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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-04-01 07:15:14 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-04-01 07:27:31 -0700 |
| commit | a4dd99250dc49031e6a92a895dbcc230a4832083 (patch) | |
| tree | 3d0b6f45620f66044400ea14a6af019bf0af67e7 | |
| parent | 0ce790e7d736cedc563e1fb4e998babf5a4dbc3d (diff) | |
| download | linux-a4dd99250dc49031e6a92a895dbcc230a4832083.tar.bz2 | |
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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Zdenek Kabelac <zkabelac@redhat.com>
| -rw-r--r-- | arch/x86/kernel/cpu/mcheck/mce.c | 2 | ||||
| -rw-r--r-- | include/linux/rcupdate.h | 20 |
2 files changed, 21 insertions, 1 deletions
diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index 5a05ef63eb4a..3385ea26f684 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -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; diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index af5614856285..ff422d2b7f90 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -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); \ @@ -429,6 +435,20 @@ 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 * @c: The conditions under which the dereference will take place |