Re: [PATCH v2] rt_spin_lock: To list the correct owner of rt_spin_lock

[Steven Rostedt]

On Mon, 27 Jun 2022 21:41:38 +0530
Mintu Patel <mintupatel89@xxxxxxxxx> wrote:

Hi Mintu,

FYI, a v2 should never be a reply to the v1. It should always start its own
thread, otherwise tooling and such will miss it.

>    rt_spin_lock is actually mutex on RT Kernel so it goes for contention
>    for lock. Currently owners of rt_spin_lock are decided before actual
>    acquiring of lock. This patch would depict the correct owner of
>    rt_spin_lock. The patch would help in solving crashes and deadlock
>    due to race condition of lock
> 
> acquiring rt_spin_lock        acquired the lock       released the lock
>                     <-------->                <------->
>                     contention period         Held period
> 
> Thread1                             Thread2
> _try_to_take_rt_mutex+0x95c+0x74    enqueue_task_dl+0x8cc/0x8dc
> rt_spin_lock_slowlock_locked+0xac+2 rt_mutex_setprio+0x28c/0x574
> rt_spin_lock_slowlock+0x5c/0x90     task_blocks_rt_mutex+0x240/0x310
> rt_spin_lock+0x58/0x5c              rt_spin_lock_slowlock_locked+0xac/0x2
> driverA_acquire_lock+0x28/0x56      rt_spin_lock_slowlock+0x5c/0x90
> 				    rt_spin_lock+0x58/0x5c
>                                     driverB_acquire_lock+0x48/0x6c
> 
> As per above call traces sample, Thread1 acquired the rt_spin_lock and
> went to critical section on the other hand Thread2 kept trying to acquire
> the same rt_spin_lock held by Thread1 ie contention period is too high.
> Finally Thread2 entered to dl queue due to high held time of the lock by
> Thread1. The below patch would help us to know the correct owner of
> rt_spin_lock and point us the driver's critical section. Respective
> driver need to be debugged for longer held period of lock.
> 
>    ex: cat /sys/kernel/debug/tracing/trace
> 
>    kworker/u13:0-150   [003] .....11   202.761025: rt_spinlock_acquire:
> Process: kworker/u13:0 is acquiring lock: &kbdev->hwaccess_lock
>    kworker/u13:0-150   [003] .....11   202.761039: rt_spinlock_acquired:
> Process: kworker/u13:0 has acquired lock: &kbdev->hwaccess_lock
>    kworker/u13:0-150   [003] .....11   202.761042: rt_spinlock_released:
> Process: kworker/u13:0 has released lock: &kbdev->hwaccess_lock
> 
> Signed-off-by: Mintu Patel <mintupatel89@xxxxxxxxx>
> Signed-off-by: Chinmoy Ghosh <chinmoyghosh2001@xxxxxxxxx>
> Signed-off-by: Vishal Badole <badolevishal1116@xxxxxxxxx>
> Signed-off-by: Vimal Kumar <vimal.kumar32@xxxxxxxxx>
> ---
>  include/trace/events/lock.h     | 38 +++++++++++++++++++++++++++++++++
>  kernel/locking/rtmutex.c        |  4 ++++
>  kernel/locking/rtmutex_common.h | 14 ++++++++++++
>  3 files changed, 56 insertions(+)
> 
> diff --git a/include/trace/events/lock.h b/include/trace/events/lock.h
> index d7512129a324..0564474341c8 100644
> --- a/include/trace/events/lock.h
> +++ b/include/trace/events/lock.h
> @@ -36,6 +36,44 @@ TRACE_EVENT(lock_acquire,
>  		  __get_str(name))
>  );
>  
> +DECLARE_EVENT_CLASS(rt_lock_class,
> +
> +	TP_PROTO(struct lockdep_map *lock, struct task_struct *pname),
> +
> +	TP_ARGS(lock, pname),
> +
> +	TP_STRUCT__entry(
> +		__string(name, lock->name)
