mm: describe mmap_sem rules for __lock_page_or_retry() and callers
Add a comment describing the circumstances in which
__lock_page_or_retry() will or will not release the mmap_sem when
returning 0.
Add comments to lock_page_or_retry()'s callers (filemap_fault(),
do_swap_page()) noting the impact on VM_FAULT_RETRY returns.
Add comments on up the call tree, particularly replacing the false "We
return with mmap_sem still held" comments.
Signed-off-by: Paul Cassella <cassella@cray.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 1dbade8..a241946 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1218,7 +1218,8 @@
/*
* If for any reason at all we couldn't handle the fault,
* make sure we exit gracefully rather than endlessly redo
- * the fault:
+ * the fault. Since we never set FAULT_FLAG_RETRY_NOWAIT, if
+ * we get VM_FAULT_RETRY back, the mmap_sem has been unlocked.
*/
fault = handle_mm_fault(mm, vma, address, flags);