diff options
-rw-r--r-- | kernel/printk/printk.c | 35 |
1 files changed, 34 insertions, 1 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 8908142cbe3bda..c64f365a9896d8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -72,14 +72,47 @@ static int __init force_early_printk_setup(char *str) } early_param("force_early_printk", force_early_printk_setup); +static int early_printk_cpu = -1; + static int early_vprintk(const char *fmt, va_list args) { + int n, cpu, old; char buf[512]; - int n; + + cpu = get_cpu(); + /* + * Test-and-Set inter-cpu spinlock with recursion. + */ + for (;;) { + /* + * c-cas to avoid the exclusive bouncing on spin. + * Depends on the memory barrier implied by cmpxchg + * for ACQUIRE semantics. + */ + old = READ_ONCE(early_printk_cpu); + if (old == -1) { + old = cmpxchg(&early_printk_cpu, -1, cpu); + if (old == -1) + break; + } + /* + * Allow recursion for interrupts and the like. + */ + if (old == cpu) + break; + + cpu_relax(); + } n = vscnprintf(buf, sizeof(buf), fmt, args); early_console->write(early_console, buf, n); + /* + * Unlock -- in case @old == @cpu, this is a no-op. + */ + smp_store_release(&early_printk_cpu, old); + put_cpu(); + return n; } |