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Date: Thu, 16 May 2019 11:37:47 -0700 From: Yabin Cui <yabinc@...gle.com> To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org> Cc: linux-kernel@...r.kernel.org, Yabin Cui <yabinc@...gle.com> Subject: Re: [PATCH] perf/ring_buffer: Fix exposing a temporarily decreased data_head. >Indeed, good catch! Have you observed this, or is this patch due to code inspection? I observed this. I was using perf_event_open instead of linux tools perf to monitor a process continuously forking new processes, generating a lot of mmap records. And a sample record happens while generating a mmap record. For missing barriers, I thought local_xxx provided implied barriers. But I found atomic_ops.txt said not. Thanks for reminding! I will add them in path v2. I also think it's a good idea to use READ_ONCE/WRITE_ONCE for rb->nest. Will use it in patch v2.
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