Re: [PATCH v4 2/2] rcu/rcuscale: Stop kfree_scale_thread thread(s) after unloading rcuscale

[Paul E. McKenney]

On Wed, Mar 22, 2023 at 07:42:41PM +0800, Qiuxu Zhuo wrote:
> When running the 'kfree_rcu_test' test case with commands [1] the call
> trace [2] was thrown. This was because the kfree_scale_thread thread(s)
> still run after unloading rcuscale and torture modules. Fix the call
> trace by invoking kfree_scale_cleanup() from rcu_scale_cleanup() when
> removing the rcuscale module.
> 
> [1] modprobe rcuscale kfree_rcu_test=1
>     // After some time
>     rmmod rcuscale
>     rmmod torture
> 
> [2] BUG: unable to handle page fault for address: ffffffffc0601a87
>     #PF: supervisor instruction fetch in kernel mode
>     #PF: error_code(0x0010) - not-present page
>     PGD 11de4f067 P4D 11de4f067 PUD 11de51067 PMD 112f4d067 PTE 0
>     Oops: 0010 [#1] PREEMPT SMP NOPTI
>     CPU: 1 PID: 1798 Comm: kfree_scale_thr Not tainted 6.3.0-rc1-rcu+ #1
>     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
>     RIP: 0010:0xffffffffc0601a87
>     Code: Unable to access opcode bytes at 0xffffffffc0601a5d.
>     RSP: 0018:ffffb25bc2e57e18 EFLAGS: 00010297
>     RAX: 0000000000000000 RBX: ffffffffc061f0b6 RCX: 0000000000000000
>     RDX: 0000000000000000 RSI: ffffffff962fd0de RDI: ffffffff962fd0de
>     RBP: ffffb25bc2e57ea8 R08: 0000000000000000 R09: 0000000000000000
>     R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000000
>     R13: 0000000000000000 R14: 000000000000000a R15: 00000000001c1dbe
>     FS:  0000000000000000(0000) GS:ffff921fa2200000(0000) knlGS:0000000000000000
>     CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>     CR2: ffffffffc0601a5d CR3: 000000011de4c006 CR4: 0000000000370ee0
>     DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>     DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>     Call Trace:
>      <TASK>
>      ? kvfree_call_rcu+0xf0/0x3a0
>      ? kthread+0xf3/0x120
>      ? kthread_complete_and_exit+0x20/0x20
>      ? ret_from_fork+0x1f/0x30
>      </TASK>
>     Modules linked in: rfkill sunrpc ... [last unloaded: torture]
>     CR2: ffffffffc0601a87
>     ---[ end trace 0000000000000000 ]---
> 
> Fixes: e6e78b004fa7 ("rcuperf: Add kfree_rcu() performance Tests")
> Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>

Much better, thank you!

I queued and pushed both of them.

							Thanx, Paul

> ---
>  kernel/rcu/rcuscale.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
> index 7e8965b0827a..d1221731c7cf 100644
> --- a/kernel/rcu/rcuscale.c
> +++ b/kernel/rcu/rcuscale.c
> @@ -797,6 +797,11 @@ rcu_scale_cleanup(void)
>  	if (gp_exp && gp_async)
>  		SCALEOUT_ERRSTRING("No expedited async GPs, so went with async!");
>  
> +	if (kfree_rcu_test) {
> +		kfree_scale_cleanup();
> +		return;
> +	}
> +
>  	if (torture_cleanup_begin())
>  		return;
>  	if (!cur_ops) {
> -- 
> 2.17.1
>