On Wed, Sep 23, 2020 at 11:52:51AM -0400, Steven Rostedt wrote:
> On Wed, 23 Sep 2020 10:40:32 +0200
> pet...@infradead.org wrote:
>
> > However, with migrate_disable() we can have each task preempted in a
> > migrate_disable() region, worse we can stack them all on the _same_ CPU
> > (super ridic
On Mon, Sep 21, 2020 at 09:27:57PM +0200, Thomas Gleixner wrote:
> Alternatively this could of course be solved with per CPU page tables
> which will come around some day anyway I fear.
Previously (with PTI) we looked at making the entire kernel map per-CPU,
and that takes a 2K copy on switch_mm()
On Mon, Sep 21, 2020 at 09:27:57PM +0200, Thomas Gleixner wrote:
> On Mon, Sep 21 2020 at 09:24, Linus Torvalds wrote:
> > On Mon, Sep 21, 2020 at 12:39 AM Thomas Gleixner wrote:
> >>
> >> If a task is migrated to a different CPU then the mapping address will
> >> change which will explode in colo
On Tue, Sep 15, 2020 at 08:06:59PM +0200, Michal Suchanek wrote:
> This reverts commit 116ac378bb3ff844df333e7609e7604651a0db9d.
>
> This commit causes the kernel to oops and reboot when injecting a SLB
> multihit which causes a MCE.
>
> Before this commit a SLB multihit was corrected by the kern
On Mon, Sep 14, 2020 at 02:52:16PM +1000, Nicholas Piggin wrote:
> Reading and modifying current->mm and current->active_mm and switching
> mm should be done with irqs off, to prevent races seeing an intermediate
> state.
>
> This is similar to commit 38cf307c1f20 ("mm: fix kthread_use_mm() vs TLB
On Thu, Sep 10, 2020 at 06:59:21PM -0300, Jason Gunthorpe wrote:
> So, I suggest pXX_offset_unlocked()
Urgh, no. Elsewhere in gup _unlocked() means it will take the lock
itself (get_user_pages_unlocked()) -- although often it seems to mean
the lock is already held (git grep _unlocked and marvel).
On Tue, Sep 08, 2020 at 12:50:44PM -0400, Qian Cai wrote:
> > No, you're talking nonsense. We must not free @mm when
> > 'current->active_mm == mm', never.
>
> Yes, you are right. It still trigger this below on powerpc with today's
> linux-next by fuzzing for a while (saw a few times on recent lin
On Fri, Aug 28, 2020 at 08:00:19PM +1000, Nicholas Piggin wrote:
> Closing this race only requires interrupts to be disabled while ->mm
> and ->active_mm are being switched, but the TLB problem requires also
> holding interrupts off over activate_mm. Unfortunately not all archs
> can do that yet,
On Wed, Aug 19, 2020 at 05:32:50PM +0200, pet...@infradead.org wrote:
> On Wed, Aug 19, 2020 at 08:39:13PM +1000, Alexey Kardashevskiy wrote:
>
> > > or current upstream?
> >
> > The upstream 18445bf405cb (13 hours old) also shows the problem. Yours
> > 1/2 still fixes it.
>
> Afaict that just r
On Wed, Aug 19, 2020 at 08:39:13PM +1000, Alexey Kardashevskiy wrote:
> > or current upstream?
>
> The upstream 18445bf405cb (13 hours old) also shows the problem. Yours
> 1/2 still fixes it.
Afaict that just reduces the window.
Isn't the problem that:
arch/powerpc/kernel/exceptions-64e.S
On Tue, Aug 18, 2020 at 05:22:33PM +1000, Nicholas Piggin wrote:
> Excerpts from pet...@infradead.org's message of August 12, 2020 8:35 pm:
> > On Wed, Aug 12, 2020 at 06:18:28PM +1000, Nicholas Piggin wrote:
> >> Excerpts from pet...@infradead.org's message of August 7, 2020 9:11 pm:
> >> >
> >>
On Wed, Aug 12, 2020 at 06:18:28PM +1000, Nicholas Piggin wrote:
> Excerpts from pet...@infradead.org's message of August 7, 2020 9:11 pm:
> >
> > What's wrong with something like this?
> >
> > AFAICT there's no reason to actually try and add IRQ tracing here, it's
> > just a hand full of instruc
What's wrong with something like this?
AFAICT there's no reason to actually try and add IRQ tracing here, it's
just a hand full of instructions at the most.
