From: Dmitry Vyukov <dvyukov@gmail.com>
To: linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org,
akpm@linux-foundation.org, torvalds@linux-foundation.org
Cc: Dmitry Vyukov <dvyukov@google.com>
Subject: [PATCH] include/asm-generic/bug.h: clarify valid uses of WARN()
Date: Wed, 20 Jun 2018 12:37:16 +0200 [thread overview]
Message-ID: <20180620103716.61636-1-dvyukov@gmail.com> (raw)
From: Dmitry Vyukov <dvyukov@google.com>
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.
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
---
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)
--
2.18.0.rc1.244.gcf134e6275-goog
next reply other threads:[~2018-06-20 10:37 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-20 10:37 Dmitry Vyukov [this message]
2018-06-21 0:02 ` [PATCH] include/asm-generic/bug.h: clarify valid uses of WARN() Greg KH
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180620103716.61636-1-dvyukov@gmail.com \
--to=dvyukov@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=dvyukov@google.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).