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Date: Mon, 15 Jun 2020 13:00:35 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: tglx@...utronix.de, x86@...nel.org, elver@...gle.com,
kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
will@...nel.org, dvyukov@...gle.com, glider@...gle.com,
andreyknvl@...gle.com
Subject: Re: [PATCH 2/9] rcu: Fixup noinstr warnings
On Mon, Jun 15, 2020 at 10:14:04AM -0700, Paul E. McKenney wrote:
> On Mon, Jun 15, 2020 at 06:24:27PM +0200, Peter Zijlstra wrote:
> > On Mon, Jun 15, 2020 at 05:55:13PM +0200, Peter Zijlstra wrote:
> > > On Mon, Jun 15, 2020 at 05:49:05PM +0200, Peter Zijlstra wrote:
> > > > @@ -983,13 +993,17 @@ noinstr void rcu_nmi_enter(void)
> > > > if (!in_nmi())
> > > > rcu_cleanup_after_idle();
> > > >
> > > > + instrumentation_begin();
> > > > + // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
> > > > + instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks));
> > > > + // instrumentation for the noinstr rcu_dynticks_eqs_exit()
> > > > + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> > > > +
> > > > incby = 1;
> > > > } else if (!in_nmi()) {
> > > > instrumentation_begin();
> > > > rcu_irq_enter_check_tick();
> > > > - instrumentation_end();
> > > > }
> > > > - instrumentation_begin();
> > > > trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
> > > > rdp->dynticks_nmi_nesting,
> > > > rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));
> > >
> > > Oh, that's lost a possible instrumentation_begin() :/ But weirdly
> > > objtool didn't complain about that... Let me poke at that.
>
> This merge window has been quite the trainwreck, hasn't it? :-/
>
> > Like so then...
>
> Looks plausible, firing up some tests.
And it passes light rcutorture testing across all the scenarios.
So looks even more plausible. ;-)
Thanx, Paul
> > ---
> > Subject: rcu: Fixup noinstr warnings
> >
> > A KCSAN build revealed we have explicit annoations through atomic_*()
> > usage, switch to arch_atomic_*() for the respective functions.
> >
> > vmlinux.o: warning: objtool: rcu_nmi_exit()+0x4d: call to __kcsan_check_access() leaves .noinstr.text section
> > vmlinux.o: warning: objtool: rcu_dynticks_eqs_enter()+0x25: call to __kcsan_check_access() leaves .noinstr.text section
> > vmlinux.o: warning: objtool: rcu_nmi_enter()+0x4f: call to __kcsan_check_access() leaves .noinstr.text section
> > vmlinux.o: warning: objtool: rcu_dynticks_eqs_exit()+0x2a: call to __kcsan_check_access() leaves .noinstr.text section
> > vmlinux.o: warning: objtool: __rcu_is_watching()+0x25: call to __kcsan_check_access() leaves .noinstr.text section
> >
> > Additionally, without the NOP in instrumentation_begin(), objtool would
> > not detect the lack of the 'else instrumentation_begin();' branch in
> > rcu_nmi_enter().
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > ---
> > include/linux/compiler.h | 2 +-
> > kernel/rcu/tree.c | 33 +++++++++++++++++++++++++--------
> > 2 files changed, 26 insertions(+), 9 deletions(-)
> >
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -123,7 +123,7 @@ void ftrace_likely_update(struct ftrace_
> > #ifdef CONFIG_DEBUG_ENTRY
> > /* Begin/end of an instrumentation safe region */
> > #define instrumentation_begin() ({ \
> > - asm volatile("%c0:\n\t" \
> > + asm volatile("%c0: nop\n\t" \
> > ".pushsection .discard.instr_begin\n\t" \
> > ".long %c0b - .\n\t" \
> > ".popsection\n\t" : : "i" (__COUNTER__)); \
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -250,7 +250,7 @@ static noinstr void rcu_dynticks_eqs_ent
> > * next idle sojourn.
> > */
> > rcu_dynticks_task_trace_enter(); // Before ->dynticks update!
> > - seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
> > + seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
> > // RCU is no longer watching. Better be in extended quiescent state!
> > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> > (seq & RCU_DYNTICK_CTRL_CTR));
> > @@ -274,13 +274,13 @@ static noinstr void rcu_dynticks_eqs_exi
> > * and we also must force ordering with the next RCU read-side
> > * critical section.
> > */
> > - seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
> > + seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
> > // RCU is now watching. Better not be in an extended quiescent state!
> > rcu_dynticks_task_trace_exit(); // After ->dynticks update!
> > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> > !(seq & RCU_DYNTICK_CTRL_CTR));
> > if (seq & RCU_DYNTICK_CTRL_MASK) {
> > - atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
> > + arch_atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
> > smp_mb__after_atomic(); /* _exit after clearing mask. */
> > }
> > }
> > @@ -313,7 +313,7 @@ static __always_inline bool rcu_dynticks
> > {
> > struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> >
> > - return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
> > + return !(arch_atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
> > }
> >
> > /*
> > @@ -633,6 +633,10 @@ static noinstr void rcu_eqs_enter(bool u
> > do_nocb_deferred_wakeup(rdp);
> > rcu_prepare_for_idle();
> > rcu_preempt_deferred_qs(current);
> > +
> > + // instrumentation for the noinstr rcu_dynticks_eqs_enter()
> > + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> > +
> > instrumentation_end();
> > WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
> > // RCU is watching here ...
> > @@ -692,6 +696,7 @@ noinstr void rcu_nmi_exit(void)
> > {
> > struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> >
> > + instrumentation_begin();
> > /*
> > * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
> > * (We are exiting an NMI handler, so RCU better be paying attention
> > @@ -705,7 +710,6 @@ noinstr void rcu_nmi_exit(void)
> > * leave it in non-RCU-idle state.
> > */
> > if (rdp->dynticks_nmi_nesting != 1) {
> > - instrumentation_begin();
> > trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
> > atomic_read(&rdp->dynticks));
> > WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
> > @@ -714,13 +718,15 @@ noinstr void rcu_nmi_exit(void)
> > return;
> > }
> >
> > - instrumentation_begin();
> > /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
> > trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
> > WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
> >
> > if (!in_nmi())
> > rcu_prepare_for_idle();
> > +
> > + // instrumentation for the noinstr rcu_dynticks_eqs_enter()
> > + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> > instrumentation_end();
> >
> > // RCU is watching here ...
> > @@ -838,6 +844,10 @@ static void noinstr rcu_eqs_exit(bool us
> > rcu_dynticks_eqs_exit();
> > // ... but is watching here.
> > instrumentation_begin();
> > +
> > + // instrumentation for the noinstr rcu_dynticks_eqs_exit()
> > + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> > +
> > rcu_cleanup_after_idle();
> > trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks));
> > WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
> > @@ -983,13 +993,20 @@ noinstr void rcu_nmi_enter(void)
> > if (!in_nmi())
> > rcu_cleanup_after_idle();
> >
> > + instrumentation_begin();
> > + // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
> > + instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks));
> > + // instrumentation for the noinstr rcu_dynticks_eqs_exit()
> > + instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> > +
> > incby = 1;
> > } else if (!in_nmi()) {
> > instrumentation_begin();
> > rcu_irq_enter_check_tick();
> > - instrumentation_end();
> > + } else {
> > + instrumentation_begin();
> > }
> > - instrumentation_begin();
> > +
> > trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
> > rdp->dynticks_nmi_nesting,
> > rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));
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