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mipsxx_pmu_handle_shared_irq() calls irq_work_run() while holding the pmuint_rwlock for read. irq_work_run() can, via perf_pending_event(), call try_to_wake_up() which can try to take rq->lock. However, perf can also call perf_pmu_enable() (and thus take the pmuint_rwlock for write) while holding the rq->lock, from finish_task_switch() via perf_event_context_sched_in(). This leads to an ABBA deadlock: PID: 3855 TASK: 8f7ce288 CPU: 2 COMMAND: "process" #0 [89c39ac8] __delay at 803b5be4 #1 [89c39ac8] do_raw_spin_lock at 8008fdcc #2 [89c39af8] try_to_wake_up at 8006e47c #3 [89c39b38] pollwake at 8018eab0 #4 [89c39b68] __wake_up_common at 800879f4 #5 [89c39b98] __wake_up at 800880e4 #6 [89c39bc8] perf_event_wakeup at 8012109c #7 [89c39be8] perf_pending_event at 80121184 #8 [89c39c08] irq_work_run_list at 801151f0 #9 [89c39c38] irq_work_run at 80115274 #10 [89c39c50] mipsxx_pmu_handle_shared_irq at 8002cc7c PID: 1481 TASK: 8eaac6a8 CPU: 3 COMMAND: "process" #0 [8de7f900] do_raw_write_lock at 800900e0 #1 [8de7f918] perf_event_context_sched_in at 80122310 #2 [8de7f938] __perf_event_task_sched_in at 80122608 #3 [8de7f958] finish_task_switch at 8006b8a4 #4 [8de7f998] __schedule at 805e4dc4 #5 [8de7f9f8] schedule at 805e5558 #6 [8de7fa10] schedule_hrtimeout_range_clock at 805e9984 #7 [8de7fa70] poll_schedule_timeout at 8018e8f8 #8 [8de7fa88] do_select at 8018f338 #9 [8de7fd88] core_sys_select at 8018f5cc #10 [8de7fee0] sys_select at 8018f854 #11 [8de7ff28] syscall_common at 80028fc8 The lock seems to be there to protect the hardware counters so there is no need to hold it across irq_work_run(). Signed-off-by: Rabin Vincent <rabinv@axis.com> Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.