From de14b9cb5e02b5daaea139590393af5ccccc4229 Mon Sep 17 00:00:00 2001 From: Ross Zwisler Date: Fri, 22 Jan 2016 15:10:34 -0800 Subject: [PATCH] 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 Reported-by: Dan Williams Tested-by: Dan Williams Reviewed-by: Jan Kara Cc: "H. Peter Anvin" Cc: "J. Bruce Fields" Cc: "Theodore Ts'o" Cc: Alexander Viro Cc: Andreas Dilger Cc: Dave Chinner Cc: Ingo Molnar Cc: Jeff Layton Cc: Matthew Wilcox Cc: Thomas Gleixner Cc: Matthew Wilcox Cc: Dave Hansen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/dax.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 513bba5f1e02..5b84a46201c2 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -589,6 +589,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, bool write = flags & FAULT_FLAG_WRITE; struct block_device *bdev; pgoff_t size, pgoff; + loff_t lstart, lend; sector_t block; int result = 0; @@ -643,15 +644,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, 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 @@ -665,7 +664,8 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, 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; } -- 2.30.2