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>
721f0dfc3c