---
diff --git a/arch/powerpc/include/asm/hw_irq.h
b/arch/powerpc/include/asm/hw_irq.h
index 3a0db7b0b46e..6be22c1838e2 100644
--- a/arc
On Thu, Aug 06, 2020 at 10:25:12PM +1000, Michael Ellerman wrote:
> pet...@infradead.org writes:
> > On Thu, Aug 06, 2020 at 03:32:25PM +1000, Michael Ellerman wrote:
> >
> >> That brings with it a bunch of problems, such as existing software that
> >> has been developed/configured for Power8 and e
On Thu, Aug 06, 2020 at 03:32:25PM +1000, Michael Ellerman wrote:
> That brings with it a bunch of problems, such as existing software that
> has been developed/configured for Power8 and expects to see SMT8.
>
> We also allow LPARs to be live migrated from Power8 to Power9 (and back), so
> mainta
On Tue, Aug 04, 2020 at 05:40:07PM +0530, Srikar Dronamraju wrote:
> * pet...@infradead.org [2020-08-04 12:45:20]:
>
> > On Tue, Aug 04, 2020 at 09:03:06AM +0530, Srikar Dronamraju wrote:
> > > cpu_smt_mask tracks topology_sibling_cpumask. This would be good for
> > > most architectures. One of t
On Tue, Aug 04, 2020 at 09:03:07AM +0530, Srikar Dronamraju wrote:
> On Power9 a pair of cores can be presented by the firmware as a big-core
> for backward compatibility reasons, with 4 threads per (small) core and 8
> threads per big-core. cpu_smt_mask() should generally point to the cpu mask
> o
On Tue, Aug 04, 2020 at 09:03:06AM +0530, Srikar Dronamraju wrote:
> cpu_smt_mask tracks topology_sibling_cpumask. This would be good for
> most architectures. One of the users of cpu_smt_mask(), would be to
> identify idle-cores. On Power9, a pair of cores can be presented by the
> firmware as a b
Prior to commit 859d069ee1dd ("lockdep: Prepare for NMI IRQ state
tracking") IRQ state tracking was disabled in NMIs due to nmi_enter()
doing lockdep_off() -- with the obvious requirement that NMI entry
call nmi_enter() before trace_hardirqs_off().
[ afaict, PowerPC and SH violate this order on
On Sun, Jul 26, 2020 at 02:14:34PM +1000, Nicholas Piggin wrote:
> Excerpts from Peter Zijlstra's message of July 26, 2020 6:26 am:
> > Which is 'funny' when it interleaves like:
> >
> > local_irq_disable();
> > ...
> > local_irq_enable()
> > trace_hardirqs_on();
> >
> >
On Sun, Jul 26, 2020 at 02:14:34PM +1000, Nicholas Piggin wrote:
> > Now, x86, and at least arm64 call nmi_enter() before
> > trace_hardirqs_off(), but AFAICT Power never did that, and that's part
> > of the problem. nmi_enter() does lockdep_off() and that _used_ to also
> > kill IRQ tracking.
>
>
On Thu, Jul 23, 2020 at 03:04:13PM -0400, Waiman Long wrote:
> On 7/23/20 2:47 PM, pet...@infradead.org wrote:
> > On Thu, Jul 23, 2020 at 02:32:36PM -0400, Waiman Long wrote:
> > > BTW, do you have any comment on my v2 lock holder cpu info qspinlock
> > > patch?
> > > I will have to update the pa
On Thu, Jul 23, 2020 at 02:32:36PM -0400, Waiman Long wrote:
> BTW, do you have any comment on my v2 lock holder cpu info qspinlock patch?
> I will have to update the patch to fix the reported 0-day test problem, but
> I want to collect other feedback before sending out v3.
I want to say I hate it
On Wed, Jul 22, 2020 at 10:48:54AM +0200, Peter Zijlstra wrote:
> But reading your explanation, it looks like the Linux topology setup
> could actually unravel the fused-faux-SMT8 into two independent SMT4
> parts, negating that firmware option.
Ah, it looks like that's exactly what you're doing.
On Tue, Jul 21, 2020 at 05:08:10PM +0530, Srikar Dronamraju wrote:
> Currently "CACHE" domain happens to be the 2nd sched domain as per
> powerpc_topology. This domain will collapse if cpumask of l2-cache is
> same as SMT domain. However we could generalize this domain such that it
> could mean eit
On Tue, Jul 21, 2020 at 08:04:27PM +1000, Nicholas Piggin wrote:
> That being said, the x86 sync core gap that I imagined could be fixed
> by changing to rq->curr == rq->idle test does not actually exist because
> the global membarrier does not have a sync core option. So fixing the
> exit_lazy_t
On Thu, Jul 16, 2020 at 08:03:36PM +1000, Nicholas Piggin wrote:
> Excerpts from Peter Zijlstra's message of July 16, 2020 6:50 pm:
> > On Wed, Jul 15, 2020 at 10:18:20PM -0700, Andy Lutomirski wrote:
> >> > On Jul 15, 2020, at 9:15 PM, Nicholas Piggin wrote:
> >> But I’m wondering if all this de
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