linux-kernel - Re: [PATCH v3] drivers: char: ipmi: ipmi_msghandler: Pass lockdep expression to RCU lists

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Message-ID: <20200212214956.GT2935@paulmck-ThinkPad-P72>
Date:   Wed, 12 Feb 2020 13:49:56 -0800
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Corey Minyard <minyard@....org>
Cc:     Amol Grover <frextrite@...il.com>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>
Subject: Re: [PATCH v3] drivers: char: ipmi: ipmi_msghandler: Pass lockdep
 expression to RCU lists

On Wed, Feb 12, 2020 at 07:45:52AM -0600, Corey Minyard wrote:
> On Fri, Jan 17, 2020 at 06:55:22PM +0530, Amol Grover wrote:
> > intf->cmd_rcvrs is traversed with list_for_each_entry_rcu
> > outside an RCU read-side critical section but under the
> > protection of intf->cmd_rcvrs_mutex.
> > 
> > ipmi_interfaces is traversed using list_for_each_entry_rcu
> > outside an RCU read-side critical section but under the protection
> > of ipmi_interfaces_mutex.
> > 
> > Hence, add the corresponding lockdep expression to the list traversal
> > primitive to silence false-positive lockdep warnings, and
> > harden RCU lists.
> > 
> > Add macro for the corresponding lockdep expression to make the code
> > clean and concise.
> > 
> > Signed-off-by: Amol Grover <frextrite@...il.com>
> 
> After reading everything, I think this is correct, but I would like
> Paul's stamp of approval on this.

Acked-by: Paul E. McKenney <paulmck@...nel.org>

But note that I did not trace the locking in the case of ipmi_add_smi().
I did the others, so lockdep can do the last one.  ;-)

							Thanx, Paul

> Thanks,
> 
> -corey
> 
> > ---
> > v3:
> > - Remove rcu_read_lock_held() from lockdep expression since it is
> >   implicitly checked.
> > - Remove unintended macro usage.
> >  
> > v2:
> > - Fix sparse error
> >   CHECK: Alignment should match open parenthesis
> > 
> >  drivers/char/ipmi/ipmi_msghandler.c | 14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> > index cad9563f8f48..64ba16dcb681 100644
> > --- a/drivers/char/ipmi/ipmi_msghandler.c
> > +++ b/drivers/char/ipmi/ipmi_msghandler.c
> > @@ -618,6 +618,8 @@ static DEFINE_MUTEX(ipmidriver_mutex);
> >  
> >  static LIST_HEAD(ipmi_interfaces);
> >  static DEFINE_MUTEX(ipmi_interfaces_mutex);
> > +#define ipmi_interfaces_mutex_held() \
> > +	lockdep_is_held(&ipmi_interfaces_mutex)
> >  static struct srcu_struct ipmi_interfaces_srcu;
> >  
> >  /*
> > @@ -1321,7 +1323,8 @@ static void _ipmi_destroy_user(struct ipmi_user *user)
> >  	 * synchronize_srcu()) then free everything in that list.
> >  	 */
> >  	mutex_lock(&intf->cmd_rcvrs_mutex);
> > -	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link) {
> > +	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link,
> > +				lockdep_is_held(&intf->cmd_rcvrs_mutex)) {
> >  		if (rcvr->user == user) {
> >  			list_del_rcu(&rcvr->link);
> >  			rcvr->next = rcvrs;
> > @@ -1599,7 +1602,8 @@ static struct cmd_rcvr *find_cmd_rcvr(struct ipmi_smi *intf,
> >  {
> >  	struct cmd_rcvr *rcvr;
> >  
> > -	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link) {
> > +	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link,
> > +				lockdep_is_held(&intf->cmd_rcvrs_mutex)) {
> >  		if ((rcvr->netfn == netfn) && (rcvr->cmd == cmd)
> >  					&& (rcvr->chans & (1 << chan)))
> >  			return rcvr;
> > @@ -1614,7 +1618,8 @@ static int is_cmd_rcvr_exclusive(struct ipmi_smi *intf,
> >  {
> >  	struct cmd_rcvr *rcvr;
> >  
> > -	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link) {
> > +	list_for_each_entry_rcu(rcvr, &intf->cmd_rcvrs, link,
> > +				lockdep_is_held(&intf->cmd_rcvrs_mutex)) {
> >  		if ((rcvr->netfn == netfn) && (rcvr->cmd == cmd)
> >  					&& (rcvr->chans & chans))
> >  			return 0;
> > @@ -3450,7 +3455,8 @@ int ipmi_add_smi(struct module         *owner,
> >  	/* Look for a hole in the numbers. */
> >  	i = 0;
> >  	link = &ipmi_interfaces;
> > -	list_for_each_entry_rcu(tintf, &ipmi_interfaces, link) {
> > +	list_for_each_entry_rcu(tintf, &ipmi_interfaces, link,
> > +				ipmi_interfaces_mutex_held()) {
> >  		if (tintf->intf_num != i) {
> >  			link = &tintf->link;
> >  			break;
> > -- 
> > 2.24.1
> >