linux-kernel - Re: [PATCH v3 2/2] rcu/rcuscale: Stop kfree_scale_thread thread(s) after unloading rcuscale

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Message-ID: <a4a3e103-78b3-4be3-80b8-bbae7b1bb2f4@paulmck-laptop>
Date:   Tue, 21 Mar 2023 12:23:58 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     Qiuxu Zhuo <qiuxu.zhuo@...el.com>, frederic@...nel.org,
        jiangshanlai@...il.com, joel@...lfernandes.org,
        josh@...htriplett.org, linux-kernel@...r.kernel.org,
        mathieu.desnoyers@...icios.com, quic_neeraju@...cinc.com,
        rcu@...r.kernel.org, rostedt@...dmis.org
Subject: Re: [PATCH v3 2/2] rcu/rcuscale: Stop kfree_scale_thread thread(s)
 after unloading rcuscale

On Tue, Mar 21, 2023 at 08:47:51AM -0700, Davidlohr Bueso wrote:
> On Tue, 21 Mar 2023, 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")
> > Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@...el.com>
> 
> Reviewed-by: Davidlohr Bueso <dave@...olabs.net>

Much better, thank you both!

But unfortunately, these patches do not apply cleanly.  Qiuxu Zhuo,
could you please forward port these to the -rcu "dev" branch [1]?

						Thanx, Paul

[1] https://mirrors.edge.kernel.org/pub/linux/kernel/people/paulmck/rcutodo.html