On Thu 27-07-17 16:22:30, Ross Zwisler wrote:

On Thu, Jul 27, 2017 at 03:12:42PM +0200, Jan Kara wrote:

quoted

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@suse.cz>
---
 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

Yeah, this was the intention (as my eventually I'd like to make
dax_insert_mapping() and dax_pmd_insert_mapping() one function - they are
already currently very similar). I'll fix the missed cases.

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