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rarely ever hit, and requires the user to do something that users rarely do. It took a few special test cases to even trigger this bug, and one of them was just one test in the process of finishing up as another one started. Both bugs have to do with the ring buffer iterator rb_iter_peek(), but one is more indirect than the other. The fist bug fix is simply an increase in the safety net loop counter. The counter makes sure that the rb_iter_peek() only iterates the number of times we expect it can, and no more. Well, there was one way it could iterate one more than we expected, and that caused the ring buffer to shutdown with a nasty warning. The fix was simply to up that counter by one. The other bug has to be with rb_iter_reset() (called by rb_iter_peek()). This happens when a user reads both the trace_pipe and trace files. The trace_pipe is a consuming read and does not use the ring buffer iterator, but the trace file is not a consuming read and does use the ring buffer iterator. When the trace file is being read, if it detects that a consuming read occurred, it resets the iterator and starts over. But the reset code that does this (rb_iter_reset()), checks if the reader_page is linked to the ring buffer or not, and will look into the ring buffer itself if it is not. This is wrong, as it should always try to read the reader page first. Not to mention, the code that looked into the ring buffer did it wrong, and used the header_page "read" offset to start reading on that page. That offset is bogus for pages in the writable ring buffer, and was corrupting the iterator, and it would start returning bogus events. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAABAgAGBQJT44tRAAoJEKQekfcNnQGuMVIH/3evbjKT+w6Kon4S0LfLSejl YDsXYkeO/lGiO3MnUveqq1jfw2+yHtyBVUipvfG0A61urMUhyUvjveph8Ec2cQ4Q qHl0J28vDfF5tpKiYzygRN01wHD6GXYh+XZSChkA4ItzzD8K51lsZT1Yd+I2pTy2 DgH01EEEYiwYJcih+T4vlbKqYju6pwgxqKNCTv0RdVXUPya/tG9X2Nf8VGQTbmKS FIO73qObYR+P9iXGIuPfyOxk2EvBiWS15WownZmfhZZxOIKx9IrDYwTsiV1+AJw+ sJFER1ulobYGDtGDa9yyrNJQr6wgbrfCDELnNKmdLUTlSwgZjLXpE2HEmlelY/s= =5mQl -----END PGP SIGNATURE----- Merge tag 'trace-fixes-3.16' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace Pull trace file read iterator fixes from Steven Rostedt: "This contains a fix for two long standing bugs. Both of which are rarely ever hit, and requires the user to do something that users rarely do. It took a few special test cases to even trigger this bug, and one of them was just one test in the process of finishing up as another one started. Both bugs have to do with the ring buffer iterator rb_iter_peek(), but one is more indirect than the other. The fist bug fix is simply an increase in the safety net loop counter. The counter makes sure that the rb_iter_peek() only iterates the number of times we expect it can, and no more. Well, there was one way it could iterate one more than we expected, and that caused the ring buffer to shutdown with a nasty warning. The fix was simply to up that counter by one. The other bug has to be with rb_iter_reset() (called by rb_iter_peek()). This happens when a user reads both the trace_pipe and trace files. The trace_pipe is a consuming read and does not use the ring buffer iterator, but the trace file is not a consuming read and does use the ring buffer iterator. When the trace file is being read, if it detects that a consuming read occurred, it resets the iterator and starts over. But the reset code that does this (rb_iter_reset()), checks if the reader_page is linked to the ring buffer or not, and will look into the ring buffer itself if it is not. This is wrong, as it should always try to read the reader page first. Not to mention, the code that looked into the ring buffer did it wrong, and used the header_page "read" offset to start reading on that page. That offset is bogus for pages in the writable ring buffer, and was corrupting the iterator, and it would start returning bogus events" * tag 'trace-fixes-3.16' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: ring-buffer: Always reset iterator to reader page ring-buffer: Up rb_iter_peek() loop count to 3 |
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|---|---|---|
| .. | ||
| blktrace.c | ||
| ftrace.c | ||
| Kconfig | ||
| Makefile | ||
| power-traces.c | ||
| ring_buffer_benchmark.c | ||
| ring_buffer.c | ||
| rpm-traces.c | ||
| trace_benchmark.c | ||
| trace_benchmark.h | ||
| trace_branch.c | ||
| trace_clock.c | ||
| trace_entries.h | ||
| trace_event_perf.c | ||
| trace_events_filter_test.h | ||
| trace_events_filter.c | ||
| trace_events_trigger.c | ||
| trace_events.c | ||
| trace_export.c | ||
| trace_functions_graph.c | ||
| trace_functions.c | ||
| trace_irqsoff.c | ||
| trace_kdb.c | ||
| trace_kprobe.c | ||
| trace_mmiotrace.c | ||
| trace_nop.c | ||
| trace_output.c | ||
| trace_output.h | ||
| trace_printk.c | ||
| trace_probe.c | ||
| trace_probe.h | ||
| trace_sched_switch.c | ||
| trace_sched_wakeup.c | ||
| trace_selftest_dynamic.c | ||
| trace_selftest.c | ||
| trace_seq.c | ||
| trace_stack.c | ||
| trace_stat.c | ||
| trace_stat.h | ||
| trace_syscalls.c | ||
| trace_uprobe.c | ||
| trace.c | ||
| trace.h | ||