nptl/tpp.c

   1 /* Thread Priority Protect helpers.
   2    Copyright (C) 2006-2015 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Jakub Jelinek <jakub@redhat.com>, 2006.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <assert.h>
  21 #include <atomic.h>
  22 #include <errno.h>
  23 #include <pthreadP.h>
  24 #include <sched.h>
  25 #include <stdlib.h>
  26 #include <atomic.h>
  27
  28
  29 int __sched_fifo_min_prio = -1;
  30 int __sched_fifo_max_prio = -1;
  31
  32 /* We only want to initialize __sched_fifo_min_prio and __sched_fifo_max_prio
  33    once.  The standard solution would be similar to pthread_once, but then
  34    readers would need to use an acquire fence.  In this specific case,
  35    initialization is comprised of just idempotent writes to two variables
  36    that have an initial value of -1.  Therefore, we can treat each variable as
  37    a separate, at-least-once initialized value.  This enables using just
  38    relaxed MO loads and stores, but requires that consumers check for
  39    initialization of each value that is to be used; see
  40    __pthread_tpp_change_priority for an example.
  41  */
  42 void
  43 __init_sched_fifo_prio (void)
  44 {
  45   atomic_store_relaxed (&__sched_fifo_max_prio,
  46                         sched_get_priority_max (SCHED_FIFO));
  47   atomic_store_relaxed (&__sched_fifo_min_prio,
  48                         sched_get_priority_min (SCHED_FIFO));
  49 }
  50
  51 int
  52 __pthread_tpp_change_priority (int previous_prio, int new_prio)
  53 {
  54   struct pthread *self = THREAD_SELF;
  55   struct priority_protection_data *tpp = THREAD_GETMEM (self, tpp);
  56   int fifo_min_prio = atomic_load_relaxed (&__sched_fifo_min_prio);
  57   int fifo_max_prio = atomic_load_relaxed (&__sched_fifo_max_prio);
  58
  59   if (tpp == NULL)
  60     {
  61       /* See __init_sched_fifo_prio.  We need both the min and max prio,
  62          so need to check both, and run initialization if either one is
  63          not initialized.  The memory model's write-read coherence rule
  64          makes this work.  */
  65       if (fifo_min_prio == -1 || fifo_max_prio == -1)
  66         {
  67           __init_sched_fifo_prio ();
  68           fifo_min_prio = atomic_load_relaxed (&__sched_fifo_min_prio);
  69           fifo_max_prio = atomic_load_relaxed (&__sched_fifo_max_prio);
  70         }
  71
  72       size_t size = sizeof *tpp;
  73       size += (fifo_max_prio - fifo_min_prio + 1)
  74               * sizeof (tpp->priomap[0]);
  75       tpp = calloc (size, 1);
  76       if (tpp == NULL)
  77         return ENOMEM;
  78       tpp->priomax = fifo_min_prio - 1;
  79       THREAD_SETMEM (self, tpp, tpp);
  80     }
  81
  82   assert (new_prio == -1
  83           || (new_prio >= fifo_min_prio
  84               && new_prio <= fifo_max_prio));
  85   assert (previous_prio == -1
  86           || (previous_prio >= fifo_min_prio
  87               && previous_prio <= fifo_max_prio));
  88
  89   int priomax = tpp->priomax;
  90   int newpriomax = priomax;
  91   if (new_prio != -1)
  92     {
  93       if (tpp->priomap[new_prio - fifo_min_prio] + 1 == 0)
  94         return EAGAIN;
  95       ++tpp->priomap[new_prio - fifo_min_prio];
  96       if (new_prio > priomax)
  97         newpriomax = new_prio;
  98     }
  99
 100   if (previous_prio != -1)
 101     {
 102       if (--tpp->priomap[previous_prio - fifo_min_prio] == 0
 103           && priomax == previous_prio
 104           && previous_prio > new_prio)
 105         {
 106           int i;
 107           for (i = previous_prio - 1; i >= fifo_min_prio; --i)
 108             if (tpp->priomap[i - fifo_min_prio])
 109               break;
 110           newpriomax = i;
 111         }
 112     }
 113
 114   if (priomax == newpriomax)
 115     return 0;
 116
 117   lll_lock (self->lock, LLL_PRIVATE);
 118
 119   tpp->priomax = newpriomax;
 120
 121   int result = 0;
 122
 123   if ((self->flags & ATTR_FLAG_SCHED_SET) == 0)
 124     {
 125       if (__sched_getparam (self->tid, &self->schedparam) != 0)
 126         result = errno;
 127       else
 128         self->flags |= ATTR_FLAG_SCHED_SET;
 129     }
 130
 131   if ((self->flags & ATTR_FLAG_POLICY_SET) == 0)
 132     {
 133       self->schedpolicy = __sched_getscheduler (self->tid);
 134       if (self->schedpolicy == -1)
 135         result = errno;
 136       else
 137         self->flags |= ATTR_FLAG_POLICY_SET;
 138     }
 139
 140   if (result == 0)
 141     {
 142       struct sched_param sp = self->schedparam;
 143       if (sp.sched_priority < newpriomax || sp.sched_priority < priomax)
 144         {
 145           if (sp.sched_priority < newpriomax)
 146             sp.sched_priority = newpriomax;
 147
 148           if (__sched_setscheduler (self->tid, self->schedpolicy, &sp) < 0)
 149             result = errno;
 150         }
 151     }
 152
 153   lll_unlock (self->lock, LLL_PRIVATE);
 154
 155   return result;
 156 }
 157
 158 int
 159 __pthread_current_priority (void)
 160 {
 161   struct pthread *self = THREAD_SELF;
 162   if ((self->flags & (ATTR_FLAG_POLICY_SET | ATTR_FLAG_SCHED_SET))
 163       == (ATTR_FLAG_POLICY_SET | ATTR_FLAG_SCHED_SET))
 164     return self->schedparam.sched_priority;
 165
 166   int result = 0;
 167
 168   lll_lock (self->lock, LLL_PRIVATE);
 169
 170   if ((self->flags & ATTR_FLAG_SCHED_SET) == 0)
 171     {
 172       if (__sched_getparam (self->tid, &self->schedparam) != 0)
 173         result = -1;
 174       else
 175         self->flags |= ATTR_FLAG_SCHED_SET;
 176     }
 177
 178   if ((self->flags & ATTR_FLAG_POLICY_SET) == 0)
 179     {
 180       self->schedpolicy = __sched_getscheduler (self->tid);
 181       if (self->schedpolicy == -1)
 182         result = -1;
 183       else
 184         self->flags |= ATTR_FLAG_POLICY_SET;
 185     }
 186
 187   if (result != -1)
 188     result = self->schedparam.sched_priority;
 189
 190   lll_unlock (self->lock, LLL_PRIVATE);
 191
 192   return result;
 193 }