From ef13552601b20b3bda6f32d907777d28130282f0 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Fri, 12 May 2017 15:46:57 -0700 Subject: [PATCH] dax: fix data corruption when fault races with write Currently DAX read fault can race with write(2) in the following way: CPU1 - write(2) CPU2 - read fault dax_iomap_pte_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 zero page in 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: 724fa8d602970d4e05b4c04731e1b5812eecc65c Link: http://lkml.kernel.org/r/20170510085419.27601-5-jack@suse.cz Signed-off-by: Jan Kara Reviewed-by: Ross Zwisler Cc: Dan Williams Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/dax.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 123d9903c77d8..32f020c9cedf0 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1148,6 +1148,12 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, if ((vmf->flags & FAULT_FLAG_WRITE) && !vmf->cow_page) flags |= IOMAP_WRITE; + entry = grab_mapping_entry(mapping, vmf->pgoff, 0); + if (IS_ERR(entry)) { + vmf_ret = dax_fault_return(PTR_ERR(entry)); + goto out; + } + /* * Note that we don't bother to use iomap_apply here: DAX required * the file system block size to be equal the page size, which means @@ -1156,17 +1162,11 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap); if (error) { vmf_ret = dax_fault_return(error); - goto out; + goto unlock_entry; } if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) { - vmf_ret = dax_fault_return(-EIO); /* fs corruption? */ - goto finish_iomap; - } - - entry = grab_mapping_entry(mapping, vmf->pgoff, 0); - if (IS_ERR(entry)) { - vmf_ret = dax_fault_return(PTR_ERR(entry)); - goto finish_iomap; + error = -EIO; /* fs corruption? */ + goto error_finish_iomap; } sector = dax_iomap_sector(&iomap, pos); @@ -1188,13 +1188,13 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, } if (error) - goto error_unlock_entry; + goto error_finish_iomap; __SetPageUptodate(vmf->cow_page); vmf_ret = finish_fault(vmf); if (!vmf_ret) vmf_ret = VM_FAULT_DONE_COW; - goto unlock_entry; + goto finish_iomap; } switch (iomap.type) { @@ -1214,7 +1214,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, case IOMAP_HOLE: if (!(vmf->flags & FAULT_FLAG_WRITE)) { vmf_ret = dax_load_hole(mapping, &entry, vmf); - goto unlock_entry; + goto finish_iomap; } /*FALLTHRU*/ default: @@ -1223,10 +1223,8 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, break; } - error_unlock_entry: + error_finish_iomap: vmf_ret = dax_fault_return(error) | major; - unlock_entry: - put_locked_mapping_entry(mapping, vmf->pgoff, entry); finish_iomap: if (ops->iomap_end) { int copied = PAGE_SIZE; @@ -1241,7 +1239,9 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, */ ops->iomap_end(inode, pos, PAGE_SIZE, copied, flags, &iomap); } -out: + unlock_entry: + put_locked_mapping_entry(mapping, vmf->pgoff, entry); + out: trace_dax_pte_fault_done(inode, vmf, vmf_ret); return vmf_ret; } -- 2.39.5