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.
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);
