linux-kernel - [PATCH v4 10/14] locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read

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Message-ID: <20220829124719.675715-11-elver@google.com>
Date:   Mon, 29 Aug 2022 14:47:15 +0200
From:   Marco Elver <elver@...gle.com>
To:     elver@...gle.com, Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-perf-users@...r.kernel.org,
        x86@...nel.org, linux-sh@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        Ian Rogers <irogers@...gle.com>
Subject: [PATCH v4 10/14] locking/percpu-rwsem: Add percpu_is_write_locked()
 and percpu_is_read_locked()

Implement simple accessors to probe percpu-rwsem's locked state:
percpu_is_write_locked(), percpu_is_read_locked().

Signed-off-by: Marco Elver <elver@...gle.com>
Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>
Acked-by: Ian Rogers <irogers@...gle.com>
---
v4:
* Due to spurious read_count increments in __percpu_down_read_trylock()
  if sem->block != 0, check that !sem->block (reported by Peter).

v2:
* New patch.
---
 include/linux/percpu-rwsem.h  | 6 ++++++
 kernel/locking/percpu-rwsem.c | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index 5fda40f97fe9..36b942b67b7d 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -121,9 +121,15 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 	preempt_enable();
 }
 
+extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
 extern void percpu_down_write(struct percpu_rw_semaphore *);
 extern void percpu_up_write(struct percpu_rw_semaphore *);
 
+static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
+{
+	return atomic_read(&sem->block);
+}
+
 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
 				const char *, struct lock_class_key *);
 
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 5fe4c5495ba3..185bd1c906b0 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -192,6 +192,12 @@ EXPORT_SYMBOL_GPL(__percpu_down_read);
 	__sum;								\
 })
 
+bool percpu_is_read_locked(struct percpu_rw_semaphore *sem)
+{
+	return per_cpu_sum(*sem->read_count) != 0 && !atomic_read(&sem->block);
+}
+EXPORT_SYMBOL_GPL(percpu_is_read_locked);
+
 /*
  * Return true if the modular sum of the sem->read_count per-CPU variable is
  * zero.  If this sum is zero, then it is stable due to the fact that if any
-- 
2.37.2.672.g94769d06f0-goog