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Message-Id: <20240903163318.480678-6-paulmck@kernel.org>
Date: Tue, 3 Sep 2024 09:33:13 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
kernel-team@...a.com,
rostedt@...dmis.org,
Alexei Starovoitov <ast@...nel.org>,
Andrii Nakryiko <andrii@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Kent Overstreet <kent.overstreet@...ux.dev>,
bpf@...r.kernel.org,
"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 06/11] srcu: Convert srcu_data ->srcu_reader_flavor to bit field
This commit adds SRCU_READ_FLAVOR_NORMAL and SRCU_READ_FLAVOR_NMI bit
definitions and uses them in preparation for adding a third SRCU reader
flavor.
While in the area, improve a few comments.
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>
Cc: <bpf@...r.kernel.org>
---
include/linux/srcu.h | 35 +++++++++++++++++++----------------
include/linux/srcutree.h | 4 ++++
kernel/rcu/srcutree.c | 22 +++++++++++-----------
3 files changed, 34 insertions(+), 27 deletions(-)
diff --git a/include/linux/srcu.h b/include/linux/srcu.h
index 06728ef6f32a4..84daaa33ea0ab 100644
--- a/include/linux/srcu.h
+++ b/include/linux/srcu.h
@@ -176,10 +176,6 @@ 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_read_flavor(struct srcu_struct *ssp, int read_flavor);
#else
@@ -235,16 +231,19 @@ static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flav
* a mutex that is held elsewhere while calling synchronize_srcu() or
* synchronize_srcu_expedited().
*
- * Note that srcu_read_lock() and the matching srcu_read_unlock() must
- * occur in the same context, for example, it is illegal to invoke
- * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
- * was invoked in process context.
+ * The return value from srcu_read_lock() must be passed unaltered
+ * to the matching srcu_read_unlock(). Note that srcu_read_lock() and
+ * the matching srcu_read_unlock() must occur in the same context, for
+ * example, it is illegal to invoke srcu_read_unlock() in an irq handler
+ * if the matching srcu_read_lock() was invoked in process context. Or,
+ * for that matter to invoke srcu_read_unlock() from one task and the
+ * matching srcu_read_lock() from another.
*/
static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
{
int retval;
- srcu_check_read_flavor(ssp, false);
+ srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
retval = __srcu_read_lock(ssp);
srcu_lock_acquire(&ssp->dep_map);
return retval;
@@ -256,12 +255,16 @@ static inline int srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp)
*
* Enter an SRCU read-side critical section, but in an NMI-safe manner.
* See srcu_read_lock() for more information.
+ *
+ * If srcu_read_lock_nmisafe() is ever used on an srcu_struct structure,
+ * then none of the other flavors may be used, whether before, during,
+ * or after.
*/
static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp)
{
int retval;
- srcu_check_read_flavor(ssp, true);
+ srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
retval = __srcu_read_lock_nmisafe(ssp);
rcu_try_lock_acquire(&ssp->dep_map);
return retval;
@@ -273,7 +276,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
{
int retval;
- srcu_check_read_flavor(ssp, false);
+ srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
retval = __srcu_read_lock(ssp);
return retval;
}
@@ -302,7 +305,7 @@ srcu_read_lock_notrace(struct srcu_struct *ssp) __acquires(ssp)
static inline int srcu_down_read(struct srcu_struct *ssp) __acquires(ssp)
{
WARN_ON_ONCE(in_nmi());
- srcu_check_read_flavor(ssp, false);
+ srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
return __srcu_read_lock(ssp);
}
@@ -317,7 +320,7 @@ static inline void srcu_read_unlock(struct srcu_struct *ssp, int idx)
__releases(ssp)
{
WARN_ON_ONCE(idx & ~0x1);
- srcu_check_read_flavor(ssp, false);
+ srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
srcu_lock_release(&ssp->dep_map);
__srcu_read_unlock(ssp, idx);
}
@@ -333,7 +336,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
__releases(ssp)
{
WARN_ON_ONCE(idx & ~0x1);
- srcu_check_read_flavor(ssp, true);
+ srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NMI);
rcu_lock_release(&ssp->dep_map);
__srcu_read_unlock_nmisafe(ssp, idx);
}
@@ -342,7 +345,7 @@ static inline void srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx)
static inline notrace void
srcu_read_unlock_notrace(struct srcu_struct *ssp, int idx) __releases(ssp)
{
- srcu_check_read_flavor(ssp, false);
+ srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
__srcu_read_unlock(ssp, idx);
}
@@ -359,7 +362,7 @@ static inline void srcu_up_read(struct srcu_struct *ssp, int idx)
{
WARN_ON_ONCE(idx & ~0x1);
WARN_ON_ONCE(in_nmi());
- srcu_check_read_flavor(ssp, false);
+ srcu_check_read_flavor(ssp, SRCU_READ_FLAVOR_NORMAL);
__srcu_read_unlock(ssp, idx);
}
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h
index ab7d8d215b84b..79ad809c7f035 100644
--- a/include/linux/srcutree.h
+++ b/include/linux/srcutree.h
@@ -43,6 +43,10 @@ struct srcu_data {
struct srcu_struct *ssp;
};
+/* Values for ->srcu_reader_flavor. */
+#define SRCU_READ_FLAVOR_NORMAL 0x1 // srcu_read_lock().
+#define SRCU_READ_FLAVOR_NMI 0x2 // srcu_read_lock_nmisafe().
+
/*
* Node in SRCU combining tree, similar in function to rcu_data.
*/
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 54ca2ea2b7d68..602b4b8c4b891 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -463,7 +463,7 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx)
mask = mask | READ_ONCE(sdp->srcu_reader_flavor);
}
WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask - 1)),
- "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp);
+ "Mixed reader flavors for srcu_struct at %ps.\n", ssp);
return sum;
}
@@ -703,21 +703,21 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
*/
void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor)
{
- int reader_flavor_mask = 1 << read_flavor;
- int old_reader_flavor_mask;
+ int old_read_flavor;
struct srcu_data *sdp;
- /* NMI-unsafe use in NMI is a bad sign */
- WARN_ON_ONCE(!read_flavor && in_nmi());
+ /* NMI-unsafe use in NMI is a bad sign, as is multi-bit read_flavor values. */
+ WARN_ON_ONCE((read_flavor != SRCU_READ_FLAVOR_NMI) && in_nmi());
+ WARN_ON_ONCE(read_flavor & (read_flavor - 1));
+
sdp = raw_cpu_ptr(ssp->sda);
- old_reader_flavor_mask = READ_ONCE(sdp->srcu_reader_flavor);
- if (!old_reader_flavor_mask) {
- old_reader_flavor_mask = cmpxchg(&sdp->srcu_reader_flavor, 0, reader_flavor_mask);
- if (!old_reader_flavor_mask) {
+ old_read_flavor = READ_ONCE(sdp->srcu_reader_flavor);
+ if (!old_read_flavor) {
+ old_read_flavor = cmpxchg(&sdp->srcu_reader_flavor, 0, read_flavor);
+ if (!old_read_flavor)
return;
- }
}
- WARN_ONCE(old_reader_flavor_mask != reader_flavor_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_reader_flavor_mask, reader_flavor_mask);
+ WARN_ONCE(old_read_flavor != read_flavor, "CPU %d old state %d new state %d\n", sdp->cpu, old_read_flavor, read_flavor);
}
EXPORT_SYMBOL_GPL(srcu_check_read_flavor);
#endif /* CONFIG_PROVE_RCU */
--
2.40.1
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