On Mon, Dec 14, 2015 at 06:51:41AM +0000, Duncan wrote: > Birdsarenice posted on Sun, 13 Dec 2015 22:55:19 +0000 as excerpted: > > > Meanwhile, I did get lucky: At one crash I happened to be logged in and > > was able to hit dmesg seconds before it went completely. So what I have > > here is information that looks like it'll help you track down a > > rarely-encountered and hard-to-reproduce bug which can cause the system > > to lock up completely in event of certain types of hard drive failure. > > It might be nothing, but perhaps someone will find it of use - because > > it'd be a tricky one to both reproduce and get a good error report if it > > did occur. > > > > I see an 'invalid opcode' error in here, that's pretty unusual > > Disclaimer: I'm a list regular and (small-scale) sysadmin, not a dev, > and most certainly not a btrfs dev. Take what I saw with that in mind, > tho I've been active on-list for over a year and thus now have a > reasonable level of practical sysadmin configuration and crisis recovery > level btrfs experience. > > You could well be quite correct with the unusual crash log and its value, > I'll leave that up to the devs to decide, but that "invalid opcode: 0000" > bit is in fact not at all unusual on btrfs. Tho I can say it fooled me > originally as well, because it certainly /looks/ both suspicious and in > general unusual. > > Based on how a dev explained it to me, I believe btrfs actually > deliberately uses opcode 0000 to trigger a semi-controlled crash in > instances where code that "should never happen" actually gets executed > for some reason, leaving the kernel is an unknown and thus not > trustworthy enough to reliably write to storage devices and do a > controlled shutdown. That's of course why the tracebacks are there, to > help the devs figure out where it was and what triggered it, but the 0000 > opcode itself is actually quite frequently found in these tracebacks, > because it's the method chosen to deliberately trigger them.
It's not just btrfs. Invalid opcode is the way that the kernel's BUG and BUG_ON macro is implemented. Hugo. -- Hugo Mills | Great oxymorons of the world, no. 10: hugo@... carfax.org.uk | Business Ethics http://carfax.org.uk/ | PGP: E2AB1DE4 |
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