Commit 27120e7d authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

srcu: Check for consistent per-CPU per-srcu_struct NMI safety 

This commit adds runtime checks to verify that a given srcu_struct uses
consistent NMI-safe (or not) read-side primitives on a per-CPU basis.

Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/



Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
parent 2e83b879

include/linux/srcu.h

+6 −6
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) __acquires(ssp);

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

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);

#else

static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)

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

{

	return __srcu_read_lock(ssp);

}

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

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

{

	__srcu_read_unlock(ssp, idx);

}
@@ -192,7 +192,7 @@ 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);

		retval = __srcu_read_lock_nmisafe(ssp, true);

	else

		retval = __srcu_read_lock(ssp);

	rcu_lock_acquire(&(ssp)->dep_map);
@@ -237,7 +237,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) 
	WARN_ON_ONCE(idx & ~0x1);

	rcu_lock_release(&(ssp)->dep_map);

	if (IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE))

		__srcu_read_unlock_nmisafe(ssp, idx);

		__srcu_read_unlock_nmisafe(ssp, idx, true);

	else

		__srcu_read_unlock(ssp, idx);

}

include/linux/srcutree.h

+5 −0
Original line number Diff line number Diff line
@@ -25,6 +25,7 @@ struct srcu_data { 
	/* Read-side state. */

	atomic_long_t srcu_lock_count[2];	/* Locks per CPU. */

	atomic_long_t srcu_unlock_count[2];	/* Unlocks per CPU. */

	int srcu_nmi_safety;			/* NMI-safe srcu_struct structure? */



	/* Update-side state. */

	spinlock_t __private lock ____cacheline_internodealigned_in_smp;
@@ -42,6 +43,10 @@ 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

+32 −6
Original line number Diff line number Diff line
@@ -626,6 +626,26 @@ void cleanup_srcu_struct(struct srcu_struct *ssp) 
}

EXPORT_SYMBOL_GPL(cleanup_srcu_struct);



/*

 * Check for consistent NMI safety.

 */

static 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;

	sdp = raw_cpu_ptr(ssp->sda);

	old_nmi_safe_mask = READ_ONCE(sdp->srcu_nmi_safety);

	if (!old_nmi_safe_mask) {

		WRITE_ONCE(sdp->srcu_nmi_safety, nmi_safe_mask);

		return;

	}

	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);

}



/*

 * Counts the new reader in the appropriate per-CPU element of the

 * srcu_struct.
@@ -638,6 +658,7 @@ 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);
@@ -651,6 +672,7 @@ 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);
@@ -661,7 +683,7 @@ 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)

int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe)

{

	int idx;

	struct srcu_data *sdp = raw_cpu_ptr(ssp->sda);
@@ -669,6 +691,8 @@ int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) 
	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);
@@ -678,12 +702,14 @@ 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)

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

{

	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);
@@ -1125,7 +1151,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, 
	int ss_state;



	check_init_srcu_struct(ssp);

	idx = __srcu_read_lock_nmisafe(ssp);

	idx = __srcu_read_lock_nmisafe(ssp, false);

	ss_state = smp_load_acquire(&ssp->srcu_size_state);

	if (ss_state < SRCU_SIZE_WAIT_CALL)

		sdp = per_cpu_ptr(ssp->sda, 0);
@@ -1158,7 +1184,7 @@ 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);

	__srcu_read_unlock_nmisafe(ssp, idx, false);

	return s;

}
@@ -1462,13 +1488,13 @@ 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);

	idx = __srcu_read_lock_nmisafe(ssp, false);

	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);

	__srcu_read_unlock_nmisafe(ssp, idx, false);



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

	if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))