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

[Corey Minyard <minyard@acm.org>]

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@gmail.com>

After reading everything, I think this is correct, but I would like
Paul's stamp of approval on this.

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
> 
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