Messages in this thread Patch in this message | | | Date | Tue, 14 Apr 2020 10:05:02 +0300 | From | Leon Romanovsky <> | Subject | Re: [PATCH] x86/apic: Fix circular locking dependency between console and hrtimer locks |
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On Tue, Apr 14, 2020 at 08:24:54AM +0200, Ingo Molnar wrote: > > * Leon Romanovsky <leon@kernel.org> wrote: > > > Hi, > > > > Any feedback? > > https://lore.kernel.org/lkml/20200407170925.1775019-1-leon@kernel.org/ > > The fix definitely looks legit, lockdep is right that we shouldn't take > the console_sem.lock even under trylock. > > It's only a printk_once(), yet I'm wondering why in the last ~8 years > this never triggered. Nobody ever ran lockdep and debug console level > enabled on such hardware, or did something else change? > > One possibility would be that apic_check_deadline_errata() marked almost > all Intel systems as broken and the TSC-deadline hardware never actually > got activated. In that case you have triggered rarely tested code and > might see other weirdnesses. Just saying. :-)
It is hard to say what was changed, but after -rc1, we started to see those lockdep splats almost in every run.
But if we are talking about other weirdnesses, I have another splat in my QEMU machine, which is different, but from the same code area.
[ 1.383968] ACPI: Added _OSI(Module Device) [ 1.385684] ACPI: Added _OSI(Processor Device) [ 1.389345] ACPI: Added _OSI(3.0 _SCP Extensions) [ 1.389345] ACPI: Added _OSI(Processor Aggregator Device) [ 1.393454] ACPI: Added _OSI(Linux-Dell-Video) [ 1.394920] ACPI: Added _OSI(Linux-Lenovo-NV-HDMI-Audio) [ 1.396481] ACPI: Added _OSI(Linux-HPI-Hybrid-Graphics) [ 1.793418] ACPI: 1 ACPI AML tables successfully acquired and loaded [ 1.845452] [ 1.846768] ============================= [ 1.849293] [ BUG: Invalid wait context ] [ 1.849293] 5.7.0-rc1+ #1229 Not tainted [ 1.849293] ----------------------------- [ 1.849293] swapper/1/0 is trying to lock: [ 1.849293] ffff88806c8a4418 (&n->list_lock){-...}-{3:3}, at: deactivate_slab.isra.0+0x304/0x6d0 [ 1.849293] other info that might help us debug this: [ 1.849293] context-{2:2} [ 1.849293] 1 lock held by swapper/1/0: [ 1.849293] #0: ffffffff826cb000 (rcu_callback){....}-{0:0}, at: rcu_core+0x317/0x9e0 [ 1.849293] stack backtrace: [ 1.849293] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.7.0-rc1+ #1229 [ 1.849293] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 0 4/01/2014 [ 1.849293] Call Trace: [ 1.849293] <IRQ> [ 1.849293] dump_stack+0x97/0xe0 [ 1.849293] __lock_acquire.cold+0xd6/0x354 [ 1.849293] ? sched_clock_cpu+0x11f/0x140 [ 1.849293] ? mark_held_locks+0x90/0x90 [ 1.849293] ? __lock_acquire+0x8bf/0x3800 [ 1.849293] lock_acquire+0x155/0x4f0 [ 1.849293] ? deactivate_slab.isra.0+0x304/0x6d0 [ 1.849293] ? lock_release+0x660/0x660 [ 1.849293] ? sched_clock_local+0x99/0xc0 [ 1.849293] ? sched_clock_cpu+0x11f/0x140 [ 1.849293] _raw_spin_lock+0x31/0x80 [ 1.849293] ? deactivate_slab.isra.0+0x304/0x6d0 [ 1.849293] deactivate_slab.isra.0+0x304/0x6d0 [ 1.849293] ? pvclock_clocksource_read+0xd9/0x190 [ 1.849293] ? slub_cpu_dead+0xd0/0xd0 [ 1.849293] flush_cpu_slab+0x36/0x50 [ 1.849293] flush_smp_call_function_queue+0xc2/0x1e0 [ 1.849293] smp_call_function_interrupt+0x93/0x2f0 [ 1.849293] call_function_interrupt+0xf/0x20 [ 1.849293] RIP: 0010:quarantine_put+0xba/0x150 [ 1.849293] Code: e8 bb bb ec ff 48 8b 44 24 18 65 48 33 04 25 28 00 00 00 0f 85 a0 00 00 00 48 83 c4 20 5b 5d 41 5 c c3 e8 39 b8 ec ff 41 54 9d <eb> d9 48 89 e6 e8 cc fe ff ff 48 c7 c7 60 e3 76 82 e8 c0 f3 6b 00 [ 1.849293] RSP: 0000:ffff88806d209db0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff03 [ 1.849293] RAX: 0000000000000000 RBX: ffff88806be33658 RCX: dffffc0000000000 [ 1.849293] RDX: 0000000000000007 RSI: 0000000000000002 RDI: ffff88806cb5876c [ 1.849293] RBP: ffff88806c80de00 R08: ffffffff811656ed R09: 0000000000000000 [ 1.849293] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000246 [ 1.849293] R13: ffff88806c80de00 R14: 0000000000000206 