From: "Paul E. McKenney" <[email protected]> Because mce is arch-specific x86 code, there is little or no performance benefit of using rcu_dereference_index_check() over using smp_load_acquire(). It also turns out that mce is the only place that array-index-based RCU is used, and it would be convenient to drop this portion of the RCU API.
This patch therefore changes rcu_dereference_index_check() uses to smp_load_acquire(), but keeping the lockdep diagnostics, and also changes rcu_access_index() uses to READ_ONCE(). Signed-off-by: Paul E. McKenney <[email protected]> Cc: [email protected] Cc: Tony Luck <[email protected]> Cc: Borislav Petkov <[email protected]> --- arch/x86/kernel/cpu/mcheck/mce.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index e535533d5ab8..1fd04a02d90a 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -53,9 +53,12 @@ static DEFINE_MUTEX(mce_chrdev_read_mutex); #define rcu_dereference_check_mce(p) \ - rcu_dereference_index_check((p), \ - rcu_read_lock_sched_held() || \ - lockdep_is_held(&mce_chrdev_read_mutex)) +({ \ + rcu_lockdep_assert(rcu_read_lock_sched_held() || \ + lockdep_is_held(&mce_chrdev_read_mutex), \ + "suspicious rcu_dereference_check_mce() usage"); \ + smp_load_acquire(&(p)); \ +}) #define CREATE_TRACE_POINTS #include <trace/events/mce.h> @@ -1884,7 +1887,7 @@ out: static unsigned int mce_chrdev_poll(struct file *file, poll_table *wait) { poll_wait(file, &mce_chrdev_wait, wait); - if (rcu_access_index(mcelog.next)) + if (READ_ONCE(mcelog.next)) return POLLIN | POLLRDNORM; if (!mce_apei_read_done && apei_check_mce()) return POLLIN | POLLRDNORM; -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
