan)

v4:
 - Remove the dax->direct_IO fallbacks entirely. Instead, go through
   the usual direct_IO path when we're in O_DIRECT, and use dax_IO
   for other, non O_DIRECT IO. (Dan, Christoph)

v3:
 - Wrapper-ize the direct_IO fallback again and make an exception
   for -EIOCBQUEUED (Jeff, Dan)
 - Reduce clear_pmem usage in DAX to the minimum


Dan Williams (2):
  dax: fallback from pmd to pte on error
  dax: enable dax in the presence of known media errors (badblocks)

Matthew Wilcox (1):
  dax: use sb_issue_zerout instead of calling dax_clear_sectors

Vishal Verma (2):
  dax: for truncate/hole-punch, do zeroing through the driver if
    possible
  dax: fix a comment in dax_zero_page_range and dax_truncate_page

 Documentation/filesystems/dax.txt | 32 ++++++++++++++++
 arch/powerpc/sysdev/axonram.c     |  2 +-
 block/ioctl.c                     |  9 -----
 drivers/block/brd.c               |  2 +-
 drivers/nvdimm/pmem.c             | 10 ++++-
 drivers/s390/block/dcssblk.c      |  2 +-
 fs/block_dev.c                    |  2 +-
 fs/dax.c                          | 77 +++++++++++++--------------------------
 fs/ext2/inode.c                   |  7 ++--
 fs/xfs/xfs_bmap_util.c            | 15 ++------
 include/linux/blkdev.h            |  2 +-
 include/linux/dax.h               |  1 -
 12 files changed, 79 insertions(+), 82 deletions(-)

-- 
2.5.5

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#1398407 — [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible

In the truncate or hole-punch path in dax, we clear out sub-page ranges.
If these sub-page ranges are sector aligned and sized, we can do the
zeroing through the driver instead so that error-clearing is handled
automatically.

For sub-sector ranges, we still have to rely on clear_pmem and have the
possibility of tripping over errors.

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 Documentation/filesystems/dax.txt | 32 ++++++++++++++++++++++++++++++++
 fs/dax.c                          | 29 ++++++++++++++++++++++++-----
 2 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
index 7bde640..ce4587d 100644
--- a/Documentation/filesystems/dax.txt
+++ b/Documentation/filesystems/dax.txt
@@ -79,6 +79,38 @@ These filesystems may be used for inspiration:
 - ext4: the fourth extended filesystem, see Documentation/filesystems/ext4.txt
 
 
+Handling Media Errors
+---------------------
+
+The libnvdimm subsystem stores a record of known media error locations for
+each pmem block device (in gendisk->badblocks). If we fault at such location,
+or one with a latent error not yet discovered, the application can expect
+to receive a SIGBUS. Libnvdimm also allows clearing of these errors by simply
+writing the affected sectors (through the pmem driver, and if the underlying
+NVDIMM supports the clear_poison DSM defined by ACPI).
+
+Since DAX IO normally doesn't go through the driver/bio path, applications or
+sysadmins have an option to restore the lost data from a prior backup/inbuilt
+redundancy in the following ways:
+
+1. Delete the affected file, and restore from a backup (sysadmin route):
+   This will free the file system blocks that were being used by the file,
+   and the next time they're allocated, they will be zeroed first, which
+   happens through the driver, and will clear bad sectors.
+
+2. Truncate or hole-punch the part of the file that has a bad-block (at least
+   an entire aligned sector has to be hole-punched, but not necessarily an
+   entire filesystem block).
+
+These are the two basic paths that allow DAX filesystems to continue operating
+in the presence of media errors. More robust error recovery mechanisms can be
+built on top of this in the future, for example, involving redundancy/mirroring
+provided at the block layer through DM, or additionally, at the filesystem
+level. These would have to rely on the above two tenets, that error clearing
+can happen either by sending an IO through the driver, or zeroing (also through
+the driver).
+
+
 Shortcomings
 ------------
 
diff --git a/fs/dax.c b/fs/dax.c
index 5948d9b..0167cde 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1196,6 +1196,20 @@ out:
 }
 EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
 
+static bool dax_range_is_aligned(struct block_device *bdev,
+				 struct blk_dax_ctl *dax, unsigned int offset,
+				 unsigned int length)
+{
+	unsigned short sector_size = bdev_logical_block_size(bdev);
+
+	if (!IS_ALIGNED(((u64)dax->addr + offset), sector_size))
+		return false;
+	if (!IS_ALIGNED(length, sector_size))
+		return false;
+
+	return true;
+}
+
 /**
  * dax_zero_page_range - zero a range within a page of a DAX file
  * @inode: The file being truncated
@@ -1240,11 +1254,16 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
 			.size = PAGE_SIZE,
 		};
 
