From: "Steven Rostedt (Google)" rostedt@goodmis.org
For the ring buffer iterator (non-consuming read), the event needs to be copied into the iterator buffer to make sure that a writer does not overwrite it while the user is reading it. If a write happens during the copy, the buffer is simply discarded.
But the temp buffer itself was not big enough. The allocation of the buffer was only BUF_MAX_DATA_SIZE, which is the maximum data size that can be passed into the ring buffer and saved. But the temp buffer needs to hold the meta data as well. That would be BUF_PAGE_SIZE and not BUF_MAX_DATA_SIZE.
Link: https://lore.kernel.org/linux-trace-kernel/20231212072558.61f76493@gandalf.l...
Cc: stable@vger.kernel.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mark Rutland mark.rutland@arm.com Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Fixes: 785888c544e04 ("ring-buffer: Have rb_iter_head_event() handle concurrent writer") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org --- kernel/trace/ring_buffer.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index c7abcc215fe2..1d9caee7f542 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2409,7 +2409,7 @@ rb_iter_head_event(struct ring_buffer_iter *iter) */ barrier();
- if ((iter->head + length) > commit || length > BUF_MAX_DATA_SIZE) + if ((iter->head + length) > commit || length > BUF_PAGE_SIZE) /* Writer corrupted the read? */ goto reset;
@@ -5118,7 +5118,8 @@ ring_buffer_read_prepare(struct trace_buffer *buffer, int cpu, gfp_t flags) if (!iter) return NULL;
- iter->event = kmalloc(BUF_MAX_DATA_SIZE, flags); + /* Holds the entire event: data and meta data */ + iter->event = kmalloc(BUF_PAGE_SIZE, flags); if (!iter->event) { kfree(iter); return NULL;