2020-02-28 08:20:21

by Amol Grover

Subject: [PATCH] ipmi: Fix RCU list lockdep debugging warnings

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 <[email protected]>
Suggested-by: Paul E. McKenney <[email protected]>
Signed-off-by: Amol Grover <[email protected]>
---
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) {
--
2.25.0

2020-02-28 11:49:27

by John Garry

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 <[email protected]>
> Suggested-by: Paul E. McKenney <[email protected]>
> Signed-off-by: Amol Grover <[email protected]>

Tested-by: John Garry <[email protected]>

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) {
>

2020-02-28 17:45:47

by Corey Minyard

Subject: Re: [PATCH] ipmi: Fix RCU list lockdep debugging warnings

On Fri, Feb 28, 2020 at 01:47:33PM +0530, 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.

Thanks, this is queued for 5.7, and I hadded John Garry's test by.

-corey

>
> 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 <[email protected]>
> Suggested-by: Paul E. McKenney <[email protected]>
> Signed-off-by: Amol Grover <[email protected]>
> ---
> 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) {
> --
> 2.25.0
>