nptl/tpp.c

   1 /* Thread Priority Protect helpers.
   2    Copyright (C) 2006-2024 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <atomic.h>
  21 #include <errno.h>
  22 #include <pthreadP.h>
  23 #include <sched.h>
  24 #include <stdlib.h>
  25 #include <atomic.h>
  26
  27 int __sched_fifo_min_prio = -1;
  28 libc_hidden_data_def (__sched_fifo_min_prio)
  29 int __sched_fifo_max_prio = -1;
  30 libc_hidden_data_def (__sched_fifo_max_prio)
  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 libc_hidden_def (__init_sched_fifo_prio)
  51
  52 int
  53 __pthread_tpp_change_priority (int previous_prio, int new_prio)
  54 {
  55   struct pthread *self = THREAD_SELF;
  56   struct priority_protection_data *tpp = THREAD_GETMEM (self, tpp);
  57   int fifo_min_prio = atomic_load_relaxed (&__sched_fifo_min_prio);
  58   int fifo_max_prio = atomic_load_relaxed (&__sched_fifo_max_prio);
  59
  60   if (tpp == NULL)
  61     {
  62       /* See __init_sched_fifo_prio.  We need both the min and max prio,
  63          so need to check both, and run initialization if either one is
  64          not initialized.  The memory model's write-read coherence rule
  65          makes this work.  */
  66       if (fifo_min_prio == -1 || fifo_max_prio == -1)
  67         {
  68           __init_sched_fifo_prio ();
  69           fifo_min_prio = atomic_load_relaxed (&__sched_fifo_min_prio);
  70           fifo_max_prio = atomic_load_relaxed (&__sched_fifo_max_prio);
  71         }
  72
  73       size_t size = sizeof *tpp;
  74       size += (fifo_max_prio - fifo_min_prio + 1)
  75               * sizeof (tpp->priomap[0]);
  76       tpp = calloc (size, 1);
  77       if (tpp == NULL)
  78         return ENOMEM;
  79       tpp->priomax = fifo_min_prio - 1;
  80       THREAD_SETMEM (self, tpp, tpp);
  81     }
  82
  83   assert (new_prio == -1
  84           || (new_prio >= fifo_min_prio
  85               && new_prio <= fifo_max_prio));
  86   assert (previous_prio == -1
  87           || (previous_prio >= fifo_min_prio
  88               && previous_prio <= fifo_max_prio));
  89
  90   int priomax = tpp->priomax;
  91   int newpriomax = priomax;
  92   if (new_prio != -1)
  93     {
  94       if (tpp->priomap[new_prio - fifo_min_prio] + 1 == 0)
  95         return EAGAIN;
  96       ++tpp->priomap[new_prio - fifo_min_prio];
  97       if (new_prio > priomax)
  98         newpriomax = new_prio;
  99     }
 100
 101   if (previous_prio != -1)
 102     {
 103       if (--tpp->priomap[previous_prio - fifo_min_prio] == 0
 104           && priomax == previous_prio
 105           && previous_prio > new_prio)
 106         {
 107           int i;
 108           for (i = previous_prio - 1; i >= fifo_min_prio; --i)
 109             if (tpp->priomap[i - fifo_min_prio])
 110               break;
 111           newpriomax = i;
 112         }
 113     }
 114
 115   if (priomax == newpriomax)
 116     return 0;
 117
 118   /* See CREATE THREAD NOTES in nptl/pthread_create.c.  */
 119   lll_lock (self->lock, LLL_PRIVATE);
 120
 121   tpp->priomax = newpriomax;
 122
 123   int result = 0;
 124
 125   if ((self->flags & ATTR_FLAG_SCHED_SET) == 0)
 126     {
 127       if (__sched_getparam (self->tid, &self->schedparam) != 0)
 128         result = errno;
 129       else
 130         self->flags |= ATTR_FLAG_SCHED_SET;
 131     }
 132
 133   if ((self->flags & ATTR_FLAG_POLICY_SET) == 0)
 134     {
 135       self->schedpolicy = __sched_getscheduler (self->tid);
 136       if (self->schedpolicy == -1)
 137         result = errno;
 138       else
 139         self->flags |= ATTR_FLAG_POLICY_SET;
 140     }
 141
 142   if (result == 0)
 143     {
 144       struct sched_param sp = self->schedparam;
 145       if (sp.sched_priority < newpriomax || sp.sched_priority < priomax)
 146         {
 147           if (sp.sched_priority < newpriomax)
 148             sp.sched_priority = newpriomax;
 149
 150           if (__sched_setscheduler (self->tid, self->schedpolicy, &sp) < 0)
 151             result = errno;
 152         }
 153     }
 154
 155   lll_unlock (self->lock, LLL_PRIVATE);
 156
 157   return result;
 158 }
 159 libc_hidden_def (__pthread_tpp_change_priority)
 160
 161 int
 162 __pthread_current_priority (void)
 163 {
 164   struct pthread *self = THREAD_SELF;
 165   if ((self->flags & (ATTR_FLAG_POLICY_SET | ATTR_FLAG_SCHED_SET))
 166       == (ATTR_FLAG_POLICY_SET | ATTR_FLAG_SCHED_SET))
 167     return self->schedparam.sched_priority;
 168
 169   int result = 0;
 170
 171   /* See CREATE THREAD NOTES in nptl/pthread_create.c.  */
 172   lll_lock (self->lock, LLL_PRIVATE);
 173
 174   if ((self->flags & ATTR_FLAG_SCHED_SET) == 0)
 175     {
 176       if (__sched_getparam (self->tid, &self->schedparam) != 0)
 177         result = -1;
 178       else
 179         self->flags |= ATTR_FLAG_SCHED_SET;
 180     }
 181
 182   if ((self->flags & ATTR_FLAG_POLICY_SET) == 0)
 183     {
 184       self->schedpolicy = __sched_getscheduler (self->tid);
 185       if (self->schedpolicy == -1)
 186         result = -1;
 187       else
 188         self->flags |= ATTR_FLAG_POLICY_SET;
 189     }
 190
 191   if (result != -1)
 192     result = self->schedparam.sched_priority;
 193
 194   lll_unlock (self->lock, LLL_PRIVATE);
 195
 196   return result;
 197 }
 198 libc_hidden_def (__pthread_current_priority)