documentation: when to BUG(), and when to not BUG()
Provide some basic advice about when to use BUG()/BUG_ON(): never, unless
there's really no better option.
This matches my understanding of the standard policy ... which seems not
to be written down so far, outside of LKML messages that I haven't
bookmarked.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Hans Verkuil <hverkuil@xs4all.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 8af2763..37b82cb 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -28,6 +28,17 @@
#define BUGFLAG_WARNING (1<<0)
#endif /* CONFIG_GENERIC_BUG */
+/*
+ * Don't use BUG() or BUG_ON() unless there's really no way out; one
+ * example might be detecting data structure corruption in the middle
+ * of an operation that can't be backed out of. If the (sub)system
+ * can somehow continue operating, perhaps with reduced functionality,
+ * it's probably not BUG-worthy.
+ *
+ * If you're tempted to BUG(), think again: is completely giving up
+ * really the *only* solution? There are usually better options, where
+ * users don't need to reboot ASAP and can mostly shut down cleanly.
+ */
#ifndef HAVE_ARCH_BUG
#define BUG() do { \
printk("BUG: failure at %s:%d/%s()!\n", __FILE__, __LINE__, __func__); \
@@ -39,6 +50,12 @@
#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while(0)
#endif
+/*
+ * WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report
+ * significant issues that need prompt attention if they should ever
+ * appear at runtime. Use the versions with printk format strings
+ * to provide better diagnostics.
+ */
#ifndef __WARN
#ifndef __ASSEMBLY__
extern void warn_slowpath(const char *file, const int line,
