On 15/07/15 21:39, Russell King wrote:
+void nmi_trigger_all_cpu_backtrace(bool include_self,
+ void (*raise)(cpumask_t *mask))
+{
+ struct nmi_seq_buf *s;
+ int i, cpu, this_cpu = get_cpu();
+
+ if (test_and_set_bit(0, &backtrace_flag)) {
+ /*
+ * If there is already a trigger_all_cpu_backtrace() in progress
+ * (backtrace_flag == 1), don't output double cpu dump infos.
+ */
+ put_cpu();
+ return;
+ }
+
+ cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
+ if (!include_self)
+ cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
+
+ cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask));
+
+ /*
+ * Set up per_cpu seq_buf buffers that the NMIs running on the other
+ * CPUs will write to.
+ */
+ for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
+ s = &per_cpu(nmi_print_seq, cpu);
+ seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
+ }
+
+ if (!cpumask_empty(to_cpumask(backtrace_mask))) {
+ pr_info("Sending NMI to %s CPUs:\n",
+ (include_self ? "all" : "other"));
+ raise(to_cpumask(backtrace_mask));
On ARM, this code could be running with IRQs locked and with raise()
implemented using IRQs. In such as case the IPI will not be raised until
the function exists (and perhaps never). Thanks to the timeout we will
exit but we end up needlessly failing to print a backtrace for the
calling CPU.
The solution I used for this was to special case the current CPU and
call nmi_cpu_backtrace() directly. Originally I made this logic arm only
but I can't really see any reason for this to be arch specific so the
logic to do that should probably be included here.
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