Hi Alex, Thank you for the patch. On Sun, Apr 14, 2024 at 12:08:50PM -0500, Alex Elder wrote: > Several times recently Greg KH has admonished that variants of WARN() > should not be used, because when the panic_on_warn kernel option is set, > their use can lead to a panic. His reasoning was that the majority of > Linux instances (including Android and cloud systems) run with this option > enabled. And therefore a condition leading to a warning will frequently > cause an undesirable panic. > > The "coding-style.rst" document says not to worry about this kernel > option. Update it to provide a more nuanced explanation. > > Signed-off-by: Alex Elder <elder@xxxxxxxxxx> > --- > Documentation/process/coding-style.rst | 21 +++++++++++---------- > 1 file changed, 11 insertions(+), 10 deletions(-) > > diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst > index 9c7cf73473943..bce43b01721cb 100644 > --- a/Documentation/process/coding-style.rst > +++ b/Documentation/process/coding-style.rst > @@ -1235,17 +1235,18 @@ example. Again: WARN*() must not be used for a condition that is expected > to trigger easily, for example, by user space actions. pr_warn_once() is a > possible alternative, if you need to notify the user of a problem. > > -Do not worry about panic_on_warn users > -************************************** > +The panic_on_warn kernel option > +******************************** > > -A few more words about panic_on_warn: Remember that ``panic_on_warn`` is an > -available kernel option, and that many users set this option. This is why > -there is a "Do not WARN lightly" writeup, above. However, the existence of > -panic_on_warn users is not a valid reason to avoid the judicious use > -WARN*(). That is because, whoever enables panic_on_warn has explicitly > -asked the kernel to crash if a WARN*() fires, and such users must be > -prepared to deal with the consequences of a system that is somewhat more > -likely to crash. > +Note that ``panic_on_warn`` is an available kernel option. If it is enabled, > +a WARN*() call whose condition holds leads to a kernel panic. Many users > +(including Android and many cloud providers) set this option, and this is > +why there is a "Do not WARN lightly" writeup, above. > + > +The existence of this option is not a valid reason to avoid the judicious > +use of warnings. There are other options: ``dev_warn*()`` and ``pr_warn*()`` > +issue warnings but do **not** cause the kernel to crash. Use these if you > +want to prevent such panics. Those options are not equivalent, they print a single message, which is much easier to ignore. WARN() is similar to -Werror in some sense, it pushes vendors to fix the warnings. I have used WARN() in the past to indicate usage of long-deprecated APIs that we were getting close to removing for instance. dev_warn() wouldn't have had the same effect. > > Use BUILD_BUG_ON() for compile-time assertions > ********************************************** -- Regards, Laurent Pinchart
