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Date: Thu, 26 Jun 2014 12:21:17 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Josh Triplett <josh@...htriplett.org>,
Lai Jiangshan <laijs@...fujitsu.com>,
Peter Zijlstra <peterz@...radead.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] rcu: uninline rcu_lock_acquire() and
rcu_lock_release()
On Thu, Jun 26, 2014 at 08:36:57PM +0200, Oleg Nesterov wrote:
> On 06/26, Oleg Nesterov wrote:
> >
> > On 06/26, Oleg Nesterov wrote:
> > >
> > > +static void rcu_release_map(struct lockdep_map *map, unsigned long ip)
> > > +{
> > > + rcu_lockdep_assert_watching();
> > > + __rcu_lock_release(&rcu_lock_map, ip);
> > ^^^^^^^^^^^^
> > OOPS. This should be "map". Please see v2 below.
>
> Argh. Probably you should simply ignore me.
My day has been a bit like that as well. I can only be thankful
for source-code control systems such as git...
> > +static void rcu_release_map(struct lockdep_map *map, unsigned long ip)
> > +{
> > + rcu_lockdep_assert_watching();
> > + __rcu_lock_release(&map, ip);
>
> "map", not "&map". I fixed this before I sent v2, but apparently forgot to
> -add before --amend.
>
> Sorry for noise.
Not a problem! Looks generally sane, but with a bit of adjustment
still needed.
I got some test failures on v2:
o Build breakage if built with CONFIG_DEBUG_LOCK_ALLOC=n. I believe
that the best way to fix this is to #ifdef out the bodies of
__rcu_lock_acquire() and __rcu_lock_release(), but maybe you
have something else in mind.
o Lockdep splat as follows, which might well be due to the
"&map" that you noted above:
[ 0.000000] =====================================
[ 0.000000] [ BUG: bad unlock balance detected! ]
[ 0.000000] 3.16.0-rc1+ #1 Not tainted
[ 0.000000] -------------------------------------
[ 0.000000] swapper/0 is trying to release lock (X?à<81>ÿÿÿÿ<97>^Sò<81>ÿÿÿÿX?à<81>ÿÿÿÿ{±ò<81>@B^O) at:
[ 0.000000] [<ffffffff8107cb61>] init_idle+0xc1/0x150
[ 0.000000] but there are no more locks to release!
And a few other things noted below.
Thanx, Paul
> -------------------------------------------------------------------------------
> Subject: [PATCH v3 1/1] rcu: uninline rcu_lock_acquire() and rcu_lock_release()
>
> Uninline rcu_lock_acquire() and rcu_lock_release() to shrink .text/data.
> The difference in "size vmlinux" looks good,
>
> with CONFIG_DEBUG_LOCK_ALLOC
>
> - 5377829 3018320 14757888 23154037
> + 5352229 3010160 14757888 23120277
>
> 33760 bytes saved.
>
> with CONFIG_DEBUG_LOCK_ALLOC + CONFIG_PROVE_RCU + CONFIG_TREE_RCU_TRACE
>
> - 5682283 3022936 14757888 23463107
> + 5578667 3026776 14757888 23363331
>
> saves 99776 bytes.
Nice savings!
> However, this obviously means that the "warn once" logic is moved from
> the current callers of rcu_lockdep_assert(rcu_is_watching()) to update.c.
Which should be fine.
> Also, with this patch we do not bother to report which function abused
> rcu_is_watching(), this should be clear from dump_stack().
Which also should be fine. I was going to suggest a macro wrapper, but
that would of course bloat the kernel with the function names...
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
> include/linux/rcupdate.h | 55 ++++++++++++++++++++++---------------------
> include/linux/srcu.h | 4 +-
> kernel/rcu/rcu.h | 6 ++--
> kernel/rcu/update.c | 57 ++++++++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 90 insertions(+), 32 deletions(-)
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 5a75d19..a5b1631 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -379,18 +379,34 @@ static inline bool rcu_lockdep_current_cpu_online(void)
> }
> #endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
>
> -#ifdef CONFIG_DEBUG_LOCK_ALLOC
> -
> -static inline void rcu_lock_acquire(struct lockdep_map *map)
> +static inline void __rcu_lock_acquire(struct lockdep_map *map, unsigned long ip)
> {
> - lock_acquire(map, 0, 0, 2, 0, NULL, _THIS_IP_);
> + lock_acquire(map, 0, 0, 2, 0, NULL, ip);
I believe that the above line of code needs to be under #ifdef
CONFIG_DEBUG_LOCK_ALLOC, otherwise we get build failures due to
accesses to #ifdefed-out structure members and variables.
