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authorStephane Eranian <eranian@google.com>2013-03-18 14:33:28 +0100
committerIngo Molnar <mingo@kernel.org>2013-03-21 12:04:35 +0100
commitdd9c086d9f507d02d5ba4d7c5eef4bb9518088b8 (patch)
tree581aba3f0c5417f9b6c25824e4364da82f731431 /README
parent0e48026ae7abf871e51eaa9183c81ab5bef4c267 (diff)
perf: Fix ring_buffer perf_output_space() boundary calculation
This patch fixes a flaw in perf_output_space(). In case the size of the space needed is bigger than the actual buffer size, there may be situations where the function would return true (i.e., there is space) when it should not. head > offset due to rounding of the masking logic. The problem can be tested by activating BTS on Intel processors. A BTS record can be as big as 16 pages. The following command fails: $ perf record -m 4 -c 1 -e branches:u my_test_program You will get a buffer corruption with this. Perf report won't be able to parse the perf.data. The fix is to first check that the requested space is smaller than the buffer size. If so, then the masking logic will work fine. If not, then there is no chance the record can be saved and it will be gracefully handled by upper code layers. [ In v2, we also make the logic for the writable more explicit by renaming it to rb->overwrite because it tells whether or not the buffer can overwrite its tail (suggested by PeterZ). ] Signed-off-by: Stephane Eranian <eranian@google.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: peterz@infradead.org Cc: jolsa@redhat.com Cc: fweisbec@gmail.com Link: http://lkml.kernel.org/r/20130318133327.GA3056@quad Signed-off-by: Ingo Molnar <mingo@kernel.org>
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