From: "Paul E. McKenney" <paul...@linux.vnet.ibm.com>
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 <paul...@linux.vnet.ibm.com>
Cc: linux-e...@vger.kernel.org
Cc: Tony Luck <tony.l...@intel.com>
Cc: Borislav Petkov <b...@alien8.de>
---
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
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