Re: [rcu:rcu/dev 39/39] kernel/rcu/tree_exp.h:163:9: sparse: incorrect type in argument 1 (different modifiers)

[Boqun Feng <boqun.feng@gmail.com>]

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On Thu, Mar 08, 2018 at 04:34:43PM -0800, Paul E. McKenney wrote:
> On Fri, Mar 09, 2018 at 06:52:34AM +0800, Boqun Feng wrote:
> > On Fri, Mar 09, 2018 at 05:41:27AM +0800, kbuild test robot wrote:
> > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/dev
> > > head:   b8909ec707bb5beba94e7c7d62cc6b3115ceae50
> > > commit: b8909ec707bb5beba94e7c7d62cc6b3115ceae50 [39/39] rcu: Protect all sync_rcu_preempt_exp_done() with rcu_node lock
> > > reproduce:
> > >         # apt-get install sparse
> > >         git checkout b8909ec707bb5beba94e7c7d62cc6b3115ceae50
> > >         make ARCH=x86_64 allmodconfig
> > >         make C=1 CF=-D__CHECK_ENDIAN__
> > > 
> > > 
> > > sparse warnings: (new ones prefixed by >>)
> > > 
> > [...]
> > >    kernel/rcu/tree.c:345:6: sparse: symbol 'rcu_dynticks_curr_cpu_in_eqs' was not declared. Should it be static?
> > >    kernel/rcu/tree.c:3953:21: sparse: incorrect type in argument 1 (different modifiers) @@    expected int ( *threadfn )( ... ) @@    got int ( [noreint ( *threadfn )( ... ) @@
> > >    kernel/rcu/tree.c:3953:21:    expected int ( *threadfn )( ... )
> > >    kernel/rcu/tree.c:3953:21:    got int ( [noreturn] *<noident> )( ... )
> > > >> kernel/rcu/tree_exp.h:163:9: sparse: incorrect type in argument 1 (different modifiers) @@    expected struct lockdep_map const *lock @@    got strustruct lockdep_map const *lock @@
> > >    kernel/rcu/tree_exp.h:163:9:    expected struct lockdep_map const *lock
> > >    kernel/rcu/tree_exp.h:163:9:    got struct lockdep_map [noderef] *<noident>
> > >    kernel/rcu/tree.c:1752:9: sparse: context imbalance in 'rcu_start_future_gp' - different lock contexts for basic block
> > >    kernel/rcu/tree.c:2786:9: sparse: context imbalance in 'force_qs_rnp' - different lock contexts for basic block
> > >    kernel/rcu/tree.c:2849:25: sparse: context imbalance in 'force_quiescent_state' - unexpected unlock
> > >    kernel/rcu/tree_exp.h:203:9: sparse: too many warnings
> > > 
> > > vim +163 kernel/rcu/tree_exp.h
> > > 
> > >    151	
> > >    152	/*
> > >    153	 * Return non-zero if there is no RCU expedited grace period in progress
> > >    154	 * for the specified rcu_node structure, in other words, if all CPUs and
> > >    155	 * tasks covered by the specified rcu_node structure have done their bit
> > >    156	 * for the current expedited grace period.  Works only for preemptible
> > >    157	 * RCU -- other RCU implementation use other means.
> > >    158	 *
> > >    159	 * Caller must hold the specificed rcu_node structure's ->lock
> > >    160	 */
> > >    161	static bool sync_rcu_preempt_exp_done(struct rcu_node *rnp)
> > >    162	{
> > >  > 163		lockdep_assert_held(&rnp->lock);
> > 
> > OK, so we need ACCESS_PRIVATE() to visit ->lock in rcu_node. I will
> > introduce something like:
> > 
> > 	#define rcu_node_lock_assert_held(rnp) lockdep_assert_held(&ACCESS_PRIVATE(rnp, lock))
> > 
> > in v3.
> 
> Or use this, which is in kernel/rcu/rcu.h:
> 
> #define raw_lockdep_assert_held_rcu_node(p)				\
> 	lockdep_assert_held(&ACCESS_PRIVATE(p, lock))
> 

Good point, thank you for pointing this out ;-)

Regards,
Boqun

> 							Thanx, Paul
> 

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