[PATCH v3] mm: memblock: show all region flags in debugfs

[Meijing Zhao]

From: Meijing Zhao <zhaomeijing@xxxxxxxxxxx>

Commit 493f349e38d0 ("memblock: Add flags and nid info in memblock
debugfs") made memblock_debug_show() stop after finding the first set
flag. A memblock region can carry multiple flags, so the remaining flags
are hidden from debugfs.

Walk all bits in the region flags and print every set flag separated by
"|". Keep walking beyond flagname[] so that a set flag without a known
name is reported as UNKNOWN rather than silently ignored.

Fixes: 493f349e38d0 ("memblock: Add flags and nid info in memblock debugfs")
Signed-off-by: Meijing Zhao <zhaomeijing@xxxxxxxxxxx>
---
Changes in v3:
- Rebase onto v7.3-rc1 and send the former patch 2/3 as a standalone
  patch.
- Move flags and first into the reg->flags block.
- Remove the redundant flagname[j] NULL check.
- Keep the existing NONE output unchanged.
- Drop the debugfs synchronization change. As discussed during the v2
  review, proper locking for runtime memblock accesses needs a broader
  design and will be addressed separately.

v2: https://lore.kernel.org/linux-mm/20260821020910.3428585-1-zhaomeijing100@xxxxxxxxx/

 mm/memblock.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 9ce86349a29f..021db49eb7fc 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -2908,14 +2908,18 @@ static int memblock_debug_show(struct seq_file *m, void *private)
 		else
 			seq_printf(m, "%4c ", 'x');
 		if (reg->flags) {
-			for (j = 0; j < count; j++) {
-				if (reg->flags & (1U << j)) {
-					seq_printf(m, "%s\n", flagname[j]);
-					break;
-				}
+			unsigned int flags = reg->flags;
+			bool first = true;
+
+			for (j = 0; flags; j++, flags >>= 1) {
+				if (!(flags & 1))
+					continue;
+				if (!first)
+					seq_putc(m, '|');
+				seq_puts(m, j < count ? flagname[j] : "UNKNOWN");
+				first = false;
 			}
-			if (j == count)
-				seq_printf(m, "%s\n", "UNKNOWN");
+			seq_putc(m, '\n');
 		} else {
 			seq_printf(m, "%s\n", "NONE");
 		}
-- 
2.25.1