Messages in this thread | | | Subject | Re: [PATCH] tracing: consolidate protection of reader access to the ring buffer | From | Steven Rostedt <> | Date | Wed, 06 Jan 2010 10:28:07 -0500 |
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On Wed, 2010-01-06 at 20:08 +0800, Lai Jiangshan wrote: > At the beginning, access to the ring buffer are fully serialized > by trace_types_lock. Patch d7350c3f4569 gives more freedom to readers, > and patch b04cc6b1f6 adds code to protect trace_pipe and cpu#/trace_pipe. > > But actually it is not enough, ring buffer readers are not always > read-only, they may consume data. > > This patch makes accesses to trace, trace_pipe, trace_pipe_raw > cpu#/trace, cpu#/trace_pipe and cpu#/trace_pipe_raw are serialized. > And removes tracing_reader_cpumask which is used to protect trace_pipe. > > detail: > > ring buffer serializes readers, but it is low level protection. > The validity of the events (which returns by ring_buffer_peek() ..etc) > are not protected by ring buffer. > > The content of events may become garbage if we allow other process consumes > these events concurrently: > A) the page of the consumed events may become a normal page > (not reader page) in ring buffer, and this page will be rewrited > by events producer. > B) The page of the consumed events may become a page for splice_read, > and this page will be returned to system. > > This patch adds trace_access_lock() and trace_access_unlock() primitives. > > These primitives allow multi process access to different cpu ring buffer > concurrently. > > These primitives don't distinguish read-only and read-consume access. > Multi read-only access are also serialized. > > And we don't use these primitives when we open files, > we only use them when we read files. > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
I queue this up with your other pending patches for .34
Thanks!
-- Steve
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