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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>
This commit is contained in:
Dmitry Vyukov 2018-08-21 21:55:24 -07:00 committed by Linus Torvalds
parent 23c85094fe
commit 96c6a32ccb
1 changed files with 13 additions and 3 deletions
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16
include/asm-generic/bug.h
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@ -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)