The following commit:
commit 46c043ede471 ("mm: take i_mmap_lock in unmap_mapping_range() for
DAX")
moved some code in __dax_pmd_fault() that was responsible for zeroing
newly allocated PMD pages. The new location didn't properly set up
'kaddr', though, so when run this code resulted in a NULL pointer BUG.
Fix this by getting the correct 'kaddr' via bdev_direct_access().
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
fs/dax.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/fs/dax.c b/fs/dax.c
index 7ae6df7..bcfb14b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -569,8 +569,20 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
goto fallback;
+ sector = bh.b_blocknr << (blkbits - 9);
+
if (buffer_unwritten(&bh) || buffer_new(&bh)) {
int i;
+
+ length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
+ bh.b_size);
+ if (length < 0) {
+ result = VM_FAULT_SIGBUS;
+ goto out;
+ }
+ if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
+ goto fallback;
+
for (i = 0; i < PTRS_PER_PMD; i++)
clear_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE);
wmb_pmem();
@@ -623,7 +635,6 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
result = VM_FAULT_NOPAGE;
spin_unlock(ptl);
} else {
- sector = bh.b_blocknr << (blkbits - 9);
length = bdev_direct_access(bh.b_bdev, sector, &kaddr, &pfn,
bh.b_size);
if (length < 0) {
--
2.1.0
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