On Wed, 6 Nov 2019 23:25:13 +0000 Russell King - ARM Linux admin <li...@armlinux.org.uk> wrote:
> On Wed, Nov 06, 2019 at 09:34:40PM +0100, Peter Zijlstra wrote: > > I suppose I'm surprised there are backtraces that are not important. > > Either badness happened and it needs printing, or the user asked for it > > and it needs printing. > > Or utterly meaningless. > > > Perhaps we should be removing backtraces if they're not important > > instead of allowing to print them as lower loglevels? > > Definitely! WARN_ON() is well overused - and as is typical, used > without much thought. Bound to happen after Linus got shirty about > BUG_ON() being over used. Everyone just grabbed the next nearest thing > to assert(). > > As a kind of example, I've recently come across one WARN_ON() in a > driver subsystem (that shall remain nameless at the moment) which very > likely has multiple different devices on a platform. The WARN_ON() > triggers as a result of a problem with the hardware, but because it's a > WARN_ON(), you've no idea which device has a problem. The backtrace is > mostly meaningless. So you know that a problem has occurred, but the > kernel prints *useless* backtrace to let you know, and totally omits > the *useful* information. > I would like to bring up a topic for the next maintainers summit (although I may not even be there), that we define a clear use of WARN_ON(). I use it only if the code does something I do not expect it to do, and is considered a bug in the code if it triggers. But it appears that some drivers use it for "oh I didn't realize this hardware does something I didn't expect". And is ignored when the warn on is triggered and reported, with "you have buggy hardware" but my hardware appears to work just fine! -- Steve
