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authorDmitry Vyukov <dvyukov@google.com>2018-08-22 07:55:24 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2018-08-22 20:52:46 +0300
commit96c6a32ccb55a366054fd82cc63523bb7f7493d3 (patch)
treefb339e055035609ea3616e64a5a4262ccf20da65
parent23c85094fe1895caefdd19ef624ee687ec5f4507 (diff)
downloadlinux-96c6a32ccb55a366054fd82cc63523bb7f7493d3.tar.xz
include/asm-generic/bug.h: clarify valid uses of WARN()
Explicitly state that WARN*() should be used only for recoverable kernel issues/bugs and that it should not be used for any kind of invalid external inputs or transient conditions. Motivation: it's a very useful capability to be able to understand if a particular kernel splat means a kernel bug or simply an invalid user-space program. For the former one wants to notify kernel developers, while notifying kernel developers for the latter is annoying. Even a kernel developer may not know what to do with a WARNING in an unfamiliar subsystem. This is especially critical for any automated testing systems that may use panic_on_warn and mail kernel developers. The clear separation also serves as an additional documentation: is it a condition that must never occur because of additional checks/logic elsewhere? or is it simply a check for invalid inputs or unfortunate conditions? Use of pr_err() for user messages also leads to better error messages. "Something is wrong in file foo on line X" is not particularly useful message for end user. pr_err() forces developers to write more meaningful error messages for user. As of now we are almost there. We are doing systematic kernel testing with panic_on_warn and are not seeing massive amounts of false positives. But every now and then another WARN on ENOMEM or invalid inputs pops up and leads to a lengthy argument each time. The goal of this change is to officially document the rules. Link: http://lkml.kernel.org/r/20180620103716.61636-1-dvyukov@gmail.com Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/asm-generic/bug.h16
1 files changed, 13 insertions, 3 deletions
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index a7613e1b0c87..20561a60db9c 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -75,9 +75,19 @@ struct bug_entry {
/*
* 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.
+ * significant kernel issues that need prompt attention if they should ever
+ * appear at runtime.
+ *
+ * Do not use these macros when checking for invalid external inputs
+ * (e.g. invalid system call arguments, or invalid data coming from
+ * network/devices), and on transient conditions like ENOMEM or EAGAIN.
+ * These macros should be used for recoverable kernel issues only.
+ * For invalid external inputs, transient conditions, etc use
+ * pr_err[_once/_ratelimited]() followed by dump_stack(), if necessary.
+ * Do not include "BUG"/"WARNING" in format strings manually to make these
+ * conditions distinguishable from kernel issues.
+ *
+ * Use the versions with printk format strings to provide better diagnostics.
*/
#ifndef __WARN_TAINT
extern __printf(3, 4)