On Fri, Apr 06, 2018 at 06:22:11PM +0100, Mark Rutland wrote:
> Digging a bit, I also thing that our ct_user_exit and ct_user_enter
> usage is on dodgy ground today.
>
> For example, in el0_dbg we call do_debug_exception() *before* calling
> ct_user_exit. Which I believe means we'd use RCU while supposedly in an
> extended quiescent period, which would be bad.
It seems this is the case. I can trigger the following by having GDB
place a SW breakpoint:
[ 51.217947] =============================
[ 51.217953] WARNING: suspicious RCU usage
[ 51.217961] 4.16.0 #4 Not tainted
[ 51.217966] -----------------------------
[ 51.217974] ./include/linux/rcupdate.h:632 rcu_read_lock() used illegally while idle!
[ 51.217980]
[ 51.217980] other info that might help us debug this:
[ 51.217980]
[ 51.217987]
[ 51.217987] RCU used illegally from idle CPU!
[ 51.217987] rcu_scheduler_active = 2, debug_locks = 1
[ 51.217992] RCU used illegally from extended quiescent state!
[ 51.217999] 1 lock held by ls/2412:
[ 51.218004] #0: (rcu_read_lock){....}, at: [<0000000092efbdd5>] brk_handler+0x0/0x198
[ 51.218041]
[ 51.218041] stack backtrace:
[ 51.218049] CPU: 2 PID: 2412 Comm: ls Not tainted 4.16.0 #4
[ 51.218055] Hardware name: ARM Juno development board (r1) (DT)
[ 51.218061] Call trace:
[ 51.218070] dump_backtrace+0x0/0x1c8
[ 51.218078] show_stack+0x14/0x20
[ 51.218087] dump_stack+0xac/0xe4
[ 51.218096] lockdep_rcu_suspicious+0xcc/0x110
[ 51.218103] brk_handler+0x144/0x198
[ 51.218110] do_debug_exception+0x9c/0x190
[ 51.218116] el0_dbg+0x14/0x20
We will need to fix this before we can fiddle with kick_all_cpus_sync().
Thanks,
Mark.
