dax: Use radix tree entry lock to protect cow faults
When doing cow faults, we cannot directly fill in PTE as we do for other
faults as we rely on generic code to do proper accounting of the cowed page.
We also have no page to lock to protect against races with truncate as
other faults have and we need the protection to extend until the moment
generic code inserts cowed page into PTE thus at that point we have no
protection of fs-specific i_mmap_sem. So far we relied on using
i_mmap_lock for the protection however that is completely special to cow
faults. To make fault locking more uniform use DAX entry lock instead.
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a55e5be..0ef9dc72 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -299,6 +299,12 @@
* is set (which is also implied by
* VM_FAULT_ERROR).
*/
+ void *entry; /* ->fault handler can alternatively
+ * return locked DAX entry. In that
+ * case handler should return
+ * VM_FAULT_DAX_LOCKED and fill in
+ * entry here.
+ */
/* for ->map_pages() only */
pgoff_t max_pgoff; /* map pages for offset from pgoff till
* max_pgoff inclusive */
@@ -1084,6 +1090,7 @@
#define VM_FAULT_LOCKED 0x0200 /* ->fault locked the returned 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_DAX_LOCKED 0x1000 /* ->fault has locked DAX entry */
#define VM_FAULT_HWPOISON_LARGE_MASK 0xf000 /* encodes hpage index for large hwpoison */