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Sam bobroff
96d0161086
Correct the DSCR SPR becoming temporarily corrupted if a task is context switched during a transaction. The problem occurs while suspending the task and is caused by saving the DSCR to thread.dscr after it has already been set to the CPU's default value: __switch_to() calls __switch_to_tm() which calls tm_reclaim_task() which calls tm_reclaim_thread() which calls tm_reclaim() where the DSCR is set to the CPU's default __switch_to() calls _switch() where thread.dscr is set to the DSCR When the task is resumed, it's transaction will be doomed (as usual) and the DSCR SPR will be corrupted, although the checkpointed value will be correct. Therefore the DSCR will be immediately corrected by the transaction aborting, unless it has been suspended. In that case the incorrect value can be seen by the task until it resumes the transaction. The fix is to treat the DSCR similarly to the TAR and save it early in __switch_to(). A program exposing the problem is added to the kernel self tests as: tools/testing/selftests/powerpc/tm/tm-resched-dscr. Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com> CC: <stable@vger.kernel.org> [v3.10+] Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Linux Kernel Selftests The kernel contains a set of "self tests" under the tools/testing/selftests/ directory. These are intended to be small unit tests to exercise individual code paths in the kernel. Running the selftests ===================== To build the tests: $ make -C tools/testing/selftests To run the tests: $ make -C tools/testing/selftests run_tests - note that some tests will require root privileges. To run only tests targetted for a single subsystem: $ make -C tools/testing/selftests TARGETS=cpu-hotplug run_tests See the top-level tools/testing/selftests/Makefile for the list of all possible targets. Contributing new tests ====================== In general, the rules for for selftests are * Do as much as you can if you're not root; * Don't take too long; * Don't break the build on any architecture, and * Don't cause the top-level "make run_tests" to fail if your feature is unconfigured.