lib/util/talloc_stack.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    Implement a stack of talloc contexts
   4    Copyright (C) Volker Lendecke 2007
   5    Copyright (C) Jeremy Allison 2009 - made thread safe.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20 */
  21
  22 /*
  23  * Implement a stack of talloc frames.
  24  *
  25  * When a new talloc stackframe is allocated with talloc_stackframe(), then
  26  * the TALLOC_CTX returned with talloc_tos() is reset to that new
  27  * frame. Whenever that stack frame is TALLOC_FREE()'ed, then the reverse
  28  * happens: The previous talloc_tos() is restored.
  29  *
  30  * This API is designed to be robust in the sense that if someone forgets to
  31  * TALLOC_FREE() a stackframe, then the next outer one correctly cleans up and
  32  * resets the talloc_tos().
  33  *
  34  * This robustness feature means that we can't rely on a linked list with
  35  * talloc destructors because in a hierarchy of talloc destructors the parent
  36  * destructor is called before its children destructors. The child destructor
  37  * called after the parent would set the talloc_tos() to the wrong value.
  38  */
  39
  40 #include "includes.h"
  41
  42 struct talloc_stackframe {
  43         int talloc_stacksize;
  44         int talloc_stack_arraysize;
  45         TALLOC_CTX **talloc_stack;
  46 };
  47
  48 /*
  49  * In the single threaded case this is a pointer
  50  * to the global talloc_stackframe. In the MT-case
  51  * this is the pointer to the thread-specific key
  52  * used to look up the per-thread talloc_stackframe
  53  * pointer.
  54  */
  55
  56 static void *global_ts;
  57
  58 /* Variable to ensure TLS value is only initialized once. */
  59 static smb_thread_once_t ts_initialized = SMB_THREAD_ONCE_INIT;
  60
  61 static void talloc_stackframe_init(void * unused)
  62 {
  63         if (SMB_THREAD_CREATE_TLS("talloc_stackframe", global_ts)) {
  64                 smb_panic("talloc_stackframe_init create_tls failed");
  65         }
  66 }
  67
  68 static struct talloc_stackframe *talloc_stackframe_create(void)
  69 {
  70 #if defined(PARANOID_MALLOC_CHECKER)
  71 #ifdef calloc
  72 #undef calloc
  73 #endif
  74 #endif
  75         struct talloc_stackframe *ts = (struct talloc_stackframe *)calloc(
  76                 1, sizeof(struct talloc_stackframe));
  77 #if defined(PARANOID_MALLOC_CHECKER)
  78 #define calloc(n, s) __ERROR_DONT_USE_MALLOC_DIRECTLY
  79 #endif
  80
  81         if (!ts) {
  82                 smb_panic("talloc_stackframe_init malloc failed");
  83         }
  84
  85         SMB_THREAD_ONCE(&ts_initialized, talloc_stackframe_init, NULL);
  86
  87         if (SMB_THREAD_SET_TLS(global_ts, ts)) {
  88                 smb_panic("talloc_stackframe_init set_tls failed");
  89         }
  90         return ts;
  91 }
  92
  93 static int talloc_pop(TALLOC_CTX *frame)
  94 {
  95         struct talloc_stackframe *ts =
  96                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
  97         size_t blocks;
  98         int i;
  99
 100         /* Catch lazy frame-freeing. */
 101         if (ts->talloc_stack[ts->talloc_stacksize-1] != frame) {
 102                 DEBUG(0, ("Freed frame %s, expected %s.\n",
 103                           talloc_get_name(frame),
 104                           talloc_get_name(ts->talloc_stack
 105                                           [ts->talloc_stacksize-1])));
 106 #ifdef DEVELOPER
 107                 smb_panic("Frame not freed in order.");
 108 #endif
 109         }
 110
 111         for (i=0; i<10; i++) {
 112
 113                 /*
 114                  * We have to free our children first, calling all
 115                  * destructors. If a destructor hanging deeply off
 116                  * "frame" uses talloc_tos() itself while freeing the
 117                  * toplevel frame, we panic because that nested
 118                  * talloc_tos() in the destructor does not find a
 119                  * stackframe anymore.
 120                  *
 121                  * Do it in a loop up to 10 times as the destructors
 122                  * might use more of talloc_tos().
