mm/page_ext: enable early_page_ext when CONFIG_MEM_ALLOC_PROFILING_DEBUG=y

For all page allocations to be tagged, page_ext has to be initialized
before the first page allocation.  Early tasks allocate their stacks using
page allocator before alloc_node_page_ext() initializes page_ext area,
unless early_page_ext is enabled.  Therefore these allocations will
generate a warning when CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled. 
Enable early_page_ext whenever CONFIG_MEM_ALLOC_PROFILING_DEBUG=y to
ensure page_ext initialization prior to any page allocation.  This will
have all the negative effects associated with early_page_ext, such as
possible longer boot time, therefore we enable it only when debugging with
CONFIG_MEM_ALLOC_PROFILING_DEBUG enabled and not universally for
CONFIG_MEM_ALLOC_PROFILING.

Link: https://lkml.kernel.org/r/20240321163705.3067592-22-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Tested-by: Kees Cook <keescook@chromium.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alex Gaynor <alex.gaynor@gmail.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Andreas Hindborg <a.hindborg@samsung.com>
Cc: Benno Lossin <benno.lossin@proton.me>
Cc: "Björn Roy Baron" <bjorn3_gh@protonmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Gary Guo <gary@garyguo.net>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Miguel Ojeda <ojeda@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/page_ext.c

@@ -95,7 +95,16 @@ unsigned long page_ext_size;
 
 static unsigned long total_usage;
 
+#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
+/*
+ * To ensure correct allocation tagging for pages, page_ext should be available
+ * before the first page allocation. Otherwise early task stacks will be
+ * allocated before page_ext initialization and missing tags will be flagged.
+ */
+bool early_page_ext __meminitdata = true;
+#else
 bool early_page_ext __meminitdata;
+#endif
 static int __init setup_early_page_ext(char *str)
 {
 	early_page_ext = true;