linux-kernel - [PATCH 2/3] rwsem: Implement down_read

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Message-ID: <87k0tybqfy.fsf@x220.int.ebiederm.org>
Date:   Thu, 03 Dec 2020 14:11:13 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Vasiliy Kulikov <segoon@...nwall.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Bernd Edlinger <bernd.edlinger@...mail.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Christopher Yeoh <cyeoh@....ibm.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Arnd Bergmann <arnd@...db.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: [PATCH 2/3] rwsem: Implement down_read_interruptible


In preparation for converting exec_update_mutex to a rwsem so that
multiple readers can execute in parallel and not deadlock, add
down_read_interruptible.  This is needed for perf_event_open to be
converted (with no semantic changes) from working on a mutex to
wroking on a rwsem.

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Will Deacon <will@...nel.org>
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
---
 include/linux/rwsem.h  |  1 +
 kernel/locking/rwsem.c | 26 ++++++++++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
index 13021b08b2ed..4c715be48717 100644
--- a/include/linux/rwsem.h
+++ b/include/linux/rwsem.h
@@ -123,6 +123,7 @@ static inline int rwsem_is_contended(struct rw_semaphore *sem)
  * lock for reading
  */
 extern void down_read(struct rw_semaphore *sem);
+extern int __must_check down_read_interruptible(struct rw_semaphore *sem);
 extern int __must_check down_read_killable(struct rw_semaphore *sem);
 
 /*
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 54d11cb97551..a163542d178e 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1345,6 +1345,18 @@ static inline void __down_read(struct rw_semaphore *sem)
 	}
 }
 
+static inline int __down_read_interruptible(struct rw_semaphore *sem)
+{
+	if (!rwsem_read_trylock(sem)) {
+		if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_INTERRUPTIBLE)))
+			return -EINTR;
+		DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
+	} else {
+		rwsem_set_reader_owned(sem);
+	}
+	return 0;
+}
+
 static inline int __down_read_killable(struct rw_semaphore *sem)
 {
 	if (!rwsem_read_trylock(sem)) {
@@ -1495,6 +1507,20 @@ void __sched down_read(struct rw_semaphore *sem)
 }
 EXPORT_SYMBOL(down_read);
 
+int __sched down_read_interruptible(struct rw_semaphore *sem)
+{
+	might_sleep();
+	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
+
+	if (LOCK_CONTENDED_RETURN(sem, __down_read_trylock, __down_read_interruptible)) {
+		rwsem_release(&sem->dep_map, _RET_IP_);
+		return -EINTR;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(down_read_interruptible);
+
 int __sched down_read_killable(struct rw_semaphore *sem)
 {
 	might_sleep();
-- 
2.25.0