Messages in this thread | | | Subject | Re: possible lockdep regression introduced by 4d004099a668 ("lockdep: Fix lockdep recursion") | From | Filipe Manana <> | Date | Tue, 3 Nov 2020 10:22:59 +0000 |
| |
On 03/11/20 10:15, Jan Kara wrote: > On Mon 02-11-20 17:58:54, Filipe Manana wrote: >> >> >> On 26/10/20 15:22, Peter Zijlstra wrote: >>> On Mon, Oct 26, 2020 at 01:55:24PM +0100, Peter Zijlstra wrote: >>>> On Mon, Oct 26, 2020 at 11:56:03AM +0000, Filipe Manana wrote: >>>>>> That smells like the same issue reported here: >>>>>> >>>>>> https://lkml.kernel.org/r/20201022111700.GZ2651@hirez.programming.kicks-ass.net >>>>>> >>>>>> Make sure you have commit: >>>>>> >>>>>> f8e48a3dca06 ("lockdep: Fix preemption WARN for spurious IRQ-enable") >>>>>> >>>>>> (in Linus' tree by now) and do you have CONFIG_DEBUG_PREEMPT enabled? >>>>> >>>>> Yes, CONFIG_DEBUG_PREEMPT is enabled. >>>> >>>> Bummer :/ >>>> >>>>> I'll try with that commit and let you know, however it's gonna take a >>>>> few hours to build a kernel and run all fstests (on that test box it >>>>> takes over 3 hours) to confirm that fixes the issue. >>>> >>>> *ouch*, 3 hours is painful. How long to make it sick with the current >>>> kernel? quicker I would hope? >>>> >>>>> Thanks for the quick reply! >>>> >>>> Anyway, I don't think that commit can actually explain the issue :/ >>>> >>>> The false positive on lockdep_assert_held() happens when the recursion >>>> count is !0, however we _should_ be having IRQs disabled when >>>> lockdep_recursion > 0, so that should never be observable. >>>> >>>> My hope was that DEBUG_PREEMPT would trigger on one of the >>>> __this_cpu_{inc,dec}(lockdep_recursion) instance, because that would >>>> then be a clear violation. >>>> >>>> And you're seeing this on x86, right? >>>> >>>> Let me puzzle moar.. >>> >>> So I might have an explanation for the Sparc64 fail, but that can't >>> explain x86 :/ >>> >>> I initially thought raw_cpu_read() was OK, since if it is !0 we have >>> IRQs disabled and can't get migrated, so if we get migrated both CPUs >>> must have 0 and it doesn't matter which 0 we read. >>> >>> And while that is true; it isn't the whole store, on pretty much all >>> architectures (except x86) this can result in computing the address for >>> one CPU, getting migrated, the old CPU continuing execution with another >>> task (possibly setting recursion) and then the new CPU reading the value >>> of the old CPU, which is no longer 0. >>> >>> I already fixed a bunch of that in: >>> >>> baffd723e44d ("lockdep: Revert "lockdep: Use raw_cpu_*() for per-cpu variables"") >>> >>> but clearly this one got crossed. >>> >>> Still, that leaves me puzzled over you seeing this on x86 :/ >> >> Hi Peter, >> >> I still get the same issue with 5.10-rc2. >> Is there any non-merged patch I should try, or anything I can help with? > > BTW, I've just hit the same deadlock issue with ext4 on generic/390 so I > confirm this isn't btrfs specific issue (as we already knew from the > analysis but still it's good to have that confirmed).
Indeed, yesterday Darrick was mentioning on IRC that he has run into it too with fstests on XFS (5.10-rc).
> > Honza >
| |