Subject: rwlocks: Fix section mismatch From: John Kacur Date: Mon, 19 Sep 2011 11:09:27 +0200 (CEST) Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/3.14/patches-3.14.10-rt7.tar.xz 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 tasklist_lock 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 Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/alpine.LFD.2.00.1109191104010.23118@localhost6.localdomain6 Signed-off-by: Thomas Gleixner --- include/linux/rwlock_types.h | 3 ++- kernel/fork.c | 2 +- 2 files changed, 3 insertions(+), 2 deletions(-) --- 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 */ --- a/kernel/fork.c +++ b/kernel/fork.c @@ -94,7 +94,7 @@ int max_threads; /* tunable limit on nr 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)