On Wed, Oct 14, 2015 at 04:25:50PM +1100, Dave Chinner wrote: > On Tue, Oct 13, 2015 at 04:25:36PM -0600, Ross Zwisler wrote: > > Update dax_pfn_mkwrite() so that it validates i_size before returning. > > This is necessary to ensure that the page fault has not raced with truncate > > and is now pointing to a region beyond the end of the current file. > > > > This change is based on a similar outstanding patch for XFS from Dave > > Chinner entitled "xfs: add ->pfn_mkwrite support for DAX". > > > > Signed-off-by: Ross Zwisler <[email protected]> > > Cc: Dave Chinner <[email protected]> > > --- > > fs/dax.c | 13 +++++++++++-- > > 1 file changed, 11 insertions(+), 2 deletions(-) > > > > diff --git a/fs/dax.c b/fs/dax.c > > index 131fd35a..82be6e4 100644 > > --- a/fs/dax.c > > +++ b/fs/dax.c > > @@ -693,12 +693,21 @@ EXPORT_SYMBOL_GPL(dax_pmd_fault); > > */ > > int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf) > > { > > - struct super_block *sb = file_inode(vma->vm_file)->i_sb; > > + struct inode *inode = file_inode(vma->vm_file); > > + struct super_block *sb = inode->i_sb; > > + int ret = VM_FAULT_NOPAGE; > > + loff_t size; > > > > sb_start_pagefault(sb); > > file_update_time(vma->vm_file); > > + > > + /* check that the faulting page hasn't raced with truncate */ > > + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT; > > + if (vmf->pgoff >= size) > > + ret = VM_FAULT_SIGBUS; > > + > > sb_end_pagefault(sb); > > - return VM_FAULT_NOPAGE; > > + return ret; > > This is still racy, as the read of the inode size is not serialised > against or ordered by any locks held by truncate. The check in XFS > is serialised against truncate by the XFS_MMAPLOCK and the generic > DAX code does not have such a mechanism to rely on. Hence I'd > suggest that the correct thing to do here is remove > dax_pfn_mkwrite() and force filesystems to implement their own > truncate-safe variants of ->pfn_mkwrite.
Agreed, let's just drop this patch and remove dax_pfn_mkwrite(). The last user of this function was ext4, and that usage goes away with Jan's latest patch set. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
