On Wed, 16 Jul 2014 10:58:04 +0200
Petr Mladek <pmla...@suse.cz> wrote:
> +/**
> + * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
> + * @buffer_a: One buffer to swap with
> + * @buffer_b: The other buffer to swap with
> + *
> + * This function is useful for tracers that want to take a "snapshot"
> + * of a CPU buffer and has another back up buffer lying around.
> + * It is expected that the tracer handles the cpu buffer not being
> + * used at the moment.
> + */
> +int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
> + struct ring_buffer *buffer_b, int cpu)
> +{
> + struct ring_buffer_swap_info rb_swap_info = {
> + .buffer_a = buffer_a,
> + .buffer_b = buffer_b,
> + };
> + int ret;
> +
> + /*
> + * Swap the CPU buffer on the same CPU. Recording has to be fast
> + * and and this helps to avoid memory barriers.
> + */
> + ret = smp_call_function_single(cpu, ring_buffer_swap_this_cpu,
> + (void *)&rb_swap_info, 1);
> + if (ret)
> + return ret;
> +
> + return rb_swap_info.ret;
We need to check if the cpu is on the current CPU and if so, just call
the function directly. Otherwise this can't be done from interrupt
disabled context.
Enable IRQSOFF_TRACER and FTRACE_STARTUP_TEST to see why.
[ 2.098008] Testing tracer irqsoff:
[ 2.351020] ------------[ cut here ]------------
[ 2.352000] WARNING: CPU: 3 PID: 0 at
/home/rostedt/work/git/linux-trace.git/kernel/smp.c:283
smp_call_function_single+0x66/0xad()
[ 2.352000] Modules linked in:
[ 2.352000] CPU: 3 PID: 0 Comm: swapper/3 Not tainted 3.16.0-rc3-test+ #93
[ 2.352000] Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To
be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007
[ 2.352000] 0000000000000000 ffffffff810058cb ffffffff81503d20
0000000000000000
[ 2.352000] ffffffff81040ca1 0000000000000000 ffffffff8109712f
0000000000000001
[ 2.352000] 0000000000000003 ffffffff810bf9db ffff88007a3c3e30
0000000000000001
[ 2.352000] Call Trace:
[ 2.352000] [<ffffffff810058cb>] ? show_stack+0x5/0x3e
[ 2.352000] [<ffffffff81503d20>] ? dump_stack+0x4a/0x75
[ 2.352000] [<ffffffff81040ca1>] ? warn_slowpath_common+0x7e/0x97
[ 2.352000] [<ffffffff8109712f>] ? smp_call_function_single+0x66/0xad
[ 2.352000] [<ffffffff810bf9db>] ? ring_buffer_swap_cpu+0x45/0x45
[ 2.352000] [<ffffffff8109712f>] ? smp_call_function_single+0x66/0xad
[ 2.352000] [<ffffffff810970ce>] ? smp_call_function_single+0x5/0xad
[ 2.352000] [<ffffffff810bf9ce>] ? ring_buffer_swap_cpu+0x38/0x45
[ 2.352000] [<ffffffff810c6c64>] ? update_max_tr_single+0xb6/0x11f
[ 2.352000] [<ffffffff8100ae3e>] ? default_idle+0x1d/0x30
[ 2.352000] [<ffffffff810cd2ac>] ? stop_critical_timing+0x139/0x20d
[ 2.352000] [<ffffffff8100ae3e>] ? default_idle+0x1d/0x30
[ 2.352000] [<ffffffff81072d35>] ? cpu_startup_entry+0x115/0x220
[ 2.352000] [<ffffffff81027610>] ? start_secondary+0x21c/0x222
[ 2.352000] ---[ end trace a712676a9f9a53a0 ]---
-- Steve
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