On Sat, 2014-12-27 at 10:52 -0500, Sasha Levin wrote: > On 12/27/2014 04:52 AM, Davidlohr Bueso wrote: > >> Hello， > >> > Does ACCESS_ONCE() can help this issue? I have no evidence that its lack > >> > is > >> > responsible for the issue, but I think here need it indeed. Is that > >> > right? > >> > > >> > SPIN_BUG_ON(ACCESS_ONCE(lock->owner) == current, "recursion"); > > Hmm I guess on a contended spinlock, there's a chance that lock->owner > > can change, if the contended lock is acquired, right between the 'cond' > > and spin_debug(), which would explain the bogus ->owner related > > messages. Of course the same applies to ->owner_cpu. Your ACCESS_ONCE, > > however, doesn't really change anything since we still read ->owner > > again in spin_debug; How about something like this (untested)?
I guess we'd need a writer rwlock counterpart too. > There's a chance that lock->owner would change, but how would you explain > it changing to 'current'? So yeah, the above only deals with the weird printk values, not the actual issue that triggers the BUG_ON. Lets sort this out first and at least get correct data. > That is, what race condition specifically creates the > 'lock->owner == current' situation in the debug check? Why do you suspect a race as opposed to a legitimate recursion issue? Although after staring at the code for a while, I cannot see foul play in sched_rr_get_interval. Given that all reports show bogus contending CPU and .owner_cpu, I do wonder if this is actually a symptom of the BUG_ON where something fishy is going on.. although I have no evidence to support that. I also ran into this https://lkml.org/lkml/2014/11/7/762 which shows the same bogus values yet a totally different stack. Sasha, I ran trinity with CONFIG_DEBUG_SPINLOCK=y all night without triggering anything. How are you hitting this? Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
