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mce: Stop using array-index-based RCU primitives 

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 <paulmck@linux.vnet.ibm.com>
Cc: linux-edac@vger.kernel.org
Cc: Tony Luck <tony.luck@intel.com>
Acked-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Paul E. McKenney 2015-04-19 18:16:02 -07:00
parent 7d0ae8086b
commit e90328b87e
1 changed files with 7 additions and 4 deletions
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11
arch/x86/kernel/cpu/mcheck/mce.c
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@ -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 @@ static ssize_t mce_chrdev_read(struct file *filp, char __user *ubuf,
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;