nptl/nptl-stack.c

   1 /* Stack cache management for NPTL.
   2    Copyright (C) 2002-2022 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 <nptl-stack.h>
  20 #include <ldsodefs.h>
  21 #include <pthreadP.h>
  22
  23 size_t __nptl_stack_cache_maxsize = 40 * 1024 * 1024;
  24
  25 void
  26 __nptl_stack_list_del (list_t *elem)
  27 {
  28   GL (dl_in_flight_stack) = (uintptr_t) elem;
  29
  30   atomic_write_barrier ();
  31
  32   list_del (elem);
  33
  34   atomic_write_barrier ();
  35
  36   GL (dl_in_flight_stack) = 0;
  37 }
  38 libc_hidden_def (__nptl_stack_list_del)
  39
  40 void
  41 __nptl_stack_list_add (list_t *elem, list_t *list)
  42 {
  43   GL (dl_in_flight_stack) = (uintptr_t) elem | 1;
  44
  45   atomic_write_barrier ();
  46
  47   list_add (elem, list);
  48
  49   atomic_write_barrier ();
  50
  51   GL (dl_in_flight_stack) = 0;
  52 }
  53 libc_hidden_def (__nptl_stack_list_add)
  54
  55 void
  56 __nptl_free_stacks (size_t limit)
  57 {
  58   /* We reduce the size of the cache.  Remove the last entries until
  59      the size is below the limit.  */
  60   list_t *entry;
  61   list_t *prev;
  62
  63   /* Search from the end of the list.  */
  64   list_for_each_prev_safe (entry, prev, &GL (dl_stack_cache))
  65     {
  66       struct pthread *curr;
  67
  68       curr = list_entry (entry, struct pthread, list);
  69       if (__nptl_stack_in_use (curr))
  70         {
  71           /* Unlink the block.  */
  72           __nptl_stack_list_del (entry);
  73
  74           /* Account for the freed memory.  */
  75           GL (dl_stack_cache_actsize) -= curr->stackblock_size;
  76
  77           /* Free the memory associated with the ELF TLS.  */
  78           _dl_deallocate_tls (TLS_TPADJ (curr), false);
  79
  80           /* Remove this block.  This should never fail.  If it does
  81              something is really wrong.  */
  82           if (__munmap (curr->stackblock, curr->stackblock_size) != 0)
  83             abort ();
  84
  85           /* Maybe we have freed enough.  */
  86           if (GL (dl_stack_cache_actsize) <= limit)
  87             break;
  88         }
  89     }
  90 }
  91
  92 /* Add a stack frame which is not used anymore to the stack.  Must be
  93    called with the cache lock held.  */
  94 static inline void
  95 __attribute ((always_inline))
  96 queue_stack (struct pthread *stack)
  97 {
  98   /* We unconditionally add the stack to the list.  The memory may
  99      still be in use but it will not be reused until the kernel marks
 100      the stack as not used anymore.  */
 101   __nptl_stack_list_add (&stack->list, &GL (dl_stack_cache));
 102
 103   GL (dl_stack_cache_actsize) += stack->stackblock_size;
 104   if (__glibc_unlikely (GL (dl_stack_cache_actsize)
 105                         > __nptl_stack_cache_maxsize))
 106     __nptl_free_stacks (__nptl_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)
 131
 132 /* This function is internal (it has a GLIBC_PRIVATE) version, but it
 133    is widely used (either via weak symbol, or dlsym) to obtain the
 134    __static_tls_size value.  This value is then used to adjust the
 135    value of the stack size attribute, so that applications receive the
 136    full requested stack size, not diminished by the TCB and static TLS
 137    allocation on the stack.  Once the TCB is separately allocated,
 138    this function should be removed or renamed (if it is still
 139    necessary at that point).  */
 140 size_t
 141 __pthread_get_minstack (const pthread_attr_t *attr)
 142 {
 143   return (GLRO(dl_pagesize) + __nptl_tls_static_size_for_stack ()
 144           + PTHREAD_STACK_MIN);
 145 }
 146 libc_hidden_def (__pthread_get_minstack)