linux-kernel - Re: [PATCH v2 7/9] locking/rwlocks: introduce write_lock

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Message-ID: <YZfrMTAXV56HFWJY@google.com>
Date:   Fri, 19 Nov 2021 10:21:37 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 7/9] locking/rwlocks: introduce write_lock_nested

On Fri, Nov 19, 2021 at 11:35:16AM +0100, Sebastian Andrzej Siewior wrote:
> On 2021-11-15 10:59:07 [-0800], Minchan Kim wrote:
> > diff --git a/include/linux/rwlock_rt.h b/include/linux/rwlock_rt.h
> > index 49c1f3842ed5..efd6da62c893 100644
> > --- a/include/linux/rwlock_rt.h
> > +++ b/include/linux/rwlock_rt.h
> > @@ -28,6 +28,7 @@ extern void rt_read_lock(rwlock_t *rwlock);
> >  extern int rt_read_trylock(rwlock_t *rwlock);
> >  extern void rt_read_unlock(rwlock_t *rwlock);
> >  extern void rt_write_lock(rwlock_t *rwlock);
> > +extern void rt_write_lock_nested(rwlock_t *rwlock, int subclass);
> >  extern int rt_write_trylock(rwlock_t *rwlock);
> >  extern void rt_write_unlock(rwlock_t *rwlock);
> >
> > @@ -83,6 +84,11 @@ static __always_inline void write_lock(rwlock_t *rwlock)
> >  	rt_write_lock(rwlock);
> >  }
> >  
> > +static __always_inline void write_lock_nested(rwlock_t *rwlock, int subclass)
> > +{
> > +	rt_write_lock_nested(rwlock, subclass);
> > +}
> > +
> 
> These two hunks as-is don't work. You need a CONFIG_DEBUG_LOCK_ALLOC block and
> in the !CONFIG_DEBUG_LOCK_ALLOC case you need
> 
> #define rt_write_lock_nested(lock, subclass)     rt_write_lock(((void)(subclass), (lock)))

Guess you meant #define write_lock_nested.

> 
> >  static __always_inline void write_lock_bh(rwlock_t *rwlock)
> >  {
> >  	local_bh_disable();
> > diff --git a/kernel/locking/spinlock_rt.c b/kernel/locking/spinlock_rt.c
> > index b2e553f9255b..b82d346f1e00 100644
> > --- a/kernel/locking/spinlock_rt.c
> > +++ b/kernel/locking/spinlock_rt.c
> > @@ -239,6 +239,18 @@ void __sched rt_write_lock(rwlock_t *rwlock)
> >  }
> >  EXPORT_SYMBOL(rt_write_lock);
> >  
> > +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> > +void __sched rt_write_lock_nested(rwlock_t *rwlock, int subclass)
> > +{
> > +	___might_sleep(__FILE__, __LINE__, 0);
> 
> This _must_ be rtlock_might_resched() like it is done in rt_write_lock()
> above.

I should have Cced you. Thanks for the catch.
If it's fine, Andrew, could you fold it?

Thank you.

>From 81f8721bc76d5f8c94770e53c6ad2e41aec8ab21 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@...nel.org>
Date: Fri, 19 Nov 2021 10:15:00 -0800
Subject: [PATCH] locking/rwlocks: fix write_lock_nested for RT

Fix build break of write_lock_nested for RT.

Suggested-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 include/linux/rwlock_rt.h    | 4 ++++
 kernel/locking/spinlock_rt.c | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/rwlock_rt.h b/include/linux/rwlock_rt.h
index efd6da62c893..8544ff05e594 100644
--- a/include/linux/rwlock_rt.h
+++ b/include/linux/rwlock_rt.h
@@ -84,10 +84,14 @@ static __always_inline void write_lock(rwlock_t *rwlock)
 	rt_write_lock(rwlock);
 }
 
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
 static __always_inline void write_lock_nested(rwlock_t *rwlock, int subclass)
 {
 	rt_write_lock_nested(rwlock, subclass);
 }
+#else
+#define write_lock_nested(lock, subclass)	rt_write_lock(((void)(subclass), (lock)))
+#endif
 
 static __always_inline void write_lock_bh(rwlock_t *rwlock)
 {
diff --git a/kernel/locking/spinlock_rt.c b/kernel/locking/spinlock_rt.c
index b82d346f1e00..b501aef820d5 100644
--- a/kernel/locking/spinlock_rt.c
+++ b/kernel/locking/spinlock_rt.c
@@ -242,7 +242,7 @@ EXPORT_SYMBOL(rt_write_lock);
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 void __sched rt_write_lock_nested(rwlock_t *rwlock, int subclass)
 {
-	___might_sleep(__FILE__, __LINE__, 0);
+	rtlock_might_resched();
 	rwlock_acquire(&rwlock->dep_map, subclass, 0, _RET_IP_);
 	rwbase_write_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
 	rcu_read_lock();
-- 
2.34.0.rc2.393.gf8c9666880-goog