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Message-Id: <1452230879-18117-3-git-send-email-ross.zwisler@linux.intel.com>
Date: Thu, 7 Jan 2016 22:27:52 -0700
From: Ross Zwisler <ross.zwisler@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
"J. Bruce Fields" <bfields@...ldses.org>,
"Theodore Ts'o" <tytso@....edu>,
Alexander Viro <viro@...iv.linux.org.uk>,
Andreas Dilger <adilger.kernel@...ger.ca>,
Andrew Morton <akpm@...ux-foundation.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Chinner <david@...morbit.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>, Jan Kara <jack@...e.com>,
Jeff Layton <jlayton@...chiereds.net>,
Matthew Wilcox <matthew.r.wilcox@...el.com>,
Matthew Wilcox <willy@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-nvdimm@...ts.01.org, x86@...nel.org,
xfs@....sgi.com
Subject: [PATCH v8 2/9] 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@...ux.intel.com>
Reported-by: Dan Williams <dan.j.williams@...el.com>
Tested-by: Dan Williams <dan.j.williams@...el.com>
---
fs/dax.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 513bba5..5b84a46 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;
}
--
2.5.0
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