>From 60b91dea371067c529587c504be0543350d1c0e5 Mon Sep 17 00:00:00 2001
From: John Kacur <jkacur@xxxxxxxxxx>
Date: Mon, 19 Sep 2011 10:29:42 +0200
Subject: [PATCH] =?UTF-8?q?preempt-rt:=20VERSION=202:=20Fix=20build=20error:=20section=20of=20=E2=80=98tasklist=5Flock=E2=80=99=20conflicts=20with=20previous=20declaration?=
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This fixes the following build error for the preempt-rt kernel.
make kernel/fork.o
CC kernel/fork.o
kernel/fork.c:90: error: section of ʽtasklist_lockʼ conflicts with previous declaration
make[2]: *** [kernel/fork.o] Error 1
make[1]: *** [kernel/fork.o] Error 2
The rt kernel cache aligns the RWLOCK in DEFINE_RWLOCK by default.
The non-rt kernels explicitly cache align only the tasklist_lock in
kernel/fork.c
That can create a build conflict. This fixes the build problem by making the
non-rt kernels cache align RWLOCKs by default. The side effect is that
the other RWLOCKs are also cache aligned for non-rt.
This is a short term solution for rt only.
The longer term solution would be to push the cache aligned DEFINE_RWLOCK
to mainline. If there are objections, then we could create a
DEFINE_RWLOCK_CACHE_ALIGNED or something of that nature.
Comments? Objections?
Signed-off-by: John Kacur <jkacur@xxxxxxxxxx>
---
include/linux/rwlock_types.h | 3 ++-
kernel/fork.c | 2 +-
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/include/linux/rwlock_types.h b/include/linux/rwlock_types.h
index 5317cd9..d0da966 100644
--- a/include/linux/rwlock_types.h
+++ b/include/linux/rwlock_types.h
@@ -47,6 +47,7 @@ typedef struct {
RW_DEP_MAP_INIT(lockname) }
#endif
-#define DEFINE_RWLOCK(x) rwlock_t x = __RW_LOCK_UNLOCKED(x)
+#define DEFINE_RWLOCK(name) \
+ rwlock_t name __cacheline_aligned_in_smp = __RW_LOCK_UNLOCKED(name)
#endif /* __LINUX_RWLOCK_TYPES_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index aa5fe26..8487ae7 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -87,7 +87,7 @@ int max_threads; /* tunable limit on nr_threads */
DEFINE_PER_CPU(unsigned long, process_counts) = 0;
-__cacheline_aligned DEFINE_RWLOCK(tasklist_lock); /* outer */
+DEFINE_RWLOCK(tasklist_lock); /* outer */
#ifdef CONFIG_PROVE_RCU
int lockdep_tasklist_lock_is_held(void)
--
1.7.2.3