-		if (dax_map_atomic(bdev, &dax) < 0)
-			return PTR_ERR(dax.addr);
-		clear_pmem(dax.addr + offset, length);
-		wmb_pmem();
-		dax_unmap_atomic(bdev, &dax);
+		if (dax_range_is_aligned(bdev, &dax, offset, length))
+			return blkdev_issue_zeroout(bdev, dax.sector,
+					length >> 9, GFP_NOFS, true);
+		else {
+			if (dax_map_atomic(bdev, &dax) < 0)
+				return PTR_ERR(dax.addr);
+			clear_pmem(dax.addr + offset, length);
+			wmb_pmem();
+			dax_unmap_atomic(bdev, &dax);
+		}
 	}
 
 	return 0;
-- 
2.5.5

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#1398445 — Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible

Hi Vishal,

can you also pick up the my patch to add a low-level __dax_zero_range
that I cced you on?  That way we can avoid a nasty merge conflict with
my xfs/iomap changes.

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#1398450 — Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible

On Tue, 2016-05-10 at 12:25 -0700, Christoph Hellwig wrote:
> Hi Vishal,
> 
> can you also pick up the my patch to add a low-level __dax_zero_range
> that I cced you on?  That way we can avoid a nasty merge conflict with
> my xfs/iomap changes.

Good idea - I'll do that for the next posting. I'll wait a day or two
for any additional reviews/acks.

I'm looking to get all this into a branch in the nvdimm tree once Jan
splits up his dax-locking series..

Mostly I guess I'm looking for a yay or nay for the block layer changes
(patch 2). Jens?

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#1398761 — Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible

On Tue 10-05-16 12:49:15, Vishal Verma wrote:
> In the truncate or hole-punch path in dax, we clear out sub-page ranges.
> If these sub-page ranges are sector aligned and sized, we can do the
> zeroing through the driver instead so that error-clearing is handled
> automatically.
> 
> For sub-sector ranges, we still have to rely on clear_pmem and have the
> possibility of tripping over errors.
> 
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> Cc: Jeff Moyer <jmoyer@redhat.com>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Jan Kara <jack@suse.cz>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

...

> +static bool dax_range_is_aligned(struct block_device *bdev,
> +				 struct blk_dax_ctl *dax, unsigned int offset,
> +				 unsigned int length)
> +{
> +	unsigned short sector_size = bdev_logical_block_size(bdev);
> +
> +	if (!IS_ALIGNED(((u64)dax->addr + offset), sector_size))

One more question: 'dax' is initialized in dax_zero_page_range() and
dax->addr is going to be always NULL here. So either you forgot to call
dax_map_atomic() to get the addr or the use of dax->addr is just bogus
(which is what I currently believe since I see no way how the address could
be unaligned with the sector_size)...

								Honza
> +		return false;
> +	if (!IS_ALIGNED(length, sector_size))
> +		return false;
> +
> +	return true;
> +}
> +
>  /**
>   * dax_zero_page_range - zero a range within a page of a DAX file
>   * @inode: The file being truncated
> @@ -1240,11 +1254,16 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
>  			.size = PAGE_SIZE,
>  		};
>  
> -		if (dax_map_atomic(bdev, &dax) < 0)
> -			return PTR_ERR(dax.addr);
> -		clear_pmem(dax.addr + offset, length);
> -		wmb_pmem();
> -		dax_unmap_atomic(bdev, &dax);
> +		if (dax_range_is_aligned(bdev, &dax, offset, length))
> +			return blkdev_issue_zeroout(bdev, dax.sector,
> +					length >> 9, GFP_NOFS, true);
> +		else {
> +			if (dax_map_atomic(bdev, &dax) < 0)
> +				return PTR_ERR(dax.addr);
> +			clear_pmem(dax.addr + offset, length);
> +			wmb_pmem();
> +			dax_unmap_atomic(bdev, &dax);
> +		}
>  	}
>  
>  	return 0;
> -- 
> 2.5.5
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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#1399389 — Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible

