Re: [PATCH] srcu: Export srcu_check_nmi_safety() to modules

From: Paul E. McKenney
Date: Tue Oct 18 2022 - 13:50:45 EST

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On Tue, Oct 18, 2022 at 12:45:33PM +0200, Frederic Weisbecker wrote:
> On Tue, Oct 18, 2022 at 09:39:06AM +0800, Zqiang wrote:
> > When enable CONFIG_PROVE_RCU and built modules, the following
> > error appear:
> >
> > ERROR: modpost: "srcu_check_nmi_safety" [kernel/rcu/rcutorture.ko] undefined!
> > ERROR: modpost: "srcu_check_nmi_safety" [kernel/rcu/rcuscale.ko] undefined!
> >
> > This commit fix it by exporting the srcu_check_nmi_safety().
> >
> > Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
>
> Paul, whichever way you prefer, editing the commit or adding this
> one on top.
>
> Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>

Thank you all!

This is what I currently have, folded into Frederic's original.

Thoughts?

Thanx, Paul

------------------------------------------------------------------------

commit 88a6ff77b433f1f60af01fc94430eaad448ca491
Author: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date: Thu Oct 13 19:22:44 2022 +0200

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: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 565f60d574847..f0814ffca34bb 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -52,8 +52,6 @@ int init_srcu_struct(struct srcu_struct *ssp);
#else
/* Dummy definition for things like notifiers. Actual use gets link error. */
struct srcu_struct { };
-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

void call_srcu(struct srcu_struct *ssp, struct rcu_head *head,
@@ -66,6 +64,20 @@ unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp);
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);
+#else
+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)
+{
+ __srcu_read_unlock(ssp, idx);
+}
+#endif /* CONFIG_NEED_SRCU_NMI_SAFE */
+
#ifdef CONFIG_SRCU
void srcu_init(void);
#else /* #ifdef CONFIG_SRCU */
@@ -106,6 +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
@@ -163,6 +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;
@@ -179,10 +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;
}
@@ -193,6 +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;
}
@@ -208,6 +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);
}
@@ -223,17 +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);
}

diff --git a/include/linux/srcutiny.h b/include/linux/srcutiny.h
index efd808a23f8d8..a2f620f8c5592 100644
--- a/include/linux/srcutiny.h
+++ b/include/linux/srcutiny.h
@@ -87,16 +87,4 @@ static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])));
}
-
-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, bool chknmisafe)
-{
- BUG();
-}
-
#endif
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index 35ffdedf86ccb..c689a81752c9a 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -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.
*/
@@ -159,7 +155,4 @@ 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, 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 272830a87e566..ca4b5dcec675b 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -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))

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