On Thu, Jul 27, 2017 at 03:12:43PM +0200, Jan Kara wrote: > Add a flag to iomap interface informing the caller that inode needs > fdstasync(2) for returned extent to become persistent and use it in DAX > fault code so that we map such extents only read only. We propagate the > information that the page table entry has been inserted write-protected > from dax_iomap_fault() with a new VM_FAULT_RO flag. Filesystem fault > handler is then responsible for calling fdatasync(2) and updating page > tables to map pfns read-write. dax_iomap_fault() also takes care of > updating vmf->orig_pte to match the PTE that was inserted so that we can > safely recheck that PTE did not change while write-enabling it. > > Signed-off-by: Jan Kara <jack@xxxxxxx> <> > @@ -1385,9 +1409,13 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, bool sync, > if (iomap.offset + iomap.length < pos + PMD_SIZE) > goto finish_iomap; > > + force_ro = (vmf->flags & FAULT_FLAG_WRITE) && sync && > + (iomap.flags & IOMAP_F_NEEDDSYNC); I already mentioned this in my response to your cover letter, but I think that we can just lean really heavily on IOMAP_F_NEEDDSYNC and have that let us know that we are doing sync faults and that the fault is a write. That simplifies a few things in this patch, with the above just becoming: force_ro = (iomap.flags & IOMAP_F_NEEDDSYNC); > diff --git a/include/linux/mm.h b/include/linux/mm.h > index fa036093e76c..5085647d9f2f 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1142,6 +1142,8 @@ static inline void clear_page_pfmemalloc(struct page *page) > #define VM_FAULT_RETRY 0x0400 /* ->fault blocked, must retry */ > #define VM_FAULT_FALLBACK 0x0800 /* huge page fault failed, fall back to small */ > #define VM_FAULT_DONE_COW 0x1000 /* ->fault has fully handled COW */ > +#define VM_FAULT_RO 0x2000 /* Write fault was handled just by > + * inserting RO page table entry for DAX */ I wonder if we should name this flag something a little stronger and more specific to its usage with respect to DAX and sync faults? Maybe "VM_FAULT_NEEDDSYNC" for consistency with the iomap flag?
