On Thu, May 18, 2017 at 09:26:04AM +0200, gregkh@xxxxxxxxxxxxxxxxxxx wrote: > > The patch below does not apply to the 4.11-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <stable@xxxxxxxxxxxxxxx>. > > thanks, > > greg k-h The following patch from Jan was sent in v3 of his series before he had merged with my tracepoint changes, and applies cleanly to v4.11.1. This is for the following upstream commit: commit 13e451fdc1af ("dax: fix data corruption when fault races with write") --- >8 --- >From d23bb209e613befbf568c54298bb3add847653a0 Mon Sep 17 00:00:00 2001 From: Jan Kara <jack@xxxxxxx> Date: Tue, 9 May 2017 14:18:37 +0200 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: 9f141d6ef6258a3a37a045842d9ba7e68f368956 CC: stable@xxxxxxxxxxxxxxx Reviewed-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> Signed-off-by: Jan Kara <jack@xxxxxxx> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> --- fs/dax.c | 32 ++++++++++++++++---------------- 1 file changed, 16 insertions(+), 16 deletions(-) diff --git a/fs/dax.c b/fs/dax.c index 85abd74..d1d2cd9 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -1153,23 +1153,23 @@ 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)) + return dax_fault_return(PTR_ERR(entry)); + /* * 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 * that we never have to deal with more than a single extent here. */ error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap); - if (error) - return dax_fault_return(error); - if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) { - vmf_ret = dax_fault_return(-EIO); /* fs corruption? */ - goto finish_iomap; + if (error) { + vmf_ret = dax_fault_return(error); + goto unlock_entry; } - - entry = grab_mapping_entry(mapping, vmf->pgoff, 0); - if (IS_ERR(entry)) { - vmf_ret = dax_fault_return(PTR_ERR(entry)); - goto finish_iomap; + if (WARN_ON_ONCE(iomap.offset + iomap.length < pos + PAGE_SIZE)) { + error = -EIO; /* fs corruption? */ + goto error_finish_iomap; } sector = dax_iomap_sector(&iomap, pos); @@ -1191,13 +1191,13 @@ 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) { @@ -1217,7 +1217,7 @@ 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: @@ -1226,10 +1226,8 @@ 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; @@ -1244,6 +1242,8 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, */ ops->iomap_end(inode, pos, PAGE_SIZE, copied, flags, &iomap); } + unlock_entry: + put_locked_mapping_entry(mapping, vmf->pgoff, entry); return vmf_ret; } -- 2.9.4