On 2020-09-08 16:56:20 [+0200], Mike Galbraith wrote:
> On Tue, 2020-09-08 at 14:19 +0200, Sebastian Andrzej Siewior wrote:
> >
> > This has nothing to do with the bridge but with the fact that you use a
> > non standard queue class (something else than pfifo_fast).
>
> That must be SUSE, I don't muck about in network land. I downloaded a
> whole library of RFCs decades ago, but turns out that one of those is
> all the bedtime story you'll ever need. Huge waste of bandwidth :)
I see.
This should cure it:
Subject: [PATCH] net: Properly annotate the try-lock for the seqlock
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>
---
include/net/net_seq_lock.h | 9 ---------
include/net/sch_generic.h | 10 +++++++++-
2 files changed, 9 insertions(+), 10 deletions(-)
diff --git a/include/net/net_seq_lock.h b/include/net/net_seq_lock.h
index 95a497a72e511..67710bace7418 100644
--- a/include/net/net_seq_lock.h
+++ b/include/net/net_seq_lock.h
@@ -6,15 +6,6 @@
# define net_seq_begin(__r) read_seqbegin(__r)
# define net_seq_retry(__r, __s) read_seqretry(__r, __s)
-static inline int try_write_seqlock(seqlock_t *sl)
-{
- if (spin_trylock(&sl->lock)) {
- write_seqcount_begin(&sl->seqcount);
- return 1;
- }
- return 0;
-}
-
#else
# define net_seqlock_t seqcount_t
# define net_seq_begin(__r) read_seqcount_begin(__r)
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 796ac453d9519..40be4443b6bdb 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.seqcount;
+ /*
+ * Variant of write_seqcount_t_begin() telling lockdep that a
+ * trylock was attempted.
+ */
+ raw_write_seqcount_t_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
--
2.28.0
> -Mike
Sebastian
