Commit e29a4915 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Paul E. McKenney
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srcu: Debug NMI safety even on archs that don't require it 



Currently the NMI safety debugging is only performed on architectures
that don't support NMI-safe this_cpu_inc().

Reorder the code so that other architectures like x86 also detect bad
uses.

[ paulmck: Apply kernel test robot, Stephen Rothwell, and Zqiang feedback. ]

Signed-off-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent ae3c0706

include/linux/srcu.h

+24 −12
Original line number Diff line number Diff line
@@ -65,14 +65,14 @@ unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp); 
bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie);



#ifdef CONFIG_NEED_SRCU_NMI_SAFE

int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe) __acquires(ssp);

void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx, bool chknmisafe) __releases(ssp);

int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp);

void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) __releases(ssp);

#else

static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe)

static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)

{

	return __srcu_read_lock(ssp);

}

static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx, bool chknmisafe)

static inline void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)

{

	__srcu_read_unlock(ssp, idx);

}
@@ -118,6 +118,18 @@ static inline int srcu_read_lock_held(const struct srcu_struct *ssp) 


#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */



#define SRCU_NMI_UNKNOWN	0x0

#define SRCU_NMI_UNSAFE		0x1

#define SRCU_NMI_SAFE		0x2



#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_TREE_SRCU)

void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe);

#else

static inline void srcu_check_nmi_safety(struct srcu_struct *ssp,

					 bool nmi_safe) { }

#endif





/**

 * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing

 * @p: the pointer to fetch and protect for later dereferencing
@@ -175,6 +187,7 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp) 
{

	int retval;



	srcu_check_nmi_safety(ssp, false);

	retval = __srcu_read_lock(ssp);

	rcu_lock_acquire(&(ssp)->dep_map);

	return retval;
@@ -191,10 +204,8 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp 
{

	int retval;



	if (IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))

		retval = __srcu_read_lock_nmisafe(ssp, true);

	else

		retval = __srcu_read_lock(ssp);

	srcu_check_nmi_safety(ssp, true);

	retval = __srcu_read_lock_nmisafe(ssp);

	rcu_lock_acquire(&(ssp)->dep_map);

	return retval;

}
@@ -205,6 +216,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp) 
{

	int retval;



	srcu_check_nmi_safety(ssp, false);

	retval = __srcu_read_lock(ssp);

	return retval;

}
@@ -220,6 +232,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx) 
	__releases(ssp)

{

	WARN_ON_ONCE(idx & ~0x1);

	srcu_check_nmi_safety(ssp, false);

	rcu_lock_release(&(ssp)->dep_map);

	__srcu_read_unlock(ssp, idx);

}
@@ -235,17 +248,16 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) 
	__releases(ssp)

{

	WARN_ON_ONCE(idx & ~0x1);

	srcu_check_nmi_safety(ssp, true);

	rcu_lock_release(&(ssp)->dep_map);

	if (IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))

		__srcu_read_unlock_nmisafe(ssp, idx, true);

	else

		__srcu_read_unlock(ssp, idx);

	__srcu_read_unlock_nmisafe(ssp, idx);

}



/* Used by tracing, cannot be traced and cannot call lockdep. */

static inline notrace void

srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)

{

	srcu_check_nmi_safety(ssp, false);

	__srcu_read_unlock(ssp, idx);

}

include/linux/srcutree.h

+0 −4
Original line number Diff line number Diff line
@@ -43,10 +43,6 @@ struct srcu_data { 
	struct srcu_struct *ssp;

};



#define SRCU_NMI_UNKNOWN	0x0

#define SRCU_NMI_NMI_UNSAFE	0x1

#define SRCU_NMI_NMI_SAFE	0x2



/*

 * Node in SRCU combining tree, similar in function to rcu_data.

 */

kernel/rcu/srcutree.c

+10 −15
Original line number Diff line number Diff line
@@ -631,17 +631,16 @@ void cleanup_srcu_struct(struct srcu_struct *ssp) 
}

EXPORT_SYMBOL_GPL(cleanup_srcu_struct);



#ifdef CONFIG_PROVE_RCU

/*

 * Check for consistent NMI safety.

