On Thu, Jul 27, 2017 at 03:12:42PM +0200, Jan Kara wrote:
> Currently dax_insert_mapping() returns normal error code which is later
> converted to VM_FAULT_ state. Since we will need to do more state
> modifications specific to dax_insert_mapping() it does not make sense to
> push them up to the caller of dax_insert_mapping(). Instead make
> dax_insert_mapping() return VM_FAULT_ state the same way as
> dax_pmd_insert_mapping() does that.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> fs/dax.c | 45 +++++++++++++++++++++++++--------------------
> 1 file changed, 25 insertions(+), 20 deletions(-)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 0673efd72f53..9658975b926a 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -814,6 +814,15 @@ int dax_writeback_mapping_range(struct address_space *mapping,
> }
> EXPORT_SYMBOL_GPL(dax_writeback_mapping_range);
>
> +static int dax_fault_return(int error)
> +{
> + if (error == 0)
> + return VM_FAULT_NOPAGE;
> + if (error == -ENOMEM)
> + return VM_FAULT_OOM;
> + return VM_FAULT_SIGBUS;
> +}
> +
> static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
> {
> return iomap->blkno + (((pos & PAGE_MASK) - iomap->offset) >> 9);
> @@ -828,7 +837,7 @@ static int dax_insert_mapping(struct vm_fault *vmf, struct iomap *iomap,
> unsigned long vaddr = vmf->address;
> void *ret, *kaddr;
> pgoff_t pgoff;
> - int id, rc;
> + int id, rc, vmf_ret;
> pfn_t pfn;
>
> rc = bdev_dax_pgoff(iomap->bdev, sector, PAGE_SIZE, &pgoff);
> @@ -850,9 +859,18 @@ static int dax_insert_mapping(struct vm_fault *vmf, struct iomap *iomap,
>
> trace_dax_insert_mapping(mapping->host, vmf, ret);
> if (vmf->flags & FAULT_FLAG_WRITE)
> - return vm_insert_mixed_mkwrite(vma, vaddr, pfn);
> + rc = vm_insert_mixed_mkwrite(vma, vaddr, pfn);
> else
> - return vm_insert_mixed(vma, vaddr, pfn);
> + rc = vm_insert_mixed(vma, vaddr, pfn);
> +
> + /* -EBUSY is fine, somebody else faulted on the same PTE */
> + if (rc == -EBUSY)
> + rc = 0;
> +
> + vmf_ret = dax_fault_return(rc);
Prior to this point where we convert our 'rc' (which is a normal error code
like 0, -ENOMEM, etc) to a 'vmf_ret' (which is a VM return code like
VM_FAULT_NOPAGE, VM_FAULT_SIGBUS, etc), there are several paths in
dax_insert_mapping() where we could still return a normal error code. I think
this will confuse the fault handler because this code will get returned all
the way up to do_fault() which expects to get a VM return code.
So, I think we either need to:
a) Make sure all return paths through dax_insert_mapping() end up going
through dax_fault_return(), as we do in the PMD case, or
b) Keep allowing this function to return normal error codes, and just teach
dax_fault_return() to look for IOMAP_F_NEEDSYNC flag so it knows when to set
VM_FAULT_RO.
