On 5/22/19 2:18 PM, Paul E. McKenney wrote:
> On Tue, May 21, 2019 at 04:48:43PM -0400, Waiman Long wrote:
>> It is found that when debugging options are turned on, the
>> rcu_read_lock() function may not be inlined at all. That will make
>> it harder to debug RCU related problem as the print_lock() function
>> in lockdep will print "rcu_read_lock()" instead of the caller of
>> rcu_read_lock() function. For example,
>>
>> [ 10.579995] =============================
>> [ 10.584033] WARNING: suspicious RCU usage
>> [ 10.588074] 4.18.0.memcg_v2+ #1 Not tainted
>> [ 10.593162] -----------------------------
>> [ 10.597203] include/linux/rcupdate.h:281 Illegal context switch in
>> RCU read-side critical section!
>> [ 10.606220]
>> [ 10.606220] other info that might help us debug this:
>> [ 10.606220]
>> [ 10.614280]
>> [ 10.614280] rcu_scheduler_active = 2, debug_locks = 1
>> [ 10.620853] 3 locks held by systemd/1:
>> [ 10.624632] #0: (____ptrval____) (&type->i_mutex_dir_key#5){.+.+}, at: lookup_slow+0x42/0x70
>> [ 10.633232] #1: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70
>> [ 10.640954] #2: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70
>>
>> To make sure that the proper caller of rcu_read_lock() is shown, we
>> have to force the inlining of the rcu_read_lock() function.
>>
>> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> Good point, queued! I reworked the commit log as follows, is this OK?
>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit c006ffd7b607f8ee216f6a7a6d845b9514881e92
> Author: Waiman Long <longman@xxxxxxxxxx>
> Date: Tue May 21 16:48:43 2019 -0400
>
> rcu: Force inlining of rcu_read_lock()
>
> When debugging options are turned on, the rcu_read_lock() function
> might not be inlined. This results in lockdep's print_lock() function
> printing "rcu_read_lock+0x0/0x70" instead of rcu_read_lock()'s caller.
> For example:
>
> [ 10.579995] =============================
> [ 10.584033] WARNING: suspicious RCU usage
> [ 10.588074] 4.18.0.memcg_v2+ #1 Not tainted
> [ 10.593162] -----------------------------
> [ 10.597203] include/linux/rcupdate.h:281 Illegal context switch in
> RCU read-side critical section!
> [ 10.606220]
> [ 10.606220] other info that might help us debug this:
> [ 10.606220]
> [ 10.614280]
> [ 10.614280] rcu_scheduler_active = 2, debug_locks = 1
> [ 10.620853] 3 locks held by systemd/1:
> [ 10.624632] #0: (____ptrval____) (&type->i_mutex_dir_key#5){.+.+}, at: lookup_slow+0x42/0x70
> [ 10.633232] #1: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70
> [ 10.640954] #2: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70
>
> These "rcu_read_lock+0x0/0x70" strings are not providing any useful
> information. This commit therefore forces inlining of the rcu_read_lock()
> function so that rcu_read_lock()'s caller is instead shown.
>
Your modification make sense to me.
Thanks,
Longman
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
>
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index 534c05d529b5..a8ed624da555 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -588,7 +588,7 @@ static inline void rcu_preempt_sleep_check(void) { }
> * read-side critical sections may be preempted and they may also block, but
> * only when acquiring spinlocks that are subject to priority inheritance.
> */
> -static inline void rcu_read_lock(void)
> +static __always_inline void rcu_read_lock(void)
> {
> __rcu_read_lock();
> __acquire(RCU);
>
