[PATCH RT v2] net: Add missing seqcount_release() to qdisc_run_end()

* [PATCH RT v2] net: Add missing seqcount_release() to qdisc_run_end()
@ 2020-11-14 20:12 Tom Zanussi
  2020-11-16 17:22 ` Sebastian Andrzej Siewior
  0 siblings, 1 reply; 3+ messages in thread
From: Tom Zanussi @ 2020-11-14 20:12 UTC (permalink / raw)
  To: Sebastian Andrzej Siewior, Steven Rostedt; +Cc: linux-rt-users, Mike Galbraith

Hi Sebastian and Steve,

This patch fixes a problem [1] I saw when backporting 'net: Properly
annotate the try-lock for the seqlock" from 5.4 to 4.19 which also
looks like it should apply to -devel.

This was tested on 5.14 but applies cleanly to rt-devel as well.

Thanks,

Tom

[1] https://lore.kernel.org/linux-rt-users/20201110153853.463368981@goodmis.org/T/#m0be3a1290486f3493828dedcf7f06d5fbba092a8 

v2: Mike Galbraith pointed out that write_sequnlock() already contains
__raw_write_seqcount_end().

---
The patch ('net: Properly annotate the try-lock for the seqlock") adds
a seqcount_acquire() in qdisc_run_begin() but omits the corresponding
seqcount_release() in qdisc_run_end().

Add it unconditionally, since qdisc_run_end() is never called unless
qdisc_run_begin() succeeds, and if it succeeds, seqcount_acquire()
will have been called.

Signed-off-by: Tom Zanussi <zanussi@kernel.org>
---
 include/net/sch_generic.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 112d2dca8b08..221470e38031 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -192,7 +192,10 @@ static inline bool qdisc_run_begin(struct Qdisc *qdisc)
 static inline void qdisc_run_end(struct Qdisc *qdisc)
 {
 #ifdef CONFIG_PREEMPT_RT
+	seqcount_t *s = &qdisc->running.seqcount;
+
 	write_sequnlock(&qdisc->running);
+	seqcount_release(&s->dep_map, 1, _RET_IP_);
 #else
 	write_seqcount_end(&qdisc->running);
 #endif
-- 
2.17.1



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