On Tue, Mar 05, 2024 at 08:47:40PM -0800, Linus Torvalds wrote:
> On Tue, 5 Mar 2024 at 20:37, Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:
> >
> > +static struct page *dump_page_copy(struct page *src, struct page *dst)
> > +{
> > + return NULL;
> > +}
>
> No, it needs to be "return src;" not NULL.
>
> That
>
> #define dump_page_copy(src, dst) ((dst), (src))
>
> was supposed to be a "use 'dst', return 'src'" macro, and is correct
> as that. The problem - as you noticed - is that it causes that "left
> side of comma expression has no effect" warning.
>
> (Technically it *does* have an effect - exactly the "argument is used"
> one - but the compiler warning does make sense).
>
> Actually, the simplest thing to do is probably just
>
> #define dump_page_free(x) ((void)(x))
> #define dump_page_copy(src, dst) (src)
>
> where the "use" of the 'dump_page' argument is that dump_page_free()
> void cast, and dump_page_copy() simply doesn't need to use it at all.
>
> Christian?
I would just do it like Stephen did (but returning src ofc) because it's
symmetric to the #ifdef copy_mc_to_kernel definition of dump_page_copy()
and seems easier to read to me.
But I honestly don't care too much. So I'd pick Stephen's change and if
you prefer to do it differently just change it when I send you the pr.
+/*
+ * If we might get machine checks from kernel accesses during the
+ * core dump, let's get those errors early rather than during the
+ * IO. This is not performance-critical enough to warrant having
+ * all the machine check logic in the iovec paths.
+ */
+#ifdef copy_mc_to_kernel
+
+#define dump_page_alloc() alloc_page(GFP_KERNEL)
+#define dump_page_free(x) __free_page(x)
+static struct page *dump_page_copy(struct page *src, struct page *dst)
+{
+ void *buf = kmap_local_page(src);
+ size_t left = copy_mc_to_kernel(page_address(dst), buf, PAGE_SIZE);
+ kunmap_local(buf);
+ return left ? NULL : dst;
+}
+
+#else
+
+/* We just want to return non-NULL; it's never used. */
+#define dump_page_alloc() ERR_PTR(-EINVAL)
+#define dump_page_free(x) ((void)(x))
+static inline struct page *dump_page_copy(struct page *src, struct page *dst)
+{
+ return src;
+}
+#endif
