When a trace_buffer is created while a CPU is offline, this CPU is cleared from the trace_buffer CPU mask, preventing the creation of a non-consuming iterator (ring_buffer_iter). For trace remotes, it means the iterator fails to be allocated (-ENOMEM) even though there are available ring buffers in the trace_buffer.
For non-consuming reads of trace remotes, skip missing ring_buffer_iter to allow reading the available ring buffers. Signed-off-by: Vincent Donnefort <[email protected]> diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 0d78e5f5fe98..d6c3f94d67cd 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -282,6 +282,14 @@ static void trace_remote_put(struct trace_remote *remote) trace_remote_try_unload(remote); } +static bool trace_remote_has_cpu(struct trace_remote *remote, int cpu) +{ + if (cpu == RING_BUFFER_ALL_CPUS) + return true; + + return ring_buffer_poll_remote(remote->trace_buffer, cpu) == 0; +} + static void __poll_remote(struct work_struct *work) { struct delayed_work *dwork = to_delayed_work(work); @@ -324,6 +332,10 @@ static int __alloc_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu) iter->rb_iters[cpu] = ring_buffer_read_start(iter->remote->trace_buffer, cpu, GFP_KERNEL); if (!iter->rb_iters[cpu]) { + /* This CPU isn't part of trace_buffer. Skip it */ + if (!trace_remote_has_cpu(iter->remote, cpu)) + continue; + __free_ring_buffer_iter(iter, RING_BUFFER_ALL_CPUS); return -ENOMEM; } @@ -347,10 +359,10 @@ static struct trace_remote_iterator if (ret) return ERR_PTR(ret); - /* Test the CPU */ - ret = ring_buffer_poll_remote(remote->trace_buffer, cpu); - if (ret) + if (!trace_remote_has_cpu(remote, cpu)) { + ret = -ENODEV; goto err; + } iter = kzalloc_obj(*iter); if (iter) { @@ -361,6 +373,7 @@ static struct trace_remote_iterator switch (type) { case TRI_CONSUMING: + ring_buffer_poll_remote(remote->trace_buffer, cpu); INIT_DELAYED_WORK(&iter->poll_work, __poll_remote); schedule_delayed_work(&iter->poll_work, msecs_to_jiffies(remote->poll_ms)); break; @@ -476,6 +489,9 @@ __peek_event(struct trace_remote_iterator *iter, int cpu, u64 *ts, unsigned long return ring_buffer_peek(iter->remote->trace_buffer, cpu, ts, lost_events); case TRI_NONCONSUMING: rb_iter = __get_rb_iter(iter, cpu); + if (!rb_iter) + return NULL; + rb_evt = ring_buffer_iter_peek(rb_iter, ts); if (!rb_evt) return NULL; -- 2.53.0.1118.gaef5881109-goog
