Currently the handling of huge pages for DAX is racy. For example the
following can happen:
CPU0 (THP write fault) CPU1 (normal read fault)
__dax_pmd_fault() __dax_fault()
get_block(inode, block, &bh, 0) -> not mapped
get_block(inode, block, &bh, 0)
-> not mapped
if (!buffer_mapped(&bh) && write)
get_block(inode, block, &bh, 1) -> allocates blocks
truncate_pagecache_range(inode, lstart, lend);
dax_load_hole();
This results in data corruption since process on CPU1 won't see changes
into the file done by CPU0.
The race can happen even if two normal faults race however with THP the
situation is even worse because the two faults don't operate on the same
entries in the radix tree and we want to use these entries for
serialization. So disable THP support in DAX code for now.
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/dax.c | 2 +-
include/linux/dax.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 3951237ff248..7148fcdb2c92 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -715,7 +715,7 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
}
EXPORT_SYMBOL_GPL(dax_fault);
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#if 0
/*
* The 'colour' (ie low bits) within a PMD of a page offset. This comes up
* more often than one might expect in the below function.
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 4b63923e1f8d..fd28d824254b 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -29,7 +29,7 @@ static inline struct page *read_dax_sector(struct block_device *bdev,
}
#endif
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#if 0
int dax_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *,
unsigned int flags, get_block_t);
int __dax_pmd_fault(struct vm_area_struct *, unsigned long addr, pmd_t *,
--
2.6.2
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