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Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/l…
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…inux/kernel/git/tip/linux-2.6-tip

* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  rcu: create new rcu_access_index() and use in mce
  WARN_ON_SMP(): Add comment to explain ({0;})
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torvalds committed Apr 4, 2011
2 parents 4acfaf8 + 5679027 commit fb9a7d7
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Showing 3 changed files with 28 additions and 1 deletion.
2 changes: 1 addition & 1 deletion arch/x86/kernel/cpu/mcheck/mce.c
Original file line number Diff line number Diff line change
Expand Up @@ -1626,7 +1626,7 @@ static ssize_t mce_read(struct file *filp, char __user *ubuf, size_t usize,
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;
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7 changes: 7 additions & 0 deletions include/asm-generic/bug.h
Original file line number Diff line number Diff line change
Expand Up @@ -194,6 +194,13 @@ extern void warn_slowpath_null(const char *file, const int line);
#ifdef CONFIG_SMP
# define WARN_ON_SMP(x) WARN_ON(x)
#else
/*
* Use of ({0;}) because WARN_ON_SMP(x) may be used either as
* a stand alone line statement or as a condition in an if ()
* statement.
* A simple "0" would cause gcc to give a "statement has no effect"
* warning.
*/
# define WARN_ON_SMP(x) ({0;})
#endif

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20 changes: 20 additions & 0 deletions include/linux/rcupdate.h
Original file line number Diff line number Diff line change
Expand Up @@ -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); \
Expand Down Expand Up @@ -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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