> }
>
> -static inline void rcu_lock_release(struct lockdep_map *map)
> +static inline void __rcu_lock_release(struct lockdep_map *map, unsigned long ip)
> {
> - lock_release(map, 1, _THIS_IP_);
> + lock_release(map, 1, ip);
Ditto.
> }
>
> +#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_PROVE_RCU)
"#ifdef CONFIG_DEBUG_LOCK_ALLOC" should suffice here. If CONFIG_PROVE_RCU
is set, then CONFIG_DEBUG_LOCK_ALLOC is guaranteed to also be set.
> +extern void rcu_lock_acquire(void);
> +extern void rcu_lock_release(void);
> +extern void rcu_lock_acquire_bh(void);
> +extern void rcu_lock_release_bh(void);
> +extern void rcu_lock_acquire_sched(void);
> +extern void rcu_lock_release_sched(void);
> +#else
> +#define rcu_lock_acquire() do { } while (0)
> +#define rcu_lock_release() do { } while (0)
> +#define rcu_lock_acquire_bh() do { } while (0)
> +#define rcu_lock_release_bh() do { } while (0)
> +#define rcu_lock_acquire_sched() do { } while (0)
> +#define rcu_lock_release_sched() do { } while (0)
> +#endif
> +
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +
> extern struct lockdep_map rcu_lock_map;
> extern struct lockdep_map rcu_bh_lock_map;
> extern struct lockdep_map rcu_sched_lock_map;
> @@ -489,9 +505,6 @@ static inline int rcu_read_lock_sched_held(void)
>
> #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>
> -# define rcu_lock_acquire(a) do { } while (0)
> -# define rcu_lock_release(a) do { } while (0)
> -
> static inline int rcu_read_lock_held(void)
> {
> return 1;
> @@ -866,9 +879,7 @@ static inline void rcu_read_lock(void)
> {
> __rcu_read_lock();
> __acquire(RCU);
> - rcu_lock_acquire(&rcu_lock_map);
> - rcu_lockdep_assert(rcu_is_watching(),
> - "rcu_read_lock() used illegally while idle");
> + rcu_lock_acquire();
> }
>
> /*
> @@ -888,9 +899,7 @@ static inline void rcu_read_lock(void)
> */
> static inline void rcu_read_unlock(void)
> {
> - rcu_lockdep_assert(rcu_is_watching(),
> - "rcu_read_unlock() used illegally while idle");
> - rcu_lock_release(&rcu_lock_map);
> + rcu_lock_release();
> __release(RCU);
> __rcu_read_unlock();
> }
> @@ -916,9 +925,7 @@ static inline void rcu_read_lock_bh(void)
> {
> local_bh_disable();
> __acquire(RCU_BH);
> - rcu_lock_acquire(&rcu_bh_lock_map);
> - rcu_lockdep_assert(rcu_is_watching(),
> - "rcu_read_lock_bh() used illegally while idle");
> + rcu_lock_acquire_bh();
> }
>
> /*
> @@ -928,9 +935,7 @@ static inline void rcu_read_lock_bh(void)
> */
> static inline void rcu_read_unlock_bh(void)
> {
> - rcu_lockdep_assert(rcu_is_watching(),
> - "rcu_read_unlock_bh() used illegally while idle");
> - rcu_lock_release(&rcu_bh_lock_map);
> + rcu_lock_release_bh();
> __release(RCU_BH);
> local_bh_enable();
> }
> @@ -952,9 +957,7 @@ static inline void rcu_read_lock_sched(void)
> {
> preempt_disable();
> __acquire(RCU_SCHED);
> - rcu_lock_acquire(&rcu_sched_lock_map);
> - rcu_lockdep_assert(rcu_is_watching(),
> - "rcu_read_lock_sched() used illegally while idle");
> + rcu_lock_acquire_sched();
> }
>
> /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
> @@ -971,9 +974,7 @@ static inline notrace void rcu_read_lock_sched_notrace(void)
> */
> static inline void rcu_read_unlock_sched(void)
> {
> - rcu_lockdep_assert(rcu_is_watching(),
> - "rcu_read_unlock_sched() used illegally while idle");
> - rcu_lock_release(&rcu_sched_lock_map);
> + rcu_lock_release_sched();
> __release(RCU_SCHED);
> preempt_enable();
> }
> diff --git a/include/linux/srcu.h b/include/linux/srcu.h
