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authorTorvald Riegel <triegel@redhat.com>2014-11-25 19:48:56 +0100
committerTorvald Riegel <triegel@redhat.com>2014-11-26 10:07:20 +0100
commitcdcb42d7f786fe5ee1ca60065924d0b5c6649dd0 (patch)
tree302e5e92ddcc5996250b9d5ee3ab578afaa128ef /nptl/tpp.c
parentc82f5c0ce5c1c0180fca311ceb29fd2d59da7441 (diff)
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Fix synchronization of TPP min/max priorities.
* nptl/tpp.c (__init_sched_fifo_prio, __pthread_tpp_change_priority): Change synchronization of __sched_fifo_min_prio and __sched_fifo_max_prio. * nptl/pthread_mutexattr_getprioceiling.c (pthread_mutexattr_getprioceiling): Likewise. * nptl/pthread_mutexattr_setprioceiling.c (pthread_mutexattr_setprioceiling): Likewise. * nptl/pthread_mutex_init.c (__pthread_mutex_init): Likewise. * nptl/pthread_mutex_setprioceiling.c (pthread_mutex_setprioceiling): Likewise.
Diffstat (limited to 'nptl/tpp.c')
-rw-r--r--nptl/tpp.c54
1 files changed, 38 insertions, 16 deletions
diff --git a/nptl/tpp.c b/nptl/tpp.c
index ee9a2fe..9cfeea1 100644
--- a/nptl/tpp.c
+++ b/nptl/tpp.c
@@ -23,17 +23,29 @@
#include <pthreadP.h>
#include <sched.h>
#include <stdlib.h>
+#include <atomic.h>
int __sched_fifo_min_prio = -1;
int __sched_fifo_max_prio = -1;
+/* We only want to initialize __sched_fifo_min_prio and __sched_fifo_max_prio
+ once. The standard solution would be similar to pthread_once, but then
+ readers would need to use an acquire fence. In this specific case,
+ initialization is comprised of just idempotent writes to two variables
+ that have an initial value of -1. Therefore, we can treat each variable as
+ a separate, at-least-once initialized value. This enables using just
+ relaxed MO loads and stores, but requires that consumers check for
+ initialization of each value that is to be used; see
+ __pthread_tpp_change_priority for an example.
+ */
void
__init_sched_fifo_prio (void)
{
- __sched_fifo_max_prio = sched_get_priority_max (SCHED_FIFO);
- atomic_write_barrier ();
- __sched_fifo_min_prio = sched_get_priority_min (SCHED_FIFO);
+ atomic_store_relaxed (&__sched_fifo_max_prio,
+ sched_get_priority_max (SCHED_FIFO));
+ atomic_store_relaxed (&__sched_fifo_min_prio,
+ sched_get_priority_min (SCHED_FIFO));
}
int
@@ -41,49 +53,59 @@ __pthread_tpp_change_priority (int previous_prio, int new_prio)
{
struct pthread *self = THREAD_SELF;
struct priority_protection_data *tpp = THREAD_GETMEM (self, tpp);
+ int fifo_min_prio = atomic_load_relaxed (&__sched_fifo_min_prio);
+ int fifo_max_prio = atomic_load_relaxed (&__sched_fifo_max_prio);
if (tpp == NULL)
{
- if (__sched_fifo_min_prio == -1)
- __init_sched_fifo_prio ();
+ /* See __init_sched_fifo_prio. We need both the min and max prio,
+ so need to check both, and run initialization if either one is
+ not initialized. The memory model's write-read coherence rule
+ makes this work. */
+ if (fifo_min_prio == -1 || fifo_max_prio == -1)
+ {
+ __init_sched_fifo_prio ();
+ fifo_min_prio = atomic_load_relaxed (&__sched_fifo_min_prio);
+ fifo_max_prio = atomic_load_relaxed (&__sched_fifo_max_prio);
+ }
size_t size = sizeof *tpp;
- size += (__sched_fifo_max_prio - __sched_fifo_min_prio + 1)
+ size += (fifo_max_prio - fifo_min_prio + 1)
* sizeof (tpp->priomap[0]);
tpp = calloc (size, 1);
if (tpp == NULL)
return ENOMEM;
- tpp->priomax = __sched_fifo_min_prio - 1;
+ tpp->priomax = fifo_min_prio - 1;
THREAD_SETMEM (self, tpp, tpp);
}
assert (new_prio == -1
- || (new_prio >= __sched_fifo_min_prio
- && new_prio <= __sched_fifo_max_prio));
+ || (new_prio >= fifo_min_prio
+ && new_prio <= fifo_max_prio));
assert (previous_prio == -1
- || (previous_prio >= __sched_fifo_min_prio
- && previous_prio <= __sched_fifo_max_prio));
+ || (previous_prio >= fifo_min_prio
+ && previous_prio <= fifo_max_prio));
int priomax = tpp->priomax;
int newpriomax = priomax;
if (new_prio != -1)
{
- if (tpp->priomap[new_prio - __sched_fifo_min_prio] + 1 == 0)
+ if (tpp->priomap[new_prio - fifo_min_prio] + 1 == 0)
return EAGAIN;
- ++tpp->priomap[new_prio - __sched_fifo_min_prio];
+ ++tpp->priomap[new_prio - fifo_min_prio];
if (new_prio > priomax)
newpriomax = new_prio;
}
if (previous_prio != -1)
{
- if (--tpp->priomap[previous_prio - __sched_fifo_min_prio] == 0
+ if (--tpp->priomap[previous_prio - fifo_min_prio] == 0
&& priomax == previous_prio
&& previous_prio > new_prio)
{
int i;
- for (i = previous_prio - 1; i >= __sched_fifo_min_prio; --i)
- if (tpp->priomap[i - __sched_fifo_min_prio])
+ for (i = previous_prio - 1; i >= fifo_min_prio; --i)
+ if (tpp->priomap[i - fifo_min_prio])
break;
newpriomax = i;
}