[2/3] 2.6.22-rc2: known regressions v2

Ingo Molnar mingo at elte.hu
Fri May 25 06:11:05 EDT 2007

* Linus Torvalds <torvalds at linux-foundation.org> wrote:

> > i very much agree that this kmalloc_index() one shouldnt be called a 
> > "BUG: ", but if you look at the majority of WARN_ON() instances they 
> > are checks for clear, serious kernel bugs.
> I _still_ disagree.
> There's a huge difference between "You killed my father, prepare to 
> die", and "Btw, I didn't like that, but I'll just continue".

yeah ...

> And that's the difference between BUG_ON() and WARN_ON().

how about this solution: make WARN_ON() a "WARNING: " like you suggested 
(i still agree with that in principle), but also solve the additional 
problem i'm trying to outline: make BUG_ON() _not_ crash the box [only 
if the user asks for a crash to happen in such circumstances - this can 
be a sysctl.]. Then i can change the majority of the current WARN_ON()s 
to BUG_ON()s.

Most of the WARN_ON()s i personally add (and most of the WARN_ON()s i 
see others adding) are not WARN_ON()s because "i didnt like that and 
i'll just continue", they are WARN_ON() because i want _actual feedback 
from users_.

A BUG_ON() has a (much) lower likelyhood of being reported back - for 
most users it is a "X just hung hard, there was nothing in the syslog, i 
had to switch back to the older kernel" experience, and they do not have 
a serial console to hook up (newer hardware often doesnt even have a 
serial port). With the WARN_ON()s we have a _chance_ that despite the 
seriousness of the bug, the message makes it to the syslog, until the 
system comes to a screeching halt due to side-effects of the bug.

in that sense i am part of the problem: i was adding WARN_ON()s that 
werent true 'warnings' but 'bugs'. So i'd very much like to fix that 
problem, but i'd also like to solve the (very serious and existing) 
problem of BUG_ON()s making it less likely to get bugs reported back. 


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