> index a2783cb..5c06289 100644
> --- a/include/linux/srcu.h
> +++ b/include/linux/srcu.h
> @@ -219,7 +219,7 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
> {
> int retval = __srcu_read_lock(sp);
>
> - rcu_lock_acquire(&(sp)->dep_map);
> + __rcu_lock_acquire(&(sp)->dep_map, _THIS_IP_);
> return retval;
> }
>
> @@ -233,7 +233,7 @@ static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
> static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
> __releases(sp)
> {
> - rcu_lock_release(&(sp)->dep_map);
> + __rcu_lock_release(&(sp)->dep_map, _THIS_IP_);
> __srcu_read_unlock(sp, idx);
> }
>
> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> index bfda272..5702910 100644
> --- a/kernel/rcu/rcu.h
> +++ b/kernel/rcu/rcu.h
> @@ -103,16 +103,16 @@ static inline bool __rcu_reclaim(const char *rn, struct rcu_head *head)
> {
> unsigned long offset = (unsigned long)head->func;
>
> - rcu_lock_acquire(&rcu_callback_map);
> + __rcu_lock_acquire(&rcu_callback_map, _THIS_IP_);
> if (__is_kfree_rcu_offset(offset)) {
> RCU_TRACE(trace_rcu_invoke_kfree_callback(rn, head, offset));
> kfree((void *)head - offset);
> - rcu_lock_release(&rcu_callback_map);
> + __rcu_lock_release(&rcu_callback_map, _THIS_IP_);
> return 1;
Commit 08c11a77e8 in my -rcu tree chose a particularly bad time to
change this to "true" and the "0" below to "false". Could you
please rebase on top of that commit? (Easy enough for me to
hand-edit the patch, but the way today is going, I will probably
mess it up.)
> } else {
> RCU_TRACE(trace_rcu_invoke_callback(rn, head));
> head->func(head);
> - rcu_lock_release(&rcu_callback_map);
> + __rcu_lock_release(&rcu_callback_map, _THIS_IP_);
> return 0;
> }
> }
> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> index a2aeb4d..9cbdf52 100644
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -168,6 +168,63 @@ EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
>
> #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
>
> +#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_PROVE_RCU)
> +
> +static void rcu_lockdep_assert_watching(void)
> +{
> + rcu_lockdep_assert(rcu_is_watching(), "RCU used illegally while idle");
> +}
> +
> +static void rcu_acquire_map(struct lockdep_map *map, unsigned long ip)
> +{
> + __rcu_lock_acquire(map, ip);
> + rcu_lockdep_assert_watching();
> +}
> +
> +static void rcu_release_map(struct lockdep_map *map, unsigned long ip)
> +{
> + rcu_lockdep_assert_watching();
> + __rcu_lock_release(map, ip);
> +}
> +
> +void rcu_lock_acquire(void)
> +{
> + rcu_acquire_map(&rcu_lock_map, _RET_IP_);
> +}
> +EXPORT_SYMBOL(rcu_lock_acquire);
> +
> +void rcu_lock_release(void)
> +{
> + rcu_release_map(&rcu_lock_map, _RET_IP_);
> +}
> +EXPORT_SYMBOL(rcu_lock_release);
> +
> +void rcu_lock_acquire_bh(void)
> +{
> + rcu_acquire_map(&rcu_bh_lock_map, _RET_IP_);
> +}
> +EXPORT_SYMBOL(rcu_lock_acquire_bh);
> +
> +void rcu_lock_release_bh(void)
> +{
> + rcu_release_map(&rcu_bh_lock_map, _RET_IP_);
> +}
> +EXPORT_SYMBOL(rcu_lock_release_bh);
> +
> +void rcu_lock_acquire_sched(void)
> +{
> + rcu_acquire_map(&rcu_sched_lock_map, _RET_IP_);
> +}
> +EXPORT_SYMBOL(rcu_lock_acquire_sched);
> +
> +void rcu_lock_release_sched(void)
> +{
> + rcu_release_map(&rcu_sched_lock_map, _RET_IP_);
> +}
> +EXPORT_SYMBOL(rcu_lock_release_sched);
> +
> +#endif
> +
> struct rcu_synchronize {
> struct rcu_head head;
> struct completion completion;
> --
> 1.5.5.1
>
>
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