On Wed, 2016-05-11 at 10:15 +0200, Jan Kara wrote:
> On Tue 10-05-16 12:49:15, Vishal Verma wrote:
> > 
> > In the truncate or hole-punch path in dax, we clear out sub-page
> > ranges.
> > If these sub-page ranges are sector aligned and sized, we can do the
> > zeroing through the driver instead so that error-clearing is handled
> > automatically.
> > 
> > For sub-sector ranges, we still have to rely on clear_pmem and have
> > the
> > possibility of tripping over errors.
> > 
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
> > Cc: Jeff Moyer <jmoyer@redhat.com>
> > Cc: Christoph Hellwig <hch@infradead.org>
> > Cc: Dave Chinner <david@fromorbit.com>
> > Cc: Jan Kara <jack@suse.cz>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
> ...
> 
> > 
> > +static bool dax_range_is_aligned(struct block_device *bdev,
> > +				 struct blk_dax_ctl *dax, unsigned
> > int offset,
> > +				 unsigned int length)
> > +{
> > +	unsigned short sector_size = bdev_logical_block_size(bdev);
> > +
> > +	if (!IS_ALIGNED(((u64)dax->addr + offset), sector_size))
> One more question: 'dax' is initialized in dax_zero_page_range() and
> dax->addr is going to be always NULL here. So either you forgot to
> call
> dax_map_atomic() to get the addr or the use of dax->addr is just bogus
> (which is what I currently believe since I see no way how the address
> could
> be unaligned with the sector_size)...
> 

Good catch, and you're right. I don't think I actually even want to use
dax->addr for the alignment check here - I want to check if we're
aligned to the block device sector. I'm thinking something like:

	if (!IS_ALIGNED(offset, sector_size))

Technically we want to check if sector * sector_size + offset is
aligned, but the first part of that is already a sector :)

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#1399418 — Re: [PATCH v6 4/5] dax: for truncate/hole-punch, do zeroing through the driver if possible

On Tue, 2016-05-10 at 12:49 -0600, Vishal Verma wrote:
> 
...

> @@ -1240,11 +1254,16 @@ int dax_zero_page_range(struct inode *inode,
> loff_t from, unsigned length,
>  			.size = PAGE_SIZE,
>  		};
>  
> -		if (dax_map_atomic(bdev, &dax) < 0)
> -			return PTR_ERR(dax.addr);
> -		clear_pmem(dax.addr + offset, length);
> -		wmb_pmem();
> -		dax_unmap_atomic(bdev, &dax);
> +		if (dax_range_is_aligned(bdev, &dax, offset, length))
> +			return blkdev_issue_zeroout(bdev, dax.sector,
> +					length >> 9, GFP_NOFS, true);

Found another bug here while testing. The zeroout needs to be done for
sector + (offset >> 9). The above just zeroed out the first sector of
the page irrespective of offset, which is wrong.

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#1398408 — [PATCH v6 2/5] dax: enable dax in the presence of known media errors (badblocks)

From: Dan Williams <dan.j.williams@intel.com>

1/ If a mapping overlaps a bad sector fail the request.

2/ Do not opportunistically report more dax-capable capacity than is
   requested when errors present.

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
[vishal: fix a conflict with system RAM collision patches]
[vishal: add a 'size' parameter to ->direct_access]
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 arch/powerpc/sysdev/axonram.c |  2 +-
 block/ioctl.c                 |  9 ---------
 drivers/block/brd.c           |  2 +-
 drivers/nvdimm/pmem.c         | 10 +++++++++-
 drivers/s390/block/dcssblk.c  |  2 +-
 fs/block_dev.c                |  2 +-
 include/linux/blkdev.h        |  2 +-
 7 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/sysdev/axonram.c b/arch/powerpc/sysdev/axonram.c
index 0d112b9..ff75d70 100644
--- a/arch/powerpc/sysdev/axonram.c
+++ b/arch/powerpc/sysdev/axonram.c
@@ -143,7 +143,7 @@ axon_ram_make_request(struct request_queue *queue, struct bio *bio)
  */
 static long
 axon_ram_direct_access(struct block_device *device, sector_t sector,
-		       void __pmem **kaddr, pfn_t *pfn)
+		       void __pmem **kaddr, pfn_t *pfn, long size)
 {
 	struct axon_ram_bank *bank = device->bd_disk->private_data;
 	loff_t offset = (loff_t)sector << AXON_RAM_SECTOR_SHIFT;
diff --git a/block/ioctl.c b/block/ioctl.c
index 4ff1f92..bf80bfd 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -423,15 +423,6 @@ bool blkdev_dax_capable(struct block_device *bdev)
 			|| (bdev->bd_part->nr_sects % (PAGE_SIZE / 512)))
 		return false;
 
-	/*
-	 * If the device has known bad blocks, force all I/O through the
-	 * driver / page cache.
-	 *
-	 * TODO: support finer grained dax error handling
-	 */
-	if (disk->bb && disk->bb->count)
-		return false;
-
 	return true;
 }
 #endif
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 51a071e..c04bd9b 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -381,7 +381,7 @@ static int brd_rw_page(struct block_device *bdev, sector_t sector,
 
