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

[Breno Leitao]

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.
> 
> -----
> 
> =============================
> 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.

You probably should use list_for_each_entry_srcu() instead of the
list_for_each_entry_rcu().

This problem is still happening in 6.12-rc5.