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[193.116.193.175]) by smtp.gmail.com with ESMTPSA id q12sm27030752pfg.135.2020.08.18.16.55.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2020 16:55:02 -0700 (PDT) Date: Wed, 19 Aug 2020 09:54:57 +1000 From: Nicholas Piggin Subject: Re: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled synchronisation with actual irq state To: peterz@infradead.org Cc: Alexey Kardashevskiy , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Ingo Molnar , Will Deacon References: <20200723105615.1268126-1-npiggin@gmail.com> <20200807111126.GI2674@hirez.programming.kicks-ass.net> <1597220073.mbvcty6ghk.astroid@bobo.none> <20200812103530.GL2674@hirez.programming.kicks-ass.net> <1597735273.s0usqkrlsk.astroid@bobo.none> <20200818154143.GT2674@hirez.programming.kicks-ass.net> In-Reply-To: <20200818154143.GT2674@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Message-Id: <1597793862.l8c4pmmzpq.astroid@bobo.none> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: linux-arch-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Excerpts from peterz@infradead.org's message of August 19, 2020 1:41 am: > On Tue, Aug 18, 2020 at 05:22:33PM +1000, Nicholas Piggin wrote: >> Excerpts from peterz@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 peterz@infradead.org's message of August 7, 2020 9:11 p= m: >> >> >=20 >> >> > What's wrong with something like this? >> >> >=20 >> >> > AFAICT there's no reason to actually try and add IRQ tracing here, = it's >> >> > just a hand full of instructions at the most. >> >>=20 >> >> Because we may want to use that in other places as well, so it would >> >> be nice to have tracing. >> >>=20 >> >> Hmm... also, I thought NMI context was free to call local_irq_save/re= store >> >> anyway so the bug would still be there in those cases? >> >=20 >> > NMI code has in_nmi() true, in which case the IRQ tracing is disabled >> > (except for x86 which has CONFIG_TRACE_IRQFLAGS_NMI). >> >=20 >>=20 >> That doesn't help. It doesn't fix the lockdep irq state going out of >> synch with the actual irq state. The code which triggered this with the >> special powerpc irq disable has in_nmi() true as well. >=20 > Urgh, you're talking about using lockdep_assert_irqs*() from NMI > context? >=20 > If not, I'm afraid I might've lost the plot a little on what exact > failure case we're talking about. >=20 Hm, I may have been a bit confused actually. Since your Fix=20 TRACE_IRQFLAGS vs NMIs patch it might now work. I'm worried powerpc disables trace irqs trace_hardirqs_off() before nmi_enter() might still be a problem, but not sure actually. Alexey did you end up re-testing with Peter's patch or current upstream? Thanks, Nick