On Thu 21-12-17 09:12:52, Dan Williams wrote:

On Thu, Dec 21, 2017 at 8:30 AM, Jan Kara [off-list ref] wrote:

quoted

Ext4 needs to pass through error from its iomap handler to the page
fault handler so that it can properly detect ENOSPC and force
transaction commit and retry the fault (and block allocation). Add
argument to dax_iomap_fault() for passing such error.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/dax.c            | 9 ++++++---
 fs/ext2/file.c      | 2 +-
 fs/ext4/file.c      | 2 +-
 fs/xfs/xfs_file.c   | 2 +-
 include/linux/dax.h | 2 +-
 5 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 95981591977a..f3afa1d6156c 100644
--- a/fs/dax.c
+++ b/fs/dax.c

@@ -1096,7 +1096,7 @@ static bool dax_fault_is_synchronous(unsigned long flags,
 }

 static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
-                              const struct iomap_ops *ops)
+                              int *iomap_errp, const struct iomap_ops *ops)
 {
        struct vm_area_struct *vma = vmf->vma;
        struct address_space *mapping = vma->vm_file->f_mapping;

@@ -1149,6 +1149,8 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
         * that we never have to deal with more than a single extent here.
         */
        error = ops->iomap_begin(inode, pos, PAGE_SIZE, flags, &iomap);
+       if (iomap_errp)
+               *iomap_errp = error;

Since we already have 'struct iomap' tracking the state of the iomap
should we track the error status there as well?  I.e. move the on
stack allocation of struct iomap to the per-fs dax fault handlers.

I don't think that's really adequate. Firstly because at least part of
struct iomap needs to be initialized inside dax_iomap_fault() and secondly
because by the time dax_iomap_fault() returns, mapping information in struct
iomap may be invalid (as we unlocked radix tree entry). So I think it is
really better to pass back only the error code and keep struct iomap
internal to dax_iomap_fault().

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR