Re: [PATCH v3] staging: vc04_services: Fix RCU dereference check

Stefan Wahren
2022-01-23T17:32:40Z

Am 31.12.21 um 20:54 schrieb Padmanabha Srinivasaiah:
> In service_callback path RCU dereferenced pointer struct vchiq_service
> need to be accessed inside rcu read-critical section.
>
> Also userdata/user_service part of vchiq_service is accessed around
> different synchronization mechanism, getting an extra reference to a
> pointer keeps sematics simpler and avoids prolonged graceperiod.
>
> Accessing vchiq_service with rcu_read_[lock/unlock] fixes below issue.
>
> [ 32.201659] =============================
> [ 32.201664] WARNING: suspicious RCU usage
> [ 32.201670] 5.15.11-rt24-v8+ #3 Not tainted
> [ 32.201680] -----------------------------
> [ 32.201685] drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h:529 suspicious rcu_dereference_check() usage!
> [ 32.201695]
> [ 32.201695] other info that might help us debug this:
> [ 32.201695]
> [ 32.201700]
> [ 32.201700] rcu_scheduler_active = 2, debug_locks = 1
> [ 32.201708] no locks held by vchiq-slot/0/98.
> [ 32.201715]
> [ 32.201715] stack backtrace:
> [ 32.201723] CPU: 1 PID: 98 Comm: vchiq-slot/0 Not tainted 5.15.11-rt24-v8+ #3
> [ 32.201733] Hardware name: Raspberry Pi 4 Model B Rev 1.4 (DT)
> [ 32.201739] Call trace:
> [ 32.201742] dump_backtrace+0x0/0x1b8
> [ 32.201772] show_stack+0x20/0x30
> [ 32.201784] dump_stack_lvl+0x8c/0xb8
> [ 32.201799] dump_stack+0x18/0x34
> [ 32.201808] lockdep_rcu_suspicious+0xe4/0xf8
> [ 32.201817] service_callback+0x124/0x400
> [ 32.201830] slot_handler_func+0xf60/0x1e20
> [ 32.201839] kthread+0x19c/0x1a8
> [ 32.201849] ret_from_fork+0x10/0x20
>
> Signed-off-by: Padmanabha Srinivasaiah <treasure4paddy@gmail.com>

Tested-by: Stefan Wahren <stefan.wahren@i2se.com>

Thanks