1 /**
 2  * dump_stack - dump the current task information and its stack trace
 3  *
 4  * Architectures can override this implementation by implementing its own.
 5  */
 6 #ifdef CONFIG_SMP
 7 static atomic_t dump_lock = ATOMIC_INIT(-1);
 8 
 9 asmlinkage __visible void dump_stack(void)
10 {
11     unsigned long flags;
12     int was_locked;
13     int old;
14     int cpu;
15 
16     /*
17      * Permit this cpu to perform nested stack dumps while serialising
18      * against other CPUs
19      */
20 retry:
21     local_irq_save(flags);
22     cpu = smp_processor_id();
23     old = atomic_cmpxchg(&dump_lock, -1, cpu);
24     if (old == -1) {
25         was_locked = 0;
26     } else if (old == cpu) {
27         was_locked = 1;
28     } else {
29         local_irq_restore(flags);
30         /*
31          * Wait for the lock to release before jumping to
32          * atomic_cmpxchg() in order to mitigate the thundering herd
33          * problem.
34          */
35         do { cpu_relax(); } while (atomic_read(&dump_lock) != -1);
36         goto retry;
37     }
38 
39     __dump_stack();
40 
41     if (!was_locked)
42         atomic_set(&dump_lock, -1);
43 
44     local_irq_restore(flags);
45 }
46 #else
47 asmlinkage __visible void dump_stack(void)
48 {
49     __dump_stack();
50 }
51 #endif