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__perf_session__process_pipe_events reuses the same memory buffer to process all events in the pipe. When reordering is needed (e.g. -b option), events are not immediately flushed, but kept around until reordering is possible, causing memory corruption. The problem is usually observed by a "Unknown sample error" output. It can easily be reproduced by: perf record -o - noploop | perf inject -b > output Committer testing: Before: $ perf record -o - stress -t 2 -c 2 | perf inject -b > /dev/null stress: info: [8297] dispatching hogs: 2 cpu, 0 io, 0 vm, 0 hdd stress: info: [8297] successful run completed in 2s [ perf record: Woken up 3 times to write data ] [ perf record: Captured and wrote 0.000 MB - ] Warning: Found 1 unknown events! Is this an older tool processing a perf.data file generated by a more recent tool? If that is not the case, consider reporting to linux-kernel@vger.kernel.org. $ After: $ perf record -o - stress -t 2 -c 2 | perf inject -b > /dev/null stress: info: [9027] dispatching hogs: 2 cpu, 0 io, 0 vm, 0 hdd stress: info: [9027] successful run completed in 2s [ perf record: Woken up 3 times to write data ] [ perf record: Captured and wrote 0.000 MB - ] no symbols found in /usr/bin/stress, maybe install a debug package? no symbols found in /usr/bin/stress, maybe install a debug package? $ Signed-off-by: David Carrillo-Cisneros <davidcc@google.com> Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com> Acked-by: Jiri Olsa <jolsa@kernel.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Andi Kleen <ak@linux.intel.com> Cc: He Kuang <hekuang@huawei.com> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Paul Turner <pjt@google.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Simon Que <sque@chromium.org> Cc: Stephane Eranian <eranian@google.com> Cc: Wang Nan <wangnan0@huawei.com> Link: http://lkml.kernel.org/r/20170410201432.24807-3-davidcc@google.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> |
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| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.