linux-kernel - [PATCH v2] seqlock,lockdep: Only check for preemption

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Message-Id: <20210507234713.86097-1-dave@stgolabs.net>
Date:   Fri,  7 May 2021 16:47:13 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     a.darwish@...utronix.de
Cc:     bigeasy@...utronix.de, peterz@...radead.org, tglx@...utronix.de,
        shung-hsi.yu@...e.com, dave@...olabs.net,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH v2] seqlock,lockdep: Only check for preemption_disabled in non-rt

This silences the writer hitting this nonsensical warning on PREEMPT_RT.

Reported-by: Shung-Hsi Yu <shung-hsi.yu@...e.com>
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---

v2: Resending because I had left out some small comments I had meant to add.

 include/linux/seqlock.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index f61e34fbaaea..2ce3e1efc9a9 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -268,7 +268,9 @@ static inline bool __seqprop_preemptible(const seqcount_t *s)
 
 static inline void __seqprop_assert(const seqcount_t *s)
 {
+#ifndef CONFIG_PREEMPT_RT
 	lockdep_assert_preemption_disabled();
+#endif
 }
 
 #define __SEQ_RT	IS_ENABLED(CONFIG_PREEMPT_RT)
@@ -529,6 +531,8 @@ static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass)
  * only if the seqcount write serialization lock is associated, and
  * preemptible.  If readers can be invoked from hardirq or softirq
  * context, interrupts or bottom halves must be respectively disabled.
+ * The PREEMPT_RT case relies on the reader serializing via LOCK+UNLOCK,
+ * so the context is preemptible.
  */
 #define write_seqcount_begin(s)						\
 do {									\
-- 
2.26.2