From 96c6a32ccb55a366054fd82cc63523bb7f7493d3 Mon Sep 17 00:00:00 2001 From: Dmitry Vyukov Date: Tue, 21 Aug 2018 21:55:24 -0700 Subject: [PATCH] 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 Acked-by: Greg Kroah-Hartman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/asm-generic/bug.h | 16 +++++++++++++--- 1 file 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) -- GitLab