> +		__string(process_name, pname->comm)
> +	),
> +
> +	TP_fast_assign(
> +		__assign_str(name, lock->name);
> +		__assign_str(process_name, pname->comm);
> +	),
> +
> +	TP_printk("Process: %s is acquiring lock: %s", __get_str(process_name),
> +		__get_str(name))
> +);
> +
> +DEFINE_EVENT(rt_lock_class, rt_spinlock_acquire,
> +	TP_PROTO(struct lockdep_map *lock, struct task_struct *pname),
> +	TP_ARGS(lock, pname));
> +
> +DEFINE_EVENT_PRINT(rt_lock_class, rt_spinlock_acquired,
> +	TP_PROTO(struct lockdep_map *lock, struct task_struct *pname),
> +	TP_ARGS(lock, pname),
> +	TP_printk("Process: %s has acquired lock: %s", __get_str(process_name),
> +		__get_str(name))
> +	);
> +
> +DEFINE_EVENT_PRINT(rt_lock_class, rt_spinlock_released,
> +	TP_PROTO(struct lockdep_map *lock, struct task_struct *pname),
> +	TP_ARGS(lock, pname),
> +	TP_printk("Process: %s has released lock: %s", __get_str(process_name),
> +		__get_str(name))
> +	);
> +
>  DECLARE_EVENT_CLASS(lock,
>  
>  	TP_PROTO(struct lockdep_map *lock, unsigned long ip),
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 602eb7821a1b..80ba2c0d7923 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -26,6 +26,7 @@
>  #include <linux/timer.h>
>  #include <linux/ww_mutex.h>
>  #include <linux/blkdev.h>
> +#include <trace/events/lock.h>
>  
>  #include "rtmutex_common.h"
>  
> @@ -1144,7 +1145,9 @@ void __lockfunc rt_spin_lock(spinlock_t *lock)
>  	rcu_read_lock();
>  	migrate_disable();
>  	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
> +	do_trace_rt_spinlock_acquire(lock, current);
>  	rt_spin_lock_fastlock(&lock->lock, rt_spin_lock_slowlock);
> +	do_trace_rt_spinlock_acquired(lock, current);
>  }
>  EXPORT_SYMBOL(rt_spin_lock);
>  
> @@ -1169,6 +1172,7 @@ void __lockfunc rt_spin_unlock(spinlock_t *lock)
>  {
>  	/* NOTE: we always pass in '1' for nested, for simplicity */
>  	spin_release(&lock->dep_map, 1, _RET_IP_);
> +	do_trace_rt_spinlock_released(lock, current);
>  	rt_spin_lock_fastunlock(&lock->lock, rt_spin_lock_slowunlock);
>  	migrate_enable();
>  	rcu_read_unlock();
> diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
> index 546aaf058b9e..185ffc1e7015 100644
> --- a/kernel/locking/rtmutex_common.h
> +++ b/kernel/locking/rtmutex_common.h
> @@ -25,6 +25,20 @@
>   * @pi_tree_entry:	pi node to enqueue into the mutex owner waiters tree
>   * @task:		task reference to the blocked task
>   */
> +
> +#ifdef CONFIG_RT_SPIN_LOCK_TRACING
> +#define do_trace_rt_spinlock_acquire(lock, task) \
> +	trace_rt_spinlock_acquire(&lock->dep_map, task)
> +#define do_trace_rt_spinlock_acquired(lock, task) \
> +	trace_rt_spinlock_acquired(&lock->dep_map, task)
> +#define do_trace_rt_spinlock_released(lock, task) \
> +	trace_rt_spinlock_released(&lock->dep_map, task)
> +#else
> +#define do_trace_rt_spinlock_acquire(lock, task) do {} while(0)
> +#define do_trace_rt_spinlock_acquired(lock, task) do {} while(0)
> +#define do_trace_rt_spinlock_released(lock, task) do {} while(0)
> +#endif
> +

Acked-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>

Although it will need to be accepted by Peter Zijlstra.

-- Steve


>  struct rt_mutex_waiter {
>  	struct rb_node          tree_entry;
>  	struct rb_node          pi_tree_entry;