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Jaroslav reported errors from valgrind over perf python script: # echo 0 > /sys/devices/system/cpu/cpu4/online # valgrind ./test.py ==7524== Memcheck, a memory error detector ... ==7524== Command: ./test.py ==7524== pid 7526 exited ==7524== Invalid read of size 8 ==7524== at 0xCC2C2B3: perf_mmap__read_forward (evlist.c:780) ==7524== by 0xCC2A681: pyrf_evlist__read_on_cpu (python.c:959) ... ==7524== Address 0x65c4868 is 16 bytes after a block of size 459,36.. ==7524== at 0x4C2B955: calloc (vg_replace_malloc.c:711) ==7524== by 0xCC2F484: zalloc (util.h:35) ==7524== by 0xCC2F484: perf_evlist__alloc_mmap (evlist.c:978) ... The reason for this is in the python interface, that allows a script to pass arbitrary cpu number, which is then used to access struct perf_evlist::mmap array. That's obviously wrong and works only when if all cpus are available and fails if some cpu is missing, like in the example above. This patch makes pyrf_evlist__read_on_cpu() search the evlist's maps array for the proper map to access. It's linear search at the moment. Based on the way how is the read_on_cpu used, I don't think we need to be fast in here. But we could add some hash in the middle to make it fast/er. We don't allow python interface to set write_backward event attribute, so it's safe to check only evlist's mmaps. Reported-by: Jaroslav Škarvada <jskarvad@redhat.com> Signed-off-by: Jiri Olsa <jolsa@kernel.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: David Ahern <dsahern@gmail.com> Cc: Joe Mario <jmario@redhat.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20180817114556.28000-3-jolsa@kernel.org Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
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.