On Thu, Dec 12 2024 at 19:19, David Woodhouse wrote: > On Thu, 2024-12-12 at 19:04 +0100, Thomas Gleixner wrote: > Build current master (231825b2e1ff here). The config I'm using is at > http://david.woodhou.se/config-x86-kjump-irqs although I don't think > there's anything special other than CONFIG_KEXEC_JUMP and enough > lockdep to trigger the complaints. > > I've been running in qemu with the test case shoved into an initrd for > faster testing, but it works just as well done manually. If it matters, > the QEMU command line on my Haswell box is > > qemu-system-x86_64 -accel kvm,kernel-irqchip=split -display none \ > -serial mon:stdio -kernel arch/x86/boot/bzImage -smp 2 -m 2g \ > -append "console=ttyS0 root=/dev/vda1 no_console_suspend earlyprintk=serial" \ > -drive file=/var/lib/libvirt/images/fedora.qcow2,if=virtio \ > -cpu host --no-reboot -nic user,model=virtio > > Probably the only important part of that is the no_console_suspend. I misread that and somehow thought it does _not_ happen with no_console_suspend. Duh! So that made it reproduce and after adding some more lockdep hacks here is the culprit: [ 15.177945] DEBUG_LOCKS_WARN_ON(suspend_syscore_active) [ 15.178980] CPU: 0 UID: 0 PID: 410 Comm: k.1 Not tainted 6.13.0-rc2+ #118 [ 15.185613] Call Trace: [ 15.185760] <TASK> [ 15.187678] __cond_resched+0x21/0x60 [ 15.187923] down_timeout+0x18/0x60 [ 15.188159] acpi_os_wait_semaphore+0x4c/0x80 [ 15.188424] acpi_ut_acquire_mutex+0x3d/0x100 [ 15.188665] acpi_ns_get_node+0x27/0x60 [ 15.188879] acpi_ns_evaluate+0x1cb/0x2d0 [ 15.189106] acpi_rs_set_srs_method_data+0x156/0x190 [ 15.189382] acpi_pci_link_set+0x11c/0x290 [ 15.189618] irqrouter_resume+0x54/0x60 [ 15.189826] syscore_resume+0x6a/0x200 [ 15.190033] kernel_kexec+0x145/0x1c0 [ 15.190239] __do_sys_reboot+0xeb/0x240 [ 15.190561] do_syscall_64+0x95/0x180 This is a long standing problem, which probably got more visible with the recent printk changes. Something does a wakeup and the scheduler sets the NEED_RESCHED flag. cond_resched() sees it set and invokes schedule() from a completely bogus context. Nothing knowns about the current system state and therefore happily assumes that everything is cool and shiny. I also found that kexec jump fails to set system_state = SYSTEM_SUSPEND before syscore_suspend() and back to SYSTEM_RUNNING after syscore_resume(). See suspend/hibernate... But setting this does not solve the problem because NEED_RESCHED still gets set and cond_resched() is oblivious of the state. Quite some of the code paths in syscore_suspend()/resume() can result in triggering a wakeup with the exactly same consequences. They might not have done so yet, but as they share a lot of code with normal operation it's just a question of time. And of course then you need a code path which is invoked after that, which actually invokes cond_resched(). Adding more debug, there are indeed a couple of ways to set NEED_RESCHED between invoking syscore_suspend() and returning from syscore_resume(). Some stuff schedules work [un]conditonally. So the real question is how to deal with the general problem, which obviously affects suspend as well. The only thing I came up with so far is the hack below. It cures the problem for PREEMPT_NONE and PREEMPT_VOLUNTARY. PREEMPT_FULL is not affected because preemptible() checks whether the preemption count is zero and interrupts are enabled and cond_resched() not active. We could check for interrupts enabled in cond_resched() too, but that's not pretty either. With that applied the problem goes away, but after a lot of repetitions of the reproducer in a tight loop the whole machinery stops dead: [ 29.913179] Disabling non-boot CPUs ... [ 29.930328] smpboot: CPU 1 is now offline [ 29.930593] crash hp: kexec_trylock() failed, kdump image may be inaccurate B[ 29.940588] Enabling non-boot CPUs ... [ 29.940856] crash hp: kexec_trylock() failed, kdump image may be inaccurate [ 29.941242] smpboot: Booting Node 0 Processor 1 APIC 0x1 [ 29.942654] CPU1 is up [ 29.945856] virtio_blk virtio1: 2/0/0 default/read/poll queues [ 29.948556] OOM killer enabled. [ 29.948750] Restarting tasks ... done. Success [ 29.960044] Freezing user space processes [ 29.961447] Freezing user space processes completed (elapsed 0.001 seconds) [ 29.961861] OOM killer disabled. [ 30.102485] ata2: found unknown device (class 0) [ 30.107387] Disabling non-boot CPUs ... That happens without 'no_console_suspend' on the command line as well, but that's for tomorrow ... Thanks, tglx --- --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -1025,6 +1025,7 @@ int kernel_kexec(void) if (error) goto Enable_cpus; local_irq_disable(); + system_state = SYSTEM_SUSPEND; error = syscore_suspend(); if (error) goto Enable_irqs; @@ -1054,6 +1055,7 @@ int kernel_kexec(void) if (kexec_image->preserve_context) { syscore_resume(); Enable_irqs: + system_state = SYSTEM_RUNNING; local_irq_enable(); Enable_cpus: suspend_enable_secondary_cpus(); --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7276,7 +7276,7 @@ void rt_mutex_setprio(struct task_struct #if !defined(CONFIG_PREEMPTION) || defined(CONFIG_PREEMPT_DYNAMIC) int __sched __cond_resched(void) { - if (should_resched(0)) { + if (should_resched(0) && system_state != SYSTEM_SUSPEND) { preempt_schedule_common(); return 1; }
