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Date: Mon, 27 Jul 2020 15:17:31 +0200 From: Ingo Molnar <mingo@...nel.org> To: peterz@...radead.org Cc: Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, npiggin@...il.com, x86@...nel.org, linux-sh@...r.kernel.org, borntraeger@...ibm.com, jcmvbkbc@...il.com Subject: Re: [PATCH] lockdep: Fix TRACE_IRQFLAGS vs NMIs * peterz@...radead.org <peterz@...radead.org> wrote: > > 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 their NMI entry ] > > However, that commit explicitly changed lockdep_hardirqs_*() to ignore > lockdep_off() and breaks every architecture that has irq-tracing in > it's NMI entry that hasn't been fixed up (x86 being the only fixed one > at this point). > > The reason for this change is that by ignoring lockdep_off() we can: > > - get rid of 'current->lockdep_recursion' in lockdep_assert_irqs*() > which was going to to give header-recursion issues with the > seqlock rework. > > - allow these lockdep_assert_*() macros to function in NMI context. > > Restore the previous state of things and allow an architecture to > opt-in to the NMI IRQ tracking support, however instead of relying on > lockdep_off(), rely on in_nmi(), both are part of nmi_enter() and so > over-all entry ordering doesn't need to change. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org> > --- > arch/x86/Kconfig.debug | 3 +++ > kernel/locking/lockdep.c | 8 +++++++- > lib/Kconfig.debug | 6 ++++++ > 3 files changed, 16 insertions(+), 1 deletion(-) Tree management side note: to apply this I've created a new tip:locking/nmi branch, which is based off the existing NMI vs. IRQ tracing commits included in locking/core: ed00495333cc: ("locking/lockdep: Fix TRACE_IRQFLAGS vs. NMIs") ba1f2b2eaa2a: ("x86/entry: Fix NMI vs IRQ state tracking") 859d069ee1dd: ("lockdep: Prepare for NMI IRQ state tracking") 248591f5d257: ("kcsan: Make KCSAN compatible with new IRQ state tracking") e1bcad609f5a: ("Merge branch 'tip/x86/entry'") b037b09b9058: ("x86/entry: Rename idtentry_enter/exit_cond_rcu() to idtentry_enter/exit()") dcb7fd82c75e: ("Linux 5.8-rc4") This locking/nmi branch can then be merged into irq/entry (there's a bunch of conflicts between them), without coupling all of v5.9's locking changes to Thomas's generic entry work. Thanks, Ingo
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