 #ifdef CONFIG_BLK_DEV_RAM_DAX
 static long brd_direct_access(struct block_device *bdev, sector_t sector,
-			void __pmem **kaddr, pfn_t *pfn)
+			void __pmem **kaddr, pfn_t *pfn, long size)
 {
 	struct brd_device *brd = bdev->bd_disk->private_data;
 	struct page *page;
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index f798899..c447579 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -182,14 +182,22 @@ static int pmem_rw_page(struct block_device *bdev, sector_t sector,
 }
 
 static long pmem_direct_access(struct block_device *bdev, sector_t sector,
-		      void __pmem **kaddr, pfn_t *pfn)
+		      void __pmem **kaddr, pfn_t *pfn, long size)
 {
 	struct pmem_device *pmem = bdev->bd_disk->private_data;
 	resource_size_t offset = sector * 512 + pmem->data_offset;
 
+	if (unlikely(is_bad_pmem(&pmem->bb, sector, size)))
+		return -EIO;
 	*kaddr = pmem->virt_addr + offset;
 	*pfn = phys_to_pfn_t(pmem->phys_addr + offset, pmem->pfn_flags);
 
+	/*
+	 * If badblocks are present, limit known good range to the
+	 * requested range.
+	 */
+	if (unlikely(pmem->bb.count))
+		return size;
 	return pmem->size - pmem->pfn_pad - offset;
 }
 
diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
index b839086..c45d538 100644
--- a/drivers/s390/block/dcssblk.c
+++ b/drivers/s390/block/dcssblk.c
@@ -884,7 +884,7 @@ fail:
 
 static long
 dcssblk_direct_access (struct block_device *bdev, sector_t secnum,
-			void __pmem **kaddr, pfn_t *pfn)
+			void __pmem **kaddr, pfn_t *pfn, long size)
 {
 	struct dcssblk_dev_info *dev_info;
 	unsigned long offset, dev_sz;
diff --git a/fs/block_dev.c b/fs/block_dev.c
index b25bb23..02c68c4 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -488,7 +488,7 @@ long bdev_direct_access(struct block_device *bdev, struct blk_dax_ctl *dax)
 	sector += get_start_sect(bdev);
 	if (sector % (PAGE_SIZE / 512))
 		return -EINVAL;
-	avail = ops->direct_access(bdev, sector, &dax->addr, &dax->pfn);
+	avail = ops->direct_access(bdev, sector, &dax->addr, &dax->pfn, size);
 	if (!avail)
 		return -ERANGE;
 	if (avail > 0 && avail & ~PAGE_MASK)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 669e419..55ed530 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1657,7 +1657,7 @@ struct block_device_operations {
 	int (*ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
 	int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
 	long (*direct_access)(struct block_device *, sector_t, void __pmem **,
-			pfn_t *);
+			pfn_t *, long);
 	unsigned int (*check_events) (struct gendisk *disk,
 				      unsigned int clearing);
 	/* ->media_changed() is DEPRECATED, use ->check_events() instead */
-- 
2.5.5

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#1398418 — [PATCH v6 5/5] dax: fix a comment in dax_zero_page_range and dax_truncate_page

The distinction between PAGE_SIZE and PAGE_CACHE_SIZE was removed in

09cbfea mm, fs: get rid of PAGE_CACHE_* and page_cache_{get,release}
macros

The comments for the above functions described a distinction between
those, that is now redundant, so remove those paragraphs

Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 fs/dax.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 0167cde..afa289c 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1221,12 +1221,6 @@ static bool dax_range_is_aligned(struct block_device *bdev,
  * page in a DAX file.  This is intended for hole-punch operations.  If
  * you are truncating a file, the helper function dax_truncate_page() may be
  * more convenient.
- *
- * We work in terms of PAGE_SIZE here for commonality with
- * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
- * took care of disposing of the unnecessary blocks.  Even if the filesystem
- * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
- * since the file might be mmapped.
  */
 int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
 							get_block_t get_block)
@@ -1278,12 +1272,6 @@ EXPORT_SYMBOL_GPL(dax_zero_page_range);
  *
  * Similar to block_truncate_page(), this function can be called by a
  * filesystem when it is truncating a DAX file to handle the partial page.
- *
- * We work in terms of PAGE_SIZE here for commonality with
- * block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
- * took care of disposing of the unnecessary blocks.  Even if the filesystem
- * block size is smaller than PAGE_SIZE, we have to zero the rest of the page
- * since the file might be mmapped.
  */
 int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
 {
-- 
2.5.5

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#1398419 — [PATCH v6 3/5] dax: use sb_issue_zerout instead of calling dax_clear_sectors

From: Matthew Wilcox <matthew.r.wilcox@intel.com>

dax_clear_sectors() cannot handle poisoned blocks.  These must be
zeroed using the BIO interface instead.  Convert ext2 and XFS to use
only sb_issue_zerout().

