In preparation for the introduction of a panic handler for trace remotes, add a ring_buffer_read_remote_meta_page(). This is basically similar to ring_buffer_poll_remote, but it doesn't try to wake-up readers and, in the !RING_BUFFER_ALL_CPUS case, uses panic-friendly locks.
While at it, update trace_remote_has_cpu() to use this new function instead of ring_buffer_poll_remote(), avoiding unnecessary wakeups when verifying if a CPU buffer is active. Finally, the distracted engineer who wrote that ring_buffer_poll_remote() forgot to document it. Add a kerneldoc for that function too. Signed-off-by: Vincent Donnefort <[email protected]> diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index 994f52b34344..6e008a548063 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -298,6 +298,7 @@ struct ring_buffer_remote { void *priv; }; +int ring_buffer_read_remote_meta_page(struct trace_buffer *buffer, int cpu); int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu); struct trace_buffer * diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 7b07d2004cc6..88ac346c65ec 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -6623,6 +6623,59 @@ bool ring_buffer_empty_cpu(struct trace_buffer *buffer, int cpu) } EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu); +/** + * ring_buffer_read_remote_meta_page - read the meta page of a remote ring buffer + * @buffer: The ring buffer + * @cpu: The CPU buffer to read (or RING_BUFFER_ALL_CPUS) + * + * Returns: + * 0 on success, or -EINVAL if the CPU is not in the buffer's cpumask. + */ +int ring_buffer_read_remote_meta_page(struct trace_buffer *buffer, int cpu) +{ + struct ring_buffer_per_cpu *cpu_buffer; + + if (cpu != RING_BUFFER_ALL_CPUS) { + unsigned long flags; + bool dolock; + + if (!cpumask_test_cpu(cpu, buffer->cpumask)) + return -EINVAL; + + cpu_buffer = buffer->buffers[cpu]; + + local_irq_save(flags); + dolock = rb_reader_lock(cpu_buffer); + rb_read_remote_meta_page(cpu_buffer); + rb_reader_unlock(cpu_buffer, dolock); + local_irq_restore(flags); + return 0; + } + + guard(cpus_read_lock)(); + + for_each_buffer_cpu(buffer, cpu) { + cpu_buffer = buffer->buffers[cpu]; + + guard(raw_spinlock)(&cpu_buffer->reader_lock); + rb_read_remote_meta_page(cpu_buffer); + } + + return 0; +} + +/** + * ring_buffer_poll_remote - poll a remote ring buffer for new data + * @buffer: The ring buffer + * @cpu: The CPU buffer to poll (or RING_BUFFER_ALL_CPUS) + * + * This function polls the specified remote CPU buffer (or all of them) + * by reading its meta page to update the local reader's view. If new + * entries are detected, it triggers wakeups for any waiting readers. + * + * Returns: + * 0 on success, or -EINVAL if the CPU is not in the buffer's cpumask. + */ int ring_buffer_poll_remote(struct trace_buffer *buffer, int cpu) { struct ring_buffer_per_cpu *cpu_buffer; diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c index 1bf0ba159c92..e708dcd7d258 100644 --- a/kernel/trace/trace_remote.c +++ b/kernel/trace/trace_remote.c @@ -291,7 +291,7 @@ 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; + return ring_buffer_read_remote_meta_page(remote->trace_buffer, cpu) == 0; } static void __free_ring_buffer_iter(struct trace_remote_iterator *iter, int cpu) -- 2.54.0.1032.g2f8565e1d1-goog