R15: 0000000000000000 [ 1.849293] ? call_function_interrupt+0xa/0x20 [ 1.849293] ? lockdep_hardirqs_on+0x17d/0x270 [ 1.849293] __kasan_slab_free+0x144/0x180 [ 1.849293] ? rcu_core+0x35c/0x9e0 [ 1.849293] kmem_cache_free+0xc6/0x370 [ 1.849293] ? migrate_pages+0xa70/0xa70 [ 1.849293] rcu_core+0x35c/0x9e0 [ 1.849293] ? rcu_core+0x317/0x9e0 [ 1.849293] ? rcu_note_context_switch+0x300/0x300 [ 1.849293] ? rcu_read_lock_sched_held+0xa1/0xd0 [ 1.849293] ? rcu_read_lock_bh_held+0xb0/0xb0 [ 1.849293] ? run_rebalance_domains+0x11d/0x140 [ 1.849293] __do_softirq+0x11c/0x612 [ 1.849293] ? rcu_read_lock_bh_held+0xb0/0xb0 [ 1.849293] irq_exit+0xfb/0x100 [ 1.849293] smp_apic_timer_interrupt+0x12e/0x360 [ 1.849293] apic_timer_interrupt+0xf/0x20 [ 1.849293] </IRQ> [ 1.849293] RIP: 0010:default_idle+0x6e/0x250 [ 1.849293] Code: c7 c7 40 11 01 83 e8 f1 ec 93 ff 48 c7 c7 40 11 01 83 e8 b5 0c 94 ff 8b 05 6f a8 5f 01 85 c0 7e 0 7 0f 00 2d 84 f4 5f 00 fb f4 <be> 04 00 00 00 48 c7 c7 c8 bc 98 82 65 8b 2d 4f 48 60 7e e8 ba ec [ 1.849293] RSP: 0000:ffff88806cb67dc8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13 [ 1.849293] RAX: 0000000000000000 RBX: ffff88806cb58000 RCX: dffffc0000000000 [ 1.849293] RDX: 0000000000000003 RSI: 0000000000000004 RDI: ffffffff83011140 [ 1.849293] RBP: 0000000000000001 R08: ffffffff81a168cb R09: fffffbfff0602229 [ 1.849293] R10: 0000000000000003 R11: fffffbfff0602228 R12: ffffffff829a13f0 [ 1.849293] R13: 0000000000000000 R14: ffff88806cb58000 R15: 0000000000000000 [ 1.849293] ? default_idle+0x5b/0x250 [ 1.849293] ? default_idle+0x5b/0x250 [ 1.849293] do_idle+0x321/0x380 [ 1.849293] ? arch_cpu_idle_exit+0x40/0x40 [ 1.849293] ? mark_held_locks+0x1d/0x90 [ 1.849293] ? _raw_spin_unlock_irqrestore+0x3e/0x50 [ 1.849293] cpu_startup_entry+0x19/0x20 [ 1.849293] start_secondary+0x214/0x280 [ 1.849293] ? set_cpu_sibling_map+0x9e0/0x9e0 [ 1.849293] secondary_startup_64+0xa4/0xb0 [ 2.093362] ACPI: Interpreter enabled
> > Or a bootup with "debug" specified is much more rare in production > systems, hence the 8 years old bug. > > > > It is far away from my main expertise and I'm not sure that the solution > > > is correct, but it definitely fixed our regression. > > > --- > > > arch/x86/kernel/apic/apic.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c > > > index d254cebdd3c3..6706b2cd9aec 100644 > > > --- a/arch/x86/kernel/apic/apic.c > > > +++ b/arch/x86/kernel/apic/apic.c > > > @@ -353,7 +353,7 @@ static void __setup_APIC_LVTT(unsigned int clocks, int oneshot, int irqen) > > > */ > > > asm volatile("mfence" : : : "memory"); > > > > > > - printk_once(KERN_DEBUG "TSC deadline timer enabled\n"); > > > + printk_deferred_once(KERN_DEBUG "TSC deadline timer enabled\n"); > > I think we should move this essentially initialization-time message much > earlier during bootup, when we are not holding any hrtimer locks. > > One good place would be apic_check_deadline_errata(). This place: > > if (boot_cpu_data.microcode >= rev) > return; > > setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER); > pr_err(FW_BUG "TSC_DEADLINE disabled due to Errata; " > "please update microcode to version: 0x%x (or later)\n", rev); > > Could be something like: > > if (boot_cpu_data.microcode >= rev) { > pr_debug("x86/apic: TSC deadline timer enabled.\n"); > return; > } > > setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER); > pr_err(FW_BUG "TSC_DEADLINE disabled due to CPU errata, please update microcode to version: 0x%x (or later)\n", rev);
I don't know what is x2apic_mode, but won't x2apic_mode == 1 prevent from setting timer? If yes, we will print "enabled" message too early.
2091 void __init init_apic_mappings(void) <...> 2095 apic_check_deadline_errata(); 2096 2097 if (x2apic_mode) { 2098 boot_cpu_physical_apicid = read_apic_id(); 2099 return; 2100 }
> > (Note the small fixes I did to the errata message - we should do that and > also move all user-facing messages into a single line while at it.) > > Thanks, > > Ingo
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