The patch titled
Subject: dax: fix conversion of holes to PMDs
has been added to the -mm tree. Its filename is
dax-fix-conversion-of-holes-to-pmds.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/dax-fix-conversion-of-holes-to-pmds.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/dax-fix-conversion-of-holes-to-pmds.patch
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------------------------------------------------------
From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Subject: dax: fix conversion of holes to PMDs
When we get a DAX PMD fault for a write it is possible that there could be
some number of 4k zero pages already present for the same range that were
inserted to service reads from a hole. These 4k zero pages need to be
unmapped from the VMAs and removed from the struct address_space radix
tree before the real DAX PMD entry can be inserted.
For PTE faults this same use case also exists and is handled by a
combination of unmap_mapping_range() to unmap the VMAs and
delete_from_page_cache() to remove the page from the address_space radix
tree.
For PMD faults we do have a call to unmap_mapping_range() (protected by a
buffer_new() check), but nothing clears out the radix tree entry. The
buffer_new() check is also incorrect as the current ext4 and XFS
filesystem code will never return a buffer_head with BH_New set, even when
allocating new blocks over a hole. Instead the filesystem will zero the
blocks manually and return a buffer_head with only BH_Mapped set.
Fix this situation by removing the buffer_new() check and adding a call to
truncate_inode_pages_range() to clear out the radix tree entries before we
insert the DAX PMD.
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Tested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff -puN fs/dax.c~dax-fix-conversion-of-holes-to-pmds fs/dax.c
--- a/fs/dax.c~dax-fix-conversion-of-holes-to-pmds
+++ a/fs/dax.c
@@ -594,6 +594,7 @@ int __dax_pmd_fault(struct vm_area_struc
bool write = flags & FAULT_FLAG_WRITE;
struct block_device *bdev;
pgoff_t size, pgoff;
+ loff_t lstart, lend;
sector_t block;
int result = 0;
@@ -647,15 +648,13 @@ int __dax_pmd_fault(struct vm_area_struc
goto fallback;
}
- /*
- * If we allocated new storage, make sure no process has any
- * zero pages covering this hole
- */
- if (buffer_new(&bh)) {
- i_mmap_unlock_read(mapping);
- unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
- i_mmap_lock_read(mapping);
- }
+ /* make sure no process has any zero pages covering this hole */
+ lstart = pgoff << PAGE_SHIFT;
+ lend = lstart + PMD_SIZE - 1; /* inclusive */
+ i_mmap_unlock_read(mapping);
+ unmap_mapping_range(mapping, lstart, PMD_SIZE, 0);
+ truncate_inode_pages_range(mapping, lstart, lend);
+ i_mmap_lock_read(mapping);
/*
* If a truncate happened while we were allocating blocks, we may
@@ -669,7 +668,8 @@ int __dax_pmd_fault(struct vm_area_struc
goto out;
}
if ((pgoff | PG_PMD_COLOUR) >= size) {
- dax_pmd_dbg(&bh, address, "pgoff unaligned");
+ dax_pmd_dbg(&bh, address,
+ "offset + huge page size > file size");
goto fallback;
}
_
Patches currently in -mm which might be from ross.zwisler@xxxxxxxxxxxxxxx are
mm-dax-fix-livelock-allow-dax-pmd-mappings-to-become-writeable.patch
dax-fix-null-pointer-dereference-in-__dax_dbg.patch
dax-fix-conversion-of-holes-to-pmds.patch
pmem-add-wb_cache_pmem-to-the-pmem-api.patch
pmem-add-wb_cache_pmem-to-the-pmem-api-v6.patch
dax-support-dirty-dax-entries-in-radix-tree.patch
dax-support-dirty-dax-entries-in-radix-tree-v6.patch
mm-add-find_get_entries_tag.patch
dax-add-support-for-fsync-sync.patch
dax-add-support-for-fsync-sync-v6.patch
dax-add-support-for-fsync-msync-v7.patch
ext2-call-dax_pfn_mkwrite-for-dax-fsync-msync.patch
ext4-call-dax_pfn_mkwrite-for-dax-fsync-msync.patch
xfs-call-dax_pfn_mkwrite-for-dax-fsync-msync.patch
--
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