 123                  */
 124
 125                 talloc_free_children(frame);
 126
 127                 blocks = talloc_total_blocks(frame);
 128                 if (blocks == 1) {
 129                         break;
 130                 }
 131         }
 132
 133         if (blocks != 1) {
 134                 DBG_WARNING("Left %zu blocks after %i "
 135                             "talloc_free_children(frame) calls\n",
 136                             blocks, i);
 137         }
 138
 139         for (i=ts->talloc_stacksize-1; i>0; i--) {
 140                 if (frame == ts->talloc_stack[i]) {
 141                         break;
 142                 }
 143                 TALLOC_FREE(ts->talloc_stack[i]);
 144         }
 145
 146         ts->talloc_stack[i] = NULL;
 147         ts->talloc_stacksize = i;
 148         return 0;
 149 }
 150
 151 /*
 152  * Create a new talloc stack frame.
 153  *
 154  * When free'd, it frees all stack frames that were created after this one and
 155  * not explicitly freed.
 156  */
 157
 158 static TALLOC_CTX *talloc_stackframe_internal(const char *location,
 159                                               size_t poolsize)
 160 {
 161         TALLOC_CTX **tmp, *top;
 162         struct talloc_stackframe *ts =
 163                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 164
 165         if (ts == NULL) {
 166                 ts = talloc_stackframe_create();
 167         }
 168
 169         if (ts->talloc_stack_arraysize < ts->talloc_stacksize + 1) {
 170                 tmp = talloc_realloc(NULL, ts->talloc_stack, TALLOC_CTX *,
 171                                            ts->talloc_stacksize + 1);
 172                 if (tmp == NULL) {
 173                         goto fail;
 174                 }
 175                 ts->talloc_stack = tmp;
 176                 ts->talloc_stack_arraysize = ts->talloc_stacksize + 1;
 177         }
 178
 179         if (poolsize) {
 180                 top = talloc_pool(ts->talloc_stack, poolsize);
 181         } else {
 182                 TALLOC_CTX *parent;
 183                 /* We chain parentage, so if one is a pool we draw from it. */
 184                 if (ts->talloc_stacksize == 0) {
 185                         parent = ts->talloc_stack;
 186                 } else {
 187                         parent = ts->talloc_stack[ts->talloc_stacksize-1];
 188                 }
 189                 top = talloc_new(parent);
 190         }
 191
 192         if (top == NULL) {
 193                 goto fail;
 194         }
 195         talloc_set_name_const(top, location);
 196         talloc_set_destructor(top, talloc_pop);
 197
 198         ts->talloc_stack[ts->talloc_stacksize++] = top;
 199         return top;
 200
 201  fail:
 202         smb_panic("talloc_stackframe failed");
 203         return NULL;
 204 }
 205
 206 TALLOC_CTX *_talloc_stackframe(const char *location)
 207 {
 208         return talloc_stackframe_internal(location, 0);
 209 }
 210
 211 TALLOC_CTX *_talloc_stackframe_pool(const char *location, size_t poolsize)
 212 {
 213         return talloc_stackframe_internal(location, poolsize);
 214 }
 215
 216 /*
 217  * Get us the current top of the talloc stack.
 218  */
 219
 220 TALLOC_CTX *_talloc_tos(const char *location)
 221 {
 222         struct talloc_stackframe *ts =
 223                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 224
 225         if (ts == NULL || ts->talloc_stacksize == 0) {
 226                 _talloc_stackframe(location);
 227                 ts = (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 228                 DEBUG(0, ("no talloc stackframe at %s, leaking memory\n",
 229                           location));
 230 #ifdef DEVELOPER
 231                 smb_panic("No talloc stackframe");
 232 #endif
 233         }
 234
 235         return ts->talloc_stack[ts->talloc_stacksize-1];
 236 }
 237
 238 /*
 239  * return true if a talloc stackframe exists
 240  * this can be used to prevent memory leaks for code that can
 241  * optionally use a talloc stackframe (eg. nt_errstr())
 242  */
 243
 244 bool talloc_stackframe_exists(void)
 245 {
 246         struct talloc_stackframe *ts =
 247                 (struct talloc_stackframe *)SMB_THREAD_GET_TLS(global_ts);
 248
 249         if (ts == NULL || ts->talloc_stacksize == 0) {
 250                 return false;
 251         }
 252         return true;
 253 }