[PATCH] lib/string: replace BUG_ON with WARN_ON_ONCE in strlcat

[Josh Law <objecting@objecting.org>]

BUG_ON() in a library function is too harsh -- it panics the kernel
when a caller passes a dest string whose length already meets or
exceeds count. This is a caller bug, not a reason to bring down the
entire system.

Replace with WARN_ON_ONCE() and a safe early return. The return value
of count signals truncation to the caller, consistent with strlcat
semantics (return >= count means the output was truncated).

This follows the guidance in include/asm-generic/bug.h which
explicitly discourages BUG_ON: "Don't use BUG() or BUG_ON() unless
there's really no way out."

Signed-off-by: Josh Law <objecting@objecting.org>
---
 lib/string.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lib/string.c b/lib/string.c
index b632c71df1a5..ae3eb192534d 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -255,8 +255,9 @@ size_t strlcat(char *dest, const char *src, size_t count)
 	size_t len = strlen(src);
 	size_t res = dsize + len;
 
-	/* This would be a bug */
-	BUG_ON(dsize >= count);
+	/* This would be a caller bug */
+	if (WARN_ON_ONCE(dsize >= count))
+		return count;
 
 	dest += dsize;
 	count -= dsize;
-- 
2.34.1