Commit b58e733f authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Paul E. McKenney
Browse files

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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent 5faafd56

include/linux/compiler.h

+1 −1
Original line number Diff line number Diff line
@@ -123,7 +123,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, 
#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__));		\

kernel/rcu/tree.c

+25 −7
Original line number Diff line number Diff line
@@ -250,7 +250,7 @@ static noinstr void rcu_dynticks_eqs_enter(void) 
	 * 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_exit(void) 
	 * 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_curr_cpu_in_eqs(void) 
{

	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 user) 
	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 user) 
	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 +993,21 @@ 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();

	}



	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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