nptl/nptl-stack.c

   1 /* Stack cache management for NPTL.
   2    Copyright (C) 2002-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
   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    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <nptl-stack.h>
  21 #include <ldsodefs.h>
  22
  23 /* Maximum size in kB of cache.  40MiBi by default.  */
  24 static const size_t stack_cache_maxsize = 40 * 1024 * 1024;
  25
  26 void
  27 __nptl_stack_list_del (list_t *elem)
  28 {
  29   GL (dl_in_flight_stack) = (uintptr_t) elem;
  30
  31   atomic_write_barrier ();
  32
  33   list_del (elem);
  34
  35   atomic_write_barrier ();
  36
  37   GL (dl_in_flight_stack) = 0;
  38 }
  39 libc_hidden_def (__nptl_stack_list_del)
  40
  41 void
  42 __nptl_stack_list_add (list_t *elem, list_t *list)
  43 {
  44   GL (dl_in_flight_stack) = (uintptr_t) elem | 1;
  45
  46   atomic_write_barrier ();
  47
  48   list_add (elem, list);
  49
  50   atomic_write_barrier ();
  51
  52   GL (dl_in_flight_stack) = 0;
  53 }
  54 libc_hidden_def (__nptl_stack_list_add)
  55
  56 void
  57 __nptl_free_stacks (size_t limit)
  58 {
  59   /* We reduce the size of the cache.  Remove the last entries until
  60      the size is below the limit.  */
  61   list_t *entry;
  62   list_t *prev;
  63
  64   /* Search from the end of the list.  */
  65   list_for_each_prev_safe (entry, prev, &GL (dl_stack_cache))
  66     {
  67       struct pthread *curr;
  68
  69       curr = list_entry (entry, struct pthread, list);
  70       if (__nptl_stack_in_use (curr))
  71         {
  72           /* Unlink the block.  */
  73           __nptl_stack_list_del (entry);
  74
  75           /* Account for the freed memory.  */
  76           GL (dl_stack_cache_actsize) -= curr->stackblock_size;
  77
  78           /* Free the memory associated with the ELF TLS.  */
  79           _dl_deallocate_tls (TLS_TPADJ (curr), false);
  80
  81           /* Remove this block.  This should never fail.  If it does
  82              something is really wrong.  */
  83           if (__munmap (curr->stackblock, curr->stackblock_size) != 0)
  84             abort ();
  85
  86           /* Maybe we have freed enough.  */
  87           if (GL (dl_stack_cache_actsize) <= limit)
  88             break;
  89         }
  90     }
  91 }
  92
  93 /* Add a stack frame which is not used anymore to the stack.  Must be
  94    called with the cache lock held.  */
  95 static inline void
  96 __attribute ((always_inline))
  97 queue_stack (struct pthread *stack)
  98 {
  99   /* We unconditionally add the stack to the list.  The memory may
 100      still be in use but it will not be reused until the kernel marks
 101      the stack as not used anymore.  */
 102   __nptl_stack_list_add (&stack->list, &GL (dl_stack_cache));
 103
 104   GL (dl_stack_cache_actsize) += stack->stackblock_size;
 105   if (__glibc_unlikely (GL (dl_stack_cache_actsize) > stack_cache_maxsize))
 106     __nptl_free_stacks (stack_cache_maxsize);
 107 }
 108
 109 void
 110 __nptl_deallocate_stack (struct pthread *pd)
 111 {
 112   lll_lock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 113
 114   /* Remove the thread from the list of threads with user defined
 115      stacks.  */
 116   __nptl_stack_list_del (&pd->list);
 117
 118   /* Not much to do.  Just free the mmap()ed memory.  Note that we do
 119      not reset the 'used' flag in the 'tid' field.  This is done by
 120      the kernel.  If no thread has been created yet this field is
 121      still zero.  */
 122   if (__glibc_likely (! pd->user_stack))
 123     (void) queue_stack (pd);
 124   else
 125     /* Free the memory associated with the ELF TLS.  */
 126     _dl_deallocate_tls (TLS_TPADJ (pd), false);
 127
 128   lll_unlock (GL (dl_stack_cache_lock), LLL_PRIVATE);
 129 }
 130 libc_hidden_def (__nptl_deallocate_stack)