check_preempt.c

   1 /*
   2  * Copyright (C) 2018 Oracle.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
  16  */
  17
  18 /*
  19  * This code works with check_preempt_info.c.  The info.c file records
  20  * return_states (this code handles caller_info states).  The main
  21  * thing that this code does is it provides get_preempt_count() function
  22  * the check_scheduling_in_atomic.c file.
  23  *
  24  * The preempt count is a counter and when it's non-zero then we are not
  25  * allowed to call schedule().
  26  *
  27  * If we're called with a lock held then we say that preempt is one.  (In
  28  * real life, it could be higher but this is easier to program).  So if
  29  * any caller is holding the lock we have preempt = 1.
  30  *
  31  * If during the course of parsing the call, the preempt count gets out of
  32  * sync on one side of a branch statement, then we assume the lower preempt
  33  * count is correct.  (In other words, we choose to miss some bugs rather
  34  * than add false postives).
  35  */
  36
  37 #include "smatch.h"
  38 #include "smatch_slist.h"
  39
  40 static int my_id;
  41
  42 int get_preempt_cnt(void)
  43 {
  44         struct smatch_state *state;
  45
  46         state = get_state(my_id, "preempt", NULL);
  47         if (!state)
  48                 return 0;
  49         return PTR_INT(state->data);
  50 }
  51
  52 void clear_preempt_cnt(void)
  53 {
  54         struct smatch_state *state;
  55
  56         state = get_state(my_id, "preempt", NULL);
  57         if (!state || PTR_INT(state->data) == 0)
  58                 return;
  59         set_state(my_id, "preempt", NULL, alloc_state_num(0));
  60 }
  61
  62 static unsigned long fn_decrements_preempt;
  63 bool function_decrements_preempt(void)
  64 {
  65         return fn_decrements_preempt;
  66 }
  67
  68 static int get_start_preempt_cnt(void)
  69 {
  70         struct stree *orig, *start;
  71         int ret;
  72
  73         start = get_start_states();
  74         orig = __swap_cur_stree(start);
  75
  76         ret = get_preempt_cnt();
  77
  78         __swap_cur_stree(orig);
  79         return ret;
  80 }
  81
  82 static bool passes_MSG_DONTWAIT(struct expression *expr)
  83 {
  84         struct expression *arg;
  85         char *macro;
  86
  87         FOR_EACH_PTR(expr->args, arg) {
  88                 macro = get_macro_name(arg->pos);
  89                 if (macro && strcmp(macro, "MSG_DONTWAIT") == 0)
  90                         return true;
  91         } END_FOR_EACH_PTR(arg);
  92
  93         return false;
  94 }
  95
  96 static bool is_no_preempt_caller(void)
  97 {
  98         char *fn = get_function();
  99
 100         if (!fn)
 101                 return false;
 102         if (strcmp(fn, "sg_miter_next") == 0)
 103                 return true;
 104         return false;
 105 }
 106
 107 static void match_call_info(struct expression *expr)
 108 {
 109         int start_cnt, cnt;
 110         int param;
 111         const char *disables = "";
 112
 113         if (is_fn_ptr(expr->fn))
 114                 return;
 115         cnt = get_preempt_cnt();
 116         if (cnt <= 0)
 117                 return;
 118         if (passes_MSG_DONTWAIT(expr))
 119                 return;
 120         if (is_no_preempt_caller())
 121                 return;
 122         start_cnt = get_start_preempt_cnt();
 123         if (start_cnt < cnt)
 124                 disables = "<- disables preempt";
 125
 126         param = get_gfp_param(expr);
 127         if (param >= 0)
 128                 return;
 129         sql_insert_caller_info(expr, PREEMPT_ADD, -1, "", disables);
 130 }
 131
 132 static struct smatch_state *merge_func(struct smatch_state *s1, struct smatch_state *s2)
 133 {
 134         if (__in_function_def) {
 135                 if (PTR_INT(s1->data) > PTR_INT(s2->data))
 136                         return s1;
 137                 return s2;
 138         }
 139         if (PTR_INT(s1->data) < PTR_INT(s2->data))
 140                 return s1;
 141         return s2;
 142 }
 143
 144 static void select_call_info(const char *name, struct symbol *sym, char *key, char *value)
 145 {
 146         set_state(my_id, "preempt", NULL, alloc_state_num(1));
 147 }
 148
 149 void __preempt_add(void)
 150 {
 151         set_state(my_id, "preempt", NULL, alloc_state_num(get_preempt_cnt() + 1));
 152 }
 153
 154 void __preempt_sub(void)
 155 {
 156         fn_decrements_preempt = 1;
 157         set_state(my_id, "preempt", NULL, alloc_state_num(get_preempt_cnt() - 1));
 158 }
 159
 160 static void match_preempt_count_zero(const char *fn, struct expression *call_expr,
 161                                      struct expression *assign_expr, void *_param)
 162 {
 163         set_state(my_id, "preempt", NULL, alloc_state_num(0));
 164 }
 165
 166 static void match_preempt_count_non_zero(const char *fn, struct expression *call_expr,
 167                                          struct expression *assign_expr, void *_param)
 168 {
 169         struct sm_state *sm, *tmp;
 170         bool possibly_atomic = false;
 171
 172         sm = get_sm_state(my_id, "preempt", NULL);
 173         if (!sm)
 174                 return;
 175
 176         FOR_EACH_PTR(sm->possible, tmp) {
 177                 if (tmp->state->data) {
 178                         possibly_atomic = true;
 179                         break;
 180                 }
 181         } END_FOR_EACH_PTR(tmp);
 182
 183         if (!possibly_atomic)
 184                 return;
 185
 186         set_state(my_id, "preempt", NULL, alloc_state_num(1));
 187 }
 188
 189 void check_preempt(int id)
 190 {
 191         my_id = id;
 192
 193         if (option_project != PROJ_KERNEL)
 194                 return;
 195
 196         add_function_data(&fn_decrements_preempt);
 197         set_dynamic_states(my_id);
 198         add_merge_hook(my_id, &merge_func);
 199
 200         return_implies_exact("preempt_count", int_zero, int_zero, &match_preempt_count_zero, NULL);
 201         return_implies_exact("preempt_count", int_one, int_max, &match_preempt_count_non_zero, NULL);
 202
 203         select_caller_info_hook(&select_call_info, PREEMPT_ADD);
 204         add_hook(&match_call_info, FUNCTION_CALL_HOOK);
 205 }
 206