mm: add comment on swap_duplicate's error code

swap_duplicate()'s loop appears to miss out on returning the error code from __swap_duplicate(), except when that's -ENOMEM. In fact this is intentional: prior to -ENOMEM for swap_count_continuation, swap_duplicate() was void (and the case only occurs when copy_one_pte() hits a corrupt pte). But that's surprising behaviour, which certainly deserves a comment. Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Huang Shijie <shijie8@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm: add comment on swap_duplicate's error code
swap_duplicate()'s loop appears to miss out on returning the error code from __swap_duplicate(), except when that's -ENOMEM. In fact this is intentional: prior to -ENOMEM for swap_count_continuation, swap_duplicate() was void (and the case only occurs when copy_one_pte() hits a corrupt pte). But that's surprising behaviour, which certainly deserves a comment. Signed-off-by: Hugh Dickins <hughd@google.com> Reported-by: Huang Shijie <shijie8@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Hugh Dickins · Linus Torvalds
1 parent c08c6e1f54
Showing 1 changed file with 5 additions and 1 deletions Side-by-side Diff
mm/swapfile.c
@@ -2161,7 +2161,11 @@
 }
  
 /*
- * increase reference count of swap entry by 1.
+ * Increase reference count of swap entry by 1.
+ * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
+ * but could not be atomically allocated.  Returns 0, just as if it succeeded,
+ * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
+ * might occur if a page table entry has got corrupted.
  */
 int swap_duplicate(swp_entry_t entry)
 {
...	...	@@ -2161,7 +2161,11 @@
2161	2161	}
2162	2162
2163	2163	/*
2164		- * increase reference count of swap entry by 1.
	2164	+ * Increase reference count of swap entry by 1.
	2165	+ * Returns 0 for success, or -ENOMEM if a swap_count_continuation is required
	2166	+ * but could not be atomically allocated. Returns 0, just as if it succeeded,
	2167	+ * if __swap_duplicate() fails for another reason (-EINVAL or -ENOENT), which
	2168	+ * might occur if a page table entry has got corrupted.
2165	2169	*/
2166	2170	int swap_duplicate(swp_entry_t entry)
2167	2171	{