 */

static void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe)

void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe)

{

	int nmi_safe_mask = 1 << nmi_safe;

	int old_nmi_safe_mask;

	struct srcu_data *sdp;



	if (!IS_ENABLED(CONFIG_PROVE_RCU))

		return;

	/* NMI-unsafe use in NMI is a bad sign */

	WARN_ON_ONCE(!nmi_safe && in_nmi());

	sdp = raw_cpu_ptr(ssp->sda);
@@ -652,6 +651,8 @@ static void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe) 
	}

	WARN_ONCE(old_nmi_safe_mask != nmi_safe_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_nmi_safe_mask, nmi_safe_mask);

}

EXPORT_SYMBOL_GPL(srcu_check_nmi_safety);

#endif /* CONFIG_PROVE_RCU */



/*

 * Counts the new reader in the appropriate per-CPU element of the
@@ -665,7 +666,6 @@ int __srcu_read_lock(struct srcu_struct *ssp) 
	idx = READ_ONCE(ssp->srcu_idx) & 0x1;

	this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);

	smp_mb(); /* B */  /* Avoid leaking the critical section. */

	srcu_check_nmi_safety(ssp, false);

	return idx;

}

EXPORT_SYMBOL_GPL(__srcu_read_lock);
@@ -679,7 +679,6 @@ void __srcu_read_unlock(struct srcu_struct *ssp, int idx) 
{

	smp_mb(); /* C */  /* Avoid leaking the critical section. */

	this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);

	srcu_check_nmi_safety(ssp, false);

}

EXPORT_SYMBOL_GPL(__srcu_read_unlock);
@@ -690,7 +689,7 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock); 
 * srcu_struct, but in an NMI-safe manner using RMW atomics.

 * Returns an index that must be passed to the matching srcu_read_unlock().

 */

int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe)

int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)

{

	int idx;

	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
@@ -698,8 +697,6 @@ int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe) 
	idx = READ_ONCE(ssp->srcu_idx) & 0x1;

	atomic_long_inc(&sdp->srcu_lock_count[idx]);

	smp_mb__after_atomic(); /* B */  /* Avoid leaking the critical section. */

	if (chknmisafe)

		srcu_check_nmi_safety(ssp, true);

	return idx;

}

EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe);
@@ -709,14 +706,12 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe); 
 * element of the srcu_struct.  Note that this may well be a different

 * CPU than that which was incremented by the corresponding srcu_read_lock().

 */

void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx, bool chknmisafe)

void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)

{

	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);



	smp_mb__before_atomic(); /* C */  /* Avoid leaking the critical section. */

	atomic_long_inc(&sdp->srcu_unlock_count[idx]);

	if (chknmisafe)

		srcu_check_nmi_safety(ssp, true);

}

EXPORT_SYMBOL_GPL(__srcu_read_unlock_nmisafe);
@@ -1163,7 +1158,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, 
	 * SRCU read-side critical section so that the grace-period

	 * sequence number cannot wrap around in the meantime.

	 */

	idx = __srcu_read_lock_nmisafe(ssp, false);

	idx = __srcu_read_lock_nmisafe(ssp);

	ss_state = smp_load_acquire(&ssp->srcu_size_state);

	if (ss_state < SRCU_SIZE_WAIT_CALL)

		sdp = per_cpu_ptr(ssp->sda, 0);
@@ -1196,7 +1191,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, 
		srcu_funnel_gp_start(ssp, sdp, s, do_norm);

	else if (needexp)

		srcu_funnel_exp_start(ssp, sdp_mynode, s);

	__srcu_read_unlock_nmisafe(ssp, idx, false);

	__srcu_read_unlock_nmisafe(ssp, idx);

	return s;

}
@@ -1500,13 +1495,13 @@ void srcu_barrier(struct srcu_struct *ssp) 
	/* Initial count prevents reaching zero until all CBs are posted. */

	atomic_set(&ssp->srcu_barrier_cpu_cnt, 1);



	idx = __srcu_read_lock_nmisafe(ssp, false);

	idx = __srcu_read_lock_nmisafe(ssp);

	if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)

		srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0));

	else

		for_each_possible_cpu(cpu)

			srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));

	__srcu_read_unlock_nmisafe(ssp, idx, false);

	__srcu_read_unlock_nmisafe(ssp, idx);



	/* Remove the initial count, at which point reaching zero can happen. */

	if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))