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@linux.intel.com> Reported-by: Dan Williams <dan.j.williams@intel.com> Tested-by: Dan Williams <dan.j.williams@intel.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: "J. Bruce Fields" <bfields@fieldses.org> Cc: "Theodore Ts'o" <tytso@mit.edu> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Andreas Dilger <adilger.kernel@dilger.ca> Cc: Dave Chinner <david@fromorbit.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jeff Layton <jlayton@poochiereds.net> Cc: Matthew Wilcox <willy@linux.intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Matthew Wilcox <matthew.r.wilcox@intel.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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parent
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20
fs/dax.c
20
fs/dax.c
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@ -589,6 +589,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
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bool write = flags & FAULT_FLAG_WRITE;
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struct block_device *bdev;
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pgoff_t size, pgoff;
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loff_t lstart, lend;
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sector_t block;
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int result = 0;
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@ -643,15 +644,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
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goto fallback;
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}
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/*
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* If we allocated new storage, make sure no process has any
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* zero pages covering this hole
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*/
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if (buffer_new(&bh)) {
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i_mmap_unlock_read(mapping);
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unmap_mapping_range(mapping, pgoff << PAGE_SHIFT, PMD_SIZE, 0);
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i_mmap_lock_read(mapping);
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}
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/* make sure no process has any zero pages covering this hole */
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lstart = pgoff << PAGE_SHIFT;
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lend = lstart + PMD_SIZE - 1; /* inclusive */
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i_mmap_unlock_read(mapping);
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unmap_mapping_range(mapping, lstart, PMD_SIZE, 0);
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truncate_inode_pages_range(mapping, lstart, lend);
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i_mmap_lock_read(mapping);
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/*
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* If a truncate happened while we were allocating blocks, we may
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@ -665,7 +664,8 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
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goto out;
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}
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if ((pgoff | PG_PMD_COLOUR) >= size) {
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dax_pmd_dbg(&bh, address, "pgoff unaligned");
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dax_pmd_dbg(&bh, address,
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"offset + huge page size > file size");
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goto fallback;
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}
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