| Message ID | 20240411012904.237435058@goodmis.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | tracing: Persistent traces across a reboot or crash | expand |
On Wed, Apr 10, 2024 at 09:25:42PM -0400, Steven Rostedt wrote: > From: "Steven Rostedt (Google)" <rostedt@goodmis.org> > > In preparation for having the ring buffer mapped to a dedicated location, > which will have the same restrictions as user space memory mapped buffers, > allow it to use the "mapped" field of the ring_buffer_per_cpu structure > without having the user space meta page mapping. > > When this starts using the mapped field, it will need to handle adding a > user space mapping (and removing it) from a ring buffer that is using a > dedicated memory range. > > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org> > --- > kernel/trace/ring_buffer.c | 10 +++++++--- > 1 file changed, 7 insertions(+), 3 deletions(-) > > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c > index 793ecc454039..44b1d5f1a99a 100644 > --- a/kernel/trace/ring_buffer.c > +++ b/kernel/trace/ring_buffer.c > @@ -5223,6 +5223,9 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) > { > struct trace_buffer_meta *meta = cpu_buffer->meta_page; > > + if (!meta) > + return; > + > meta->reader.read = cpu_buffer->reader_page->read; > meta->reader.id = cpu_buffer->reader_page->id; > meta->reader.lost_events = cpu_buffer->lost_events; > @@ -6167,7 +6170,7 @@ rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu) > > mutex_lock(&cpu_buffer->mapping_lock); > > - if (!cpu_buffer->mapped) { > + if (!cpu_buffer->mapped || !cpu_buffer->meta_page) { > mutex_unlock(&cpu_buffer->mapping_lock); > return ERR_PTR(-ENODEV); > } > @@ -6345,12 +6348,13 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu, IIUC, we still allow to map from user-space this buffer. So we now can have mapped && !meta_page. Then the "if (cpu_buffer->mapped) {" that skips the meta_page creation in ring_buffer_map() should be replaced by if (cpu_buffer->meta_page). > */ > raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); > rb_setup_ids_meta_page(cpu_buffer, subbuf_ids); > + > raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); > > err = __rb_map_vma(cpu_buffer, vma); > if (!err) { > raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); > - cpu_buffer->mapped = 1; > + cpu_buffer->mapped++; > raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); > } else { > kfree(cpu_buffer->subbuf_ids); > @@ -6388,7 +6392,7 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int cpu) > mutex_lock(&buffer->mutex); > raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); In this function, there's also a check for cpu_buffer->mapped > 1. This avoids killing the meta-page while someone is still in use. It seems like a dedicated meta_page counter will be necessary. Otherwise, in the event of a ring-buffer mapped at boot we, would setup the meta-page on the first mmap() and never tear it down. > > - cpu_buffer->mapped = 0; > + cpu_buffer->mapped--; > > raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); > > -- > 2.43.0 > >
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 793ecc454039..44b1d5f1a99a 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -5223,6 +5223,9 @@ static void rb_update_meta_page(struct ring_buffer_per_cpu *cpu_buffer) { struct trace_buffer_meta *meta = cpu_buffer->meta_page; + if (!meta) + return; + meta->reader.read = cpu_buffer->reader_page->read; meta->reader.id = cpu_buffer->reader_page->id; meta->reader.lost_events = cpu_buffer->lost_events; @@ -6167,7 +6170,7 @@ rb_get_mapped_buffer(struct trace_buffer *buffer, int cpu) mutex_lock(&cpu_buffer->mapping_lock); - if (!cpu_buffer->mapped) { + if (!cpu_buffer->mapped || !cpu_buffer->meta_page) { mutex_unlock(&cpu_buffer->mapping_lock); return ERR_PTR(-ENODEV); } @@ -6345,12 +6348,13 @@ int ring_buffer_map(struct trace_buffer *buffer, int cpu, */ raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); rb_setup_ids_meta_page(cpu_buffer, subbuf_ids); + raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); err = __rb_map_vma(cpu_buffer, vma); if (!err) { raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); - cpu_buffer->mapped = 1; + cpu_buffer->mapped++; raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags); } else { kfree(cpu_buffer->subbuf_ids); @@ -6388,7 +6392,7 @@ int ring_buffer_unmap(struct trace_buffer *buffer, int cpu) mutex_lock(&buffer->mutex); raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags); - cpu_buffer->mapped = 0; + cpu_buffer->mapped--; raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);