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
[vishal: Also remove the dax_clear_sectors function entirely]
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
---
 fs/dax.c               | 32 --------------------------------
 fs/ext2/inode.c        |  7 +++----
 fs/xfs/xfs_bmap_util.c | 15 ++++-----------
 include/linux/dax.h    |  1 -
 4 files changed, 7 insertions(+), 48 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 52f0044..5948d9b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -116,38 +116,6 @@ struct page *read_dax_sector(struct block_device *bdev, sector_t n)
 	return page;
 }
 
-/*
- * dax_clear_sectors() is called from within transaction context from XFS,
- * and hence this means the stack from this point must follow GFP_NOFS
- * semantics for all operations.
- */
-int dax_clear_sectors(struct block_device *bdev, sector_t _sector, long _size)
-{
-	struct blk_dax_ctl dax = {
-		.sector = _sector,
-		.size = _size,
-	};
-
-	might_sleep();
-	do {
-		long count, sz;
-
-		count = dax_map_atomic(bdev, &dax);
-		if (count < 0)
-			return count;
-		sz = min_t(long, count, SZ_128K);
-		clear_pmem(dax.addr, sz);
-		dax.size -= sz;
-		dax.sector += sz / 512;
-		dax_unmap_atomic(bdev, &dax);
-		cond_resched();
-	} while (dax.size);
-
-	wmb_pmem();
-	return 0;
-}
-EXPORT_SYMBOL_GPL(dax_clear_sectors);
-
 static bool buffer_written(struct buffer_head *bh)
 {
 	return buffer_mapped(bh) && !buffer_unwritten(bh);
diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 1f07b75..35f2b0bf 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -26,6 +26,7 @@
 #include <linux/highuid.h>
 #include <linux/pagemap.h>
 #include <linux/dax.h>
+#include <linux/blkdev.h>
 #include <linux/quotaops.h>
 #include <linux/writeback.h>
 #include <linux/buffer_head.h>
@@ -737,10 +738,8 @@ static int ext2_get_blocks(struct inode *inode,
 		 * so that it's not found by another thread before it's
 		 * initialised
 		 */
-		err = dax_clear_sectors(inode->i_sb->s_bdev,
-				le32_to_cpu(chain[depth-1].key) <<
-				(inode->i_blkbits - 9),
-				1 << inode->i_blkbits);
+		err = sb_issue_zeroout(inode->i_sb,
+				le32_to_cpu(chain[depth-1].key), 1, GFP_NOFS);
 		if (err) {
 			mutex_unlock(&ei->truncate_mutex);
 			goto cleanup;
diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 3b63098..930ac6a 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -72,18 +72,11 @@ xfs_zero_extent(
 	struct xfs_mount *mp = ip->i_mount;
 	xfs_daddr_t	sector = xfs_fsb_to_db(ip, start_fsb);
 	sector_t	block = XFS_BB_TO_FSBT(mp, sector);
-	ssize_t		size = XFS_FSB_TO_B(mp, count_fsb);
-
-	if (IS_DAX(VFS_I(ip)))
-		return dax_clear_sectors(xfs_find_bdev_for_inode(VFS_I(ip)),
-				sector, size);
-
-	/*
-	 * let the block layer decide on the fastest method of
-	 * implementing the zeroing.
-	 */
-	return sb_issue_zeroout(mp->m_super, block, count_fsb, GFP_NOFS);
 
+	return blkdev_issue_zeroout(xfs_find_bdev_for_inode(VFS_I(ip)),
+		block << (mp->m_super->s_blocksize_bits - 9),
+		count_fsb << (mp->m_super->s_blocksize_bits - 9),
+		GFP_NOFS, true);
 }
 
 /*
diff --git a/include/linux/dax.h b/include/linux/dax.h
index ef94fa7..426841a 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -11,7 +11,6 @@
 
 ssize_t dax_do_io(struct kiocb *, struct inode *, struct iov_iter *, loff_t,
 		  get_block_t, dio_iodone_t, int flags);
-int dax_clear_sectors(struct block_device *bdev, sector_t _sector, long _size);
 int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
 int dax_truncate_page(struct inode *, loff_t from, get_block_t);
 int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
-- 
2.5.5

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