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Date: Fri, 28 Feb 2020 11:49:01 +0000 From: John Garry <john.garry@...wei.com> To: Amol Grover <frextrite@...il.com>, Corey Minyard <minyard@....org>, "Arnd Bergmann" <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org> CC: <openipmi-developer@...ts.sourceforge.net>, <linux-kernel@...r.kernel.org>, <linux-kernel-mentees@...ts.linuxfoundation.org>, Joel Fernandes <joel@...lfernandes.org>, Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>, "Paul E . Mckenney" <paulmck@...nel.org> Subject: Re: [PATCH] ipmi: Fix RCU list lockdep debugging warnings On 28/02/2020 08:17, Amol Grover wrote: > It is completely safe to traverse ipmi_interfaces and > intf->users under SRCU read lock using list_for_each_entry_rcu(). > Tell lockdep about it as well else it will show false-positive > warnings as the one below. > > Fixes the following false-positive warning and others that may follow. > > [ 29.772408] ============================= > [ 29.776863] WARNING: suspicious RCU usage > [ 29.780915] 5.6.0-rc3-00001-g907305ae6618-dirty #1755 Not tainted > [ 29.787046] ----------------------------- > [ 29.791100] drivers/char/ipmi/ipmi_msghandler.c:744 RCU-list traversed in > non-reader section!! > > Reported-by: John Garry <john.garry@...wei.com> > Suggested-by: Paul E. McKenney <paulmck@...nel.org> > Signed-off-by: Amol Grover <frextrite@...il.com> Tested-by: John Garry <john.garry@...wei.com> Thanks, the warnings have gone away with this > --- > drivers/char/ipmi/ipmi_msghandler.c | 18 ++++++++++++------ > 1 file changed, 12 insertions(+), 6 deletions(-) > > diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c > index cad9563f8f48..d202022c69de 100644 > --- a/drivers/char/ipmi/ipmi_msghandler.c > +++ b/drivers/char/ipmi/ipmi_msghandler.c > @@ -741,7 +741,8 @@ int ipmi_smi_watcher_register(struct ipmi_smi_watcher *watcher) > list_add(&watcher->link, &smi_watchers); > > index = srcu_read_lock(&ipmi_interfaces_srcu); > - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { > + list_for_each_entry_rcu(intf, &ipmi_interfaces, link, > + srcu_read_lock_held(&ipmi_interfaces_srcu)) { > int intf_num = READ_ONCE(intf->intf_num); > > if (intf_num == -1) > @@ -1188,7 +1189,8 @@ int ipmi_create_user(unsigned int if_num, > return -ENOMEM; > > index = srcu_read_lock(&ipmi_interfaces_srcu); > - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { > + list_for_each_entry_rcu(intf, &ipmi_interfaces, link, > + srcu_read_lock_held(&ipmi_interfaces_srcu)) { > if (intf->intf_num == if_num) > goto found; > } > @@ -1241,7 +1243,8 @@ int ipmi_get_smi_info(int if_num, struct ipmi_smi_info *data) > struct ipmi_smi *intf; > > index = srcu_read_lock(&ipmi_interfaces_srcu); > - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { > + list_for_each_entry_rcu(intf, &ipmi_interfaces, link, > + srcu_read_lock_held(&ipmi_interfaces_srcu)) { > if (intf->intf_num == if_num) > goto found; > } > @@ -4098,7 +4101,8 @@ static int handle_read_event_rsp(struct ipmi_smi *intf, > * getting events. > */ > index = srcu_read_lock(&intf->users_srcu); > - list_for_each_entry_rcu(user, &intf->users, link) { > + list_for_each_entry_rcu(user, &intf->users, link, > + srcu_read_lock_held(&intf->users_srcu)) { > if (!user->gets_events) > continue; > > @@ -4453,7 +4457,8 @@ static void handle_new_recv_msgs(struct ipmi_smi *intf) > int index; > > index = srcu_read_lock(&intf->users_srcu); > - list_for_each_entry_rcu(user, &intf->users, link) { > + list_for_each_entry_rcu(user, &intf->users, link, > + srcu_read_lock_held(&intf->users_srcu)) { > if (user->handler->ipmi_watchdog_pretimeout) > user->handler->ipmi_watchdog_pretimeout( > user->handler_data); > @@ -4746,7 +4751,8 @@ static void ipmi_timeout(struct timer_list *unused) > return; > > index = srcu_read_lock(&ipmi_interfaces_srcu); > - list_for_each_entry_rcu(intf, &ipmi_interfaces, link) { > + list_for_each_entry_rcu(intf, &ipmi_interfaces, link, > + srcu_read_lock_held(&ipmi_interfaces_srcu)) { > if (atomic_read(&intf->event_waiters)) { > intf->ticks_to_req_ev--; > if (intf->ticks_to_req_ev == 0) { >
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