Hi Steve,
On Tue, 2020-11-10 at 10:38 -0500, Steven Rostedt wrote:
> 5.4.74-rt42-rc2 stable review patch.
> If anyone has any objections, please let me know.
>
> ------------------
>
> From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
>
> In patch
> ("net/Qdisc: use a seqlock instead seqcount")
>
> the seqcount has been replaced with a seqlock to allow to reader to
> boost the preempted writer.
> The try_write_seqlock() acquired the lock with a try-lock but the
> seqcount annotation was "lock".
>
> Opencode write_seqcount_t_begin() and use the try-lock annotation for
> lockdep.
>
> Reported-by: Mike Galbraith <efault@xxxxxx>
> Cc: stable-rt@xxxxxxxxxxxxxxx
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
> ---
> include/linux/seqlock.h | 9 ---------
> include/net/sch_generic.h | 10 +++++++++-
> 2 files changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> index e5207897c33e..f390293974ea 100644
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -489,15 +489,6 @@ static inline void write_seqlock(seqlock_t *sl)
> __raw_write_seqcount_begin(&sl->seqcount);
> }
>
> -static inline int try_write_seqlock(seqlock_t *sl)
> -{
> - if (spin_trylock(&sl->lock)) {
> - __raw_write_seqcount_begin(&sl->seqcount);
> - return 1;
> - }
> - return 0;
> -}
> -
> static inline void write_sequnlock(seqlock_t *sl)
> {
> __raw_write_seqcount_end(&sl->seqcount);
> diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
> index e6afb4b9cede..112d2dca8b08 100644
> --- a/include/net/sch_generic.h
> +++ b/include/net/sch_generic.h
> @@ -168,8 +168,16 @@ static inline bool qdisc_run_begin(struct Qdisc
> *qdisc)
> return false;
> }
> #ifdef CONFIG_PREEMPT_RT
> - if (try_write_seqlock(&qdisc->running))
> + if (spin_trylock(&qdisc->running.lock)) {
> + seqcount_t *s = &qdisc->running.seqcount;
> + /*
> + * Variant of write_seqcount_t_begin() telling lockdep
> that a
> + * trylock was attempted.
> + */
> + __raw_write_seqcount_begin(s);
> + seqcount_acquire(&s->dep_map, 0, 1, _RET_IP_);
> return true;
> + }
> return false;
> #else
> /* Variant of write_seqcount_begin() telling lockdep a trylock
I applied this to 4.19 and saw some splat with my 'debug-full'
configuration, so tried 5.4 and saw the same thing:
[ 30.573698] BUG: workqueue leaked lock or atomic: kworker/1:4/0x00000000/143
last function: wireless_nlevent_process
[ 30.573707] 1 lock held by kworker/1:4/143:
[ 30.573708] #0: ffffffff8e981d80 (noop_qdisc.running#2){+.+.}, at: __do_softirq+0xca/0x561
[ 30.573715] CPU: 1 PID: 143 Comm: kworker/1:4 Not tainted 5.4.74-rt42-rt-test-full-debug #1
[ 30.573716] Hardware name: LENOVO 4236L51/4236L51, BIOS 83ET59WW (1.29 ) 06/01/2011
[ 30.573720] Workqueue: events wireless_nlevent_process
[ 30.573721] Call Trace:
[ 30.573724] dump_stack+0x71/0x9b
[ 30.573728] process_one_work+0x533/0x760
[ 30.573731] worker_thread+0x39/0x3f0
[ 30.573733] ? process_one_work+0x760/0x760
[ 30.573734] kthread+0x165/0x180
[ 30.573736] ? __kthread_create_on_node+0x180/0x180
[ 30.573737] ret_from_fork+0x3a/0x50
[ 30.629329] wlp3s0: authenticate with 84:1b:5e:41:5e:4d
[ 30.634864] wlp3s0: send auth to 84:1b:5e:41:5e:4d (try 1/3)
[ 30.638433] wlp3s0: authenticated
[ 30.642250] wlp3s0: associate with 84:1b:5e:41:5e:4d (try 1/3)
[ 30.645704] wlp3s0: RX AssocResp from 84:1b:5e:41:5e:4d (capab=0x411 status=0 aid=6)
[ 30.650803] wlp3s0: associated
[ 30.656764] ================================================
[ 30.656765] WARNING: lock held when returning to user space!
[ 30.656766] 5.4.74-rt42-rt-test-full-debug #1 Not tainted
[ 30.656767] ------------------------------------------------
[ 30.656768] wpa_supplicant/836 is leaving the kernel with locks still held!
[ 30.656769] 1 lock held by wpa_supplicant/836:
[ 30.656770] #0: ffff98f1c9622280 (&dev->qdisc_running_key){+.+.}, at: packet_sendmsg+0xec1/0x1ad0
Let me know if you want me to send you my .config or the full output (a
bunch more of the above).
Thanks,
Tom
