xtensa: SMP: fix secondary CPU initialization

- add missing memory barriers to the secondary CPU synchronization spin
  loops; add comment to the matching memory barrier in the boot_secondary
  and __cpu_die functions;
- use READ_ONCE/WRITE_ONCE to access cpu_start_id/cpu_start_ccount
  instead of reading/writing them directly;
- re-initialize cpu_running every time before starting secondary CPU to
  flush possible previous CPU startup results.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

diff --git a/arch/xtensa/kernel/head.S b/arch/xtensa/kernel/head.S
index da08e75..7f00971 100644 (file)
--- a/arch/xtensa/kernel/head.S
+++ b/arch/xtensa/kernel/head.S
@@ -276,12 +276,13 @@ should_never_return:
 
        movi    a2, cpu_start_ccount
 1:
+       memw
        l32i    a3, a2, 0
        beqi    a3, 0, 1b
        movi    a3, 0
        s32i    a3, a2, 0
-       memw
 1:
+       memw
        l32i    a3, a2, 0
        beqi    a3, 0, 1b
        wsr     a3, ccount
@@ -317,11 +318,13 @@ ENTRY(cpu_restart)
        rsr     a0, prid
        neg     a2, a0
        movi    a3, cpu_start_id
+       memw
        s32i    a2, a3, 0
 #if XCHAL_DCACHE_IS_WRITEBACK
        dhwbi   a3, 0
 #endif
 1:
+       memw
        l32i    a2, a3, 0
        dhi     a3, 0
        bne     a2, a0, 1b

diff --git a/arch/xtensa/kernel/smp.c b/arch/xtensa/kernel/smp.c
index 932d646..c9fc2c4 100644 (file)
--- a/arch/xtensa/kernel/smp.c
+++ b/arch/xtensa/kernel/smp.c
@@ -195,9 +195,11 @@ static int boot_secondary(unsigned int cpu, struct task_struct *ts)
        int i;
 
 #ifdef CONFIG_HOTPLUG_CPU
-       cpu_start_id = cpu;
-       system_flush_invalidate_dcache_range(
-                       (unsigned long)&cpu_start_id, sizeof(cpu_start_id));
+       WRITE_ONCE(cpu_start_id, cpu);
+       /* Pairs with the third memw in the cpu_restart */
+       mb();
+       system_flush_invalidate_dcache_range((unsigned long)&cpu_start_id,
+                                            sizeof(cpu_start_id));
 #endif
        smp_call_function_single(0, mx_cpu_start, (void *)cpu, 1);
 
@@ -206,18 +208,21 @@ static int boot_secondary(unsigned int cpu, struct task_struct *ts)
                        ccount = get_ccount();
                while (!ccount);
 
-               cpu_start_ccount = ccount;
+               WRITE_ONCE(cpu_start_ccount, ccount);
 
-               while (time_before(jiffies, timeout)) {
+               do {
+                       /*
+                        * Pairs with the first two memws in the
+                        * .Lboot_secondary.
+                        */
                        mb();
-                       if (!cpu_start_ccount)
-                               break;
-               }
+                       ccount = READ_ONCE(cpu_start_ccount);
+               } while (ccount && time_before(jiffies, timeout));
 
-               if (cpu_start_ccount) {
+               if (ccount) {
                        smp_call_function_single(0, mx_cpu_stop,
-                                       (void *)cpu, 1);
-                       cpu_start_ccount = 0;
+                                                (void *)cpu, 1);
+                       WRITE_ONCE(cpu_start_ccount, 0);
                        return -EIO;
                }
        }
@@ -237,6 +242,7 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
        pr_debug("%s: Calling wakeup_secondary(cpu:%d, idle:%p, sp: %08lx)\n",
                        __func__, cpu, idle, start_info.stack);
 
+       init_completion(&cpu_running);
        ret = boot_secondary(cpu, idle);
        if (ret == 0) {
                wait_for_completion_timeout(&cpu_running,
@@ -298,8 +304,10 @@ void __cpu_die(unsigned int cpu)
        unsigned long timeout = jiffies + msecs_to_jiffies(1000);
        while (time_before(jiffies, timeout)) {
                system_invalidate_dcache_range((unsigned long)&cpu_start_id,
-                               sizeof(cpu_start_id));
-               if (cpu_start_id == -cpu) {
+                                              sizeof(cpu_start_id));
+               /* Pairs with the second memw in the cpu_restart */
+               mb();
+               if (READ_ONCE(cpu_start_id) == -cpu) {
                        platform_cpu_kill(cpu);
                        return;
                }