On Mon, 11 Oct 2021 at 17:11, Andrea Righi <andrea.righi@xxxxxxxxxxxxx> wrote: > > On Mon, Oct 11, 2021 at 05:00:15PM +0200, Dmitry Vyukov wrote: > > On Mon, 11 Oct 2021 at 16:42, Andrea Righi <andrea.righi@xxxxxxxxxxxxx> wrote: > > > > > > On Mon, Oct 11, 2021 at 12:03:52PM +0200, Marco Elver wrote: > > > > On Mon, 11 Oct 2021 at 11:53, Andrea Righi <andrea.righi@xxxxxxxxxxxxx> wrote: > > > > > On Mon, Oct 11, 2021 at 11:23:32AM +0200, Andrea Righi wrote: > > > > > ... > > > > > > > You seem to use the default 20s stall timeout. FWIW syzbot uses 160 > > > > > > > secs timeout for TCG emulation to avoid false positive warnings: > > > > > > > https://github.com/google/syzkaller/blob/838e7e2cd9228583ca33c49a39aea4d863d3e36d/dashboard/config/linux/upstream-arm64-kasan.config#L509 > > > > > > > There are a number of other timeouts raised as well, some as high as > > > > > > > 420 seconds. > > > > > > > > > > > > I see, I'll try with these settings and see if I can still hit the soft > > > > > > lockup messages. > > > > > > > > > > Still getting soft lockup messages even with the new timeout settings: > > > > > > > > > > [ 462.663766] watchdog: BUG: soft lockup - CPU#2 stuck for 430s! [systemd-udevd:168] > > > > > [ 462.755758] watchdog: BUG: soft lockup - CPU#3 stuck for 430s! [systemd-udevd:171] > > > > > [ 924.663765] watchdog: BUG: soft lockup - CPU#2 stuck for 861s! [systemd-udevd:168] > > > > > [ 924.755767] watchdog: BUG: soft lockup - CPU#3 stuck for 861s! [systemd-udevd:171] > > > > > > > > The lockups are expected if you're hitting the TCG bug I linked. Try > > > > to pass '-enable-kvm' to the inner qemu instance (my bad if you > > > > already have), assuming that's somehow easy to do. > > > > > > If I add '-enable-kvm' I can triggering other random panics (almost > > > immediately), like this one for example: > > > > > > [21383.189976] BUG: kernel NULL pointer dereference, address: 0000000000000098 > > > [21383.190633] #PF: supervisor read access in kernel mode > > > [21383.191072] #PF: error_code(0x0000) - not-present page > > > [21383.191529] PGD 0 P4D 0 > > > [21383.191771] Oops: 0000 [#1] SMP NOPTI > > > [21383.192113] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.15-rc4 > > > [21383.192757] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014 > > > [21383.193414] RIP: 0010:wb_timer_fn+0x44/0x3c0 > > > [21383.193855] Code: 41 8b 9c 24 98 00 00 00 41 8b 94 24 b8 00 00 00 41 8b 84 24 d8 00 00 00 4d 8b 74 24 28 01 d3 01 c3 49 8b 44 24 60 48 8b 40 78 <4c> 8b b8 98 00 00 00 4d 85 f6 0f 84 c4 00 00 00 49 83 7c 24 30 00 > > > [21383.195366] RSP: 0018:ffffbcd140003e68 EFLAGS: 00010246 > > > [21383.195842] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000004 > > > [21383.196425] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff9a3521f4fd80 > > > [21383.197010] RBP: ffffbcd140003e90 R08: 0000000000000000 R09: 0000000000000000 > > > [21383.197594] R10: 0000000000000004 R11: 000000000000000f R12: ffff9a34c75c4900 > > > [21383.198178] R13: ffff9a34c3906de0 R14: 0000000000000000 R15: ffff9a353dc18c00 > > > [21383.198763] FS: 0000000000000000(0000) GS:ffff9a353dc00000(0000) knlGS:0000000000000000 > > > [21383.199558] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > > [21383.200212] CR2: 0000000000000098 CR3: 0000000005f54000 CR4: 00000000000006f0 > > > [21383.200930] Call Trace: > > > [21383.201210] <IRQ> > > > [21383.201461] ? blk_stat_free_callback_rcu+0x30/0x30 > > > [21383.202692] blk_stat_timer_fn+0x138/0x140 > > > [21383.203180] call_timer_fn+0x2b/0x100 > > > [21383.203666] __run_timers.part.0+0x1d1/0x240 > > > [21383.204227] ? kvm_clock_get_cycles+0x11/0x20 > > > [21383.204815] ? ktime_get+0x3e/0xa0 > > > [21383.205309] ? native_apic_msr_write+0x2c/0x30 > > > [21383.205914] ? lapic_next_event+0x20/0x30 > > > [21383.206412] ? clockevents_program_event+0x94/0xf0 > > > [21383.206873] run_timer_softirq+0x2a/0x50 > > > [21383.207260] __do_softirq+0xcb/0x26f > > > [21383.207647] irq_exit_rcu+0x8c/0xb0 > > > [21383.208010] sysvec_apic_timer_interrupt+0x7c/0x90 > > > [21383.208464] </IRQ> > > > [21383.208713] asm_sysvec_apic_timer_interrupt+0x12/0x20 > > > > > > I think that systemd autotest used to use -enable-kvm, but then they > > > removed it, because it was introducing too many problems in the nested > > > KVM context. I'm