19 Mar
2015
19 Mar
'15
6:30 p.m.
On Thu, Mar 19, 2015 at 01:39:58PM -0400, Steven Rostedt wrote:
+void printk_nmi_backtrace_complete(void) +{
- struct nmi_seq_buf *s;
- int len, cpu, i, last_i;
- /*
* Now that all the NMIs have triggered, we can dump out their* back traces safely to the console.*/- for_each_possible_cpu(cpu) {
s = &per_cpu(nmi_print_seq, cpu);last_i = 0;len = seq_buf_used(&s->seq);if (!len)continue;/* Print line by line. */for (i = 0; i < len; i++) {if (s->buffer[i] == '\n') {print_seq_line(s, last_i, i);last_i = i + 1;}}/* Check if there was a partial line. */if (last_i < len) {print_seq_line(s, last_i, len - 1);pr_cont("\n");}/* Wipe out the buffer ready for the next time around. */seq_buf_clear(&s->seq);- }
- clear_bit(0, &nmi_print_flag);
- smp_mb__after_atomic();
Is this really necessary. What is the mb synchronizing?
[ Added Peter Zijlstra to confirm it's not needed ]
It surely looks suspect; and it lacks a comment, which is a clear sign its buggy.
Now it if tries to order the accesses to the seqbuf againt the clearing of the bit one would have expected a _before_ barrier, not an _after_.