sched/debug: Show the registers of 'current' in dump_cpu_task()
The dump_cpu_task() function does not print registers on architectures that do not support NMIs. However, registers can be useful for debugging. Fortunately, in the case where dump_cpu_task() is invoked from an interrupt handler and is dumping the current CPU's stack, the get_irq_regs() function can be used to get the registers. Therefore, this commit makes dump_cpu_task() check to see if it is being asked to dump the current CPU's stack from within an interrupt handler, and, if so, it uses the get_irq_regs() function to obtain the registers. On systems that do support NMIs, this commit has the further advantage of avoiding a self-NMI in this case. This is an example of rcu self-detected stall on arm64, which does not support NMIs: [ 27.501721] rcu: INFO: rcu_preempt self-detected stall on CPU [ 27.502238] rcu: 0-....: (1250 ticks this GP) idle=4f7/1/0x4000000000000000 softirq=2594/2594 fqs=619 [ 27.502632] (t=1251 jiffies g=2989 q=29 ncpus=4) [ 27.503845] CPU: 0 PID: 306 Comm: test0 Not tainted 5.19.0-rc7-00009-g1c1a6c29ff99-dirty #46 [ 27.504732] Hardware name: linux,dummy-virt (DT) [ 27.504947] pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 27.504998] pc : arch_counter_read+0x18/0x24 [ 27.505301] lr : arch_counter_read+0x18/0x24 [ 27.505328] sp : ffff80000b29bdf0 [ 27.505345] x29: ffff80000b29bdf0 x28: 0000000000000000 x27: 0000000000000000 [ 27.505475] x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000 [ 27.505553] x23: 0000000000001f40 x22: ffff800009849c48 x21: 000000065f871ae0 [ 27.505627] x20: 00000000000025ec x19: ffff80000a6eb300 x18: ffffffffffffffff [ 27.505654] x17: 0000000000000001 x16: 0000000000000000 x15: ffff80000a6d0296 [ 27.505681] x14: ffffffffffffffff x13: ffff80000a29bc18 x12: 0000000000000426 [ 27.505709] x11: 0000000000000162 x10: ffff80000a2f3c18 x9 : ffff80000a29bc18 [ 27.505736] x8 : 00000000ffffefff x7 : ffff80000a2f3c18 x6 : 00000000759bd013 [ 27.505761] x5 : 01ffffffffffffff x4 : 0002dc6c00000000 x3 : 0000000000000017 [ 27.505787] x2 : 00000000000025ec x1 : ffff80000b29bdf0 x0 : 0000000075a30653 [ 27.505937] Call trace: [ 27.506002] arch_counter_read+0x18/0x24 [ 27.506171] ktime_get+0x48/0xa0 [ 27.506207] test_task+0x70/0xf0 [ 27.506227] kthread+0x10c/0x110 [ 27.506243] ret_from_fork+0x10/0x20 This is a marked improvement over the old output: [ 27.944550] rcu: INFO: rcu_preempt self-detected stall on CPU [ 27.944980] rcu: 0-....: (1249 ticks this GP) idle=cbb/1/0x4000000000000000 softirq=2610/2610 fqs=614 [ 27.945407] (t=1251 jiffies g=2681 q=28 ncpus=4) [ 27.945731] Task dump for CPU 0: [ 27.945844] task:test0 state:R running task stack: 0 pid: 306 ppid: 2 flags:0x0000000a [ 27.946073] Call trace: [ 27.946151] dump_backtrace.part.0+0xc8/0xd4 [ 27.946378] show_stack+0x18/0x70 [ 27.946405] sched_show_task+0x150/0x180 [ 27.946427] dump_cpu_task+0x44/0x54 [ 27.947193] rcu_dump_cpu_stacks+0xec/0x130 [ 27.947212] rcu_sched_clock_irq+0xb18/0xef0 [ 27.947231] update_process_times+0x68/0xac [ 27.947248] tick_sched_handle+0x34/0x60 [ 27.947266] tick_sched_timer+0x4c/0xa4 [ 27.947281] __hrtimer_run_queues+0x178/0x360 [ 27.947295] hrtimer_interrupt+0xe8/0x244 [ 27.947309] arch_timer_handler_virt+0x38/0x4c [ 27.947326] handle_percpu_devid_irq+0x88/0x230 [ 27.947342] generic_handle_domain_irq+0x2c/0x44 [ 27.947357] gic_handle_irq+0x44/0xc4 [ 27.947376] call_on_irq_stack+0x2c/0x54 [ 27.947415] do_interrupt_handler+0x80/0x94 [ 27.947431] el1_interrupt+0x34/0x70 [ 27.947447] el1h_64_irq_handler+0x18/0x24 [ 27.947462] el1h_64_irq+0x64/0x68 <--- the above backtrace is worthless [ 27.947474] arch_counter_read+0x18/0x24 [ 27.947487] ktime_get+0x48/0xa0 [ 27.947501] test_task+0x70/0xf0 [ 27.947520] kthread+0x10c/0x110 [ 27.947538] ret_from_fork+0x10/0x20 Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Ben Segall <bsegall@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Valentin Schneider <vschneid@redhat.com>
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