The patch titled Subject: dax: fix PMD data corruption when fault races with write has been removed from the -mm tree. Its filename was dax-fix-pmd-data-corruption-when-fault-races-with-write.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Subject: dax: fix PMD data corruption when fault races with write This is based on a patch from Jan Kara that fixed the equivalent race in the DAX PTE fault path. Currently DAX PMD read fault can race with write(2) in the following way: CPU1 - write(2) CPU2 - read fault dax_iomap_pmd_fault() ->iomap_begin() - sees hole dax_iomap_rw() iomap_apply() ->iomap_begin - allocates blocks dax_iomap_actor() invalidate_inode_pages2_range() - there's nothing to invalidate grab_mapping_entry() - we add huge zero page to the radix tree and map it to page tables The result is that hole page is mapped into page tables (and thus zeros are seen in mmap) while file has data written in that place. Fix the problem by locking exception entry before mapping blocks for the fault. That way we are sure invalidate_inode_pages2_range() call for racing write will either block on entry lock waiting for the fault to finish (and unmap stale page tables after that) or read fault will see already allocated blocks by write(2). Fixes: 9f141d6ef6258 ("dax: Call ->iomap_begin without entry lock during dax fault") Link: http://lkml.kernel.org/r/20170510172700.18991-1-ross.zwisler@xxxxxxxxxxxxxxx Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Reviewed-by: Jan Kara <jack@xxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/dax.c | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-) diff -puN fs/dax.c~dax-fix-pmd-data-corruption-when-fault-races-with-write fs/dax.c --- a/fs/dax.c~dax-fix-pmd-data-corruption-when-fault-races-with-write +++ a/fs/dax.c @@ -1388,6 +1388,16 @@ static int dax_iomap_pmd_fault(struct vm goto fallback; /* + * grab_mapping_entry() will make sure we get a 2M empty entry, a DAX + * PMD or a HZP entry. If it can't (because a 4k page is already in + * the tree, for instance), it will return -EEXIST and we just fall + * back to 4k entries. + */ + entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD); + if (IS_ERR(entry)) + goto fallback; + + /* * Note that we don't use iomap_apply here. We aren't doing I/O, only * setting up a mapping, so really we're using iomap_begin() as a way * to look up our filesystem block. @@ -1395,21 +1405,11 @@ static int dax_iomap_pmd_fault(struct vm pos = (loff_t)pgoff << PAGE_SHIFT; error = ops->iomap_begin(inode, pos, PMD_SIZE, iomap_flags, &iomap); if (error) - goto fallback; + goto unlock_entry; if (iomap.offset + iomap.length < pos + PMD_SIZE) goto finish_iomap; - /* - * grab_mapping_entry() will make sure we get a 2M empty entry, a DAX - * PMD or a HZP entry. If it can't (because a 4k page is already in - * the tree, for instance), it will return -EEXIST and we just fall - * back to 4k entries. - */ - entry = grab_mapping_entry(mapping, pgoff, RADIX_DAX_PMD); - if (IS_ERR(entry)) - goto finish_iomap; - switch (iomap.type) { case IOMAP_MAPPED: result = dax_pmd_insert_mapping(vmf, &iomap, pos, &entry); @@ -1417,7 +1417,7 @@ static int dax_iomap_pmd_fault(struct vm case IOMAP_UNWRITTEN: case IOMAP_HOLE: if (WARN_ON_ONCE(write)) - goto unlock_entry; + break; result = dax_pmd_load_hole(vmf, &iomap, &entry); break; default: @@ -1425,8 +1425,6 @@ static int dax_iomap_pmd_fault(struct vm break; } - unlock_entry: - put_locked_mapping_entry(mapping, pgoff, entry); finish_iomap: if (ops->iomap_end) { int copied = PMD_SIZE; @@ -1442,6 +1440,8 @@ static int dax_iomap_pmd_fault(struct vm ops->iomap_end(inode, pos, PMD_SIZE, copied, iomap_flags, &iomap); } + unlock_entry: + put_locked_mapping_entry(mapping, pgoff, entry); fallback: if (result == VM_FAULT_FALLBACK) { split_huge_pmd(vma, vmf->pmd, vmf->address); _ Patches currently in -mm which might be from ross.zwisler@xxxxxxxxxxxxxxx are