Commit a4dd9925 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: create new rcu_access_index() and use in mce 



The MCE subsystem needs to sample an RCU-protected index outside of
any protection for that index.  If this was a pointer, we would use
rcu_access_pointer(), but there is no corresponding rcu_access_index().
This commit therefore creates an rcu_access_index() and applies it
to MCE.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: default avatarZdenek Kabelac <zkabelac@redhat.com>
parent 0ce790e7

arch/x86/kernel/cpu/mcheck/mce.c

+1 −1
Original line number Diff line number Diff line
@@ -1626,7 +1626,7 @@ out: 
static unsigned int mce_poll(struct file *file, poll_table *wait)

{

	poll_wait(file, &mce_wait, wait);

	if (rcu_dereference_check_mce(mcelog.next))

	if (rcu_access_index(mcelog.next))

		return POLLIN | POLLRDNORM;

	if (!mce_apei_read_done && apei_check_mce())

		return POLLIN | POLLRDNORM;

include/linux/rcupdate.h

+20 −0
Original line number Diff line number Diff line
@@ -339,6 +339,12 @@ extern int rcu_my_thread_group_empty(void); 
		((typeof(*p) __force __kernel *)(p)); \

	})



#define __rcu_access_index(p, space) \

	({ \

		typeof(p) _________p1 = ACCESS_ONCE(p); \

		rcu_dereference_sparse(p, space); \

		(_________p1); \

	})

#define __rcu_dereference_index_check(p, c) \

	({ \

		typeof(p) _________p1 = ACCESS_ONCE(p); \
@@ -428,6 +434,20 @@ extern int rcu_my_thread_group_empty(void); 


#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/



/**

 * rcu_access_index() - fetch RCU index with no dereferencing

 * @p: The index to read

 *

 * Return the value of the specified RCU-protected index, but omit the

 * smp_read_barrier_depends() and keep the ACCESS_ONCE().  This is useful

 * when the value of this index is accessed, but the index is not

 * dereferenced, for example, when testing an RCU-protected index against

 * -1.  Although rcu_access_index() may also be used in cases where

 * update-side locks prevent the value of the index from changing, you

 * should instead use rcu_dereference_index_protected() for this use case.

 */

#define rcu_access_index(p) __rcu_access_index((p), __rcu)



/**

 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking

 * @p: The pointer to read, prior to dereferencing

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