[PATCH RFC rcu 3/4] srcu: Check for consistent per-CPU per-srcu_struct NMI safety

Paul E. McKenney
2022-09-21T14:46:58Z

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: Paul E. McKenney <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
---
include/linux/srcu.h | 4 ++--
include/linux/srcutiny.h | 4 ++--
include/linux/srcutree.h | 9 +++++++--
kernel/rcu/srcutree.c | 38 ++++++++++++++++++++++++++++++++------
4 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index aa9406e88fb8..274d7200ce4e 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -178,7 +178,7 @@ 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);
@@ -223,7 +223,7 @@ 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);
}
diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index 278331bd7766..f890301f123d 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -90,13 +90,13 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
data_race(READ_ONCE(ssp->srcu_idx_max)));
}

-static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp)
+static inline int __srcu_read_lock_nmisafe(struct srcu_struct *ssp, bool chknmisafe)
{
BUG();
return 0;
}

-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)
{
BUG();
}
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index d45dd507f4a5..35ffdedf86cc 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -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.
*/
@@ -154,7 +159,7 @@ void synchronize_srcu_expedited(struct srcu_struct *ssp);
void srcu_barrier(struct srcu_struct *ssp);
void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf);

-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);

#endif
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index f5b1485e79aa..09a11f2c2042 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -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);

@@ -659,7 +681,7 @@ 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);
@@ -667,6 +689,8 @@ 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);
@@ -676,12 +700,14 @@ 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);

@@ -1121,7 +1147,7 @@ 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);
@@ -1154,7 +1180,7 @@ 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;
}

@@ -1458,13 +1484,13 @@ 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))
--
2.31.1.189.g2e36527f23