From 8346c416d17bf5b4ea1508662959bb62e73fd6a5 Mon Sep 17 00:00:00 2001 From: Ross Zwisler Date: Thu, 1 Oct 2015 15:36:59 -0700 Subject: [PATCH] dax: fix NULL pointer in __dax_pmd_fault() 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', 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 Reported-by: Dan Williams Reviewed-by: Dan Williams Cc: Alexander Viro Cc: Matthew Wilcox Cc: "Kirill A. Shutemov" Cc: Dave Chinner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/dax.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/fs/dax.c b/fs/dax.c index 7ae6df7ea1d2..bcfb14bfc1e4 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) { -- 2.20.1