Re: [PATCH] ipmi: msghandler: Suppress suspicious RCU usage warning

[Corey Minyard <minyard@acm.org>]

On Thu, Nov 19, 2020 at 03:08:39PM +0800, Qinglang Miao wrote:
> while running ipmi, ipmi_smi_watcher_register() caused
> a suspicious RCU usage warning.

Thanks.  I had looked at this and found it was ok, but I hand't spent
the time to figure out how to suppress it.  It's in my next queue.

-corey

> 
> -----
> 
> =============================
> WARNING: suspicious RCU usage
> 5.10.0-rc3+ #1 Not tainted
> -----------------------------
> drivers/char/ipmi/ipmi_msghandler.c:750 RCU-list traversed in non-reader section!!
> other info that might help us debug this:
> rcu_scheduler_active = 2, debug_locks = 1
> 2 locks held by syz-executor.0/4254:
> stack backtrace:
> CPU: 0 PID: 4254 Comm: syz-executor.0 Not tainted 5.10.0-rc3+ #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/ 01/2014
> Call Trace:
> dump_stack+0x19d/0x200
> ipmi_smi_watcher_register+0x2d3/0x340 [ipmi_msghandler]
> acpi_ipmi_init+0xb1/0x1000 [acpi_ipmi]
> do_one_initcall+0x149/0x7e0
> do_init_module+0x1ef/0x700
> load_module+0x3467/0x4140
> __do_sys_finit_module+0x10d/0x1a0
> do_syscall_64+0x34/0x80
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x468ded
> 
> -----
> 
> It is safe because smi_watchers_mutex is locked and srcu_read_lock
> has been used, so simply pass lockdep_is_held() to the
> list_for_each_entry_rcu() to suppress this warning.
> 
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Signed-off-by: Qinglang Miao <miaoqinglang@huawei.com>
> ---
>  drivers/char/ipmi/ipmi_msghandler.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index 8774a3b8f..c44ad1846 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -747,7 +747,8 @@ 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,
> +			lockdep_is_held(&smi_watchers_mutex)) {
>  		int intf_num = READ_ONCE(intf->intf_num);
>  
>  		if (intf_num == -1)
> -- 
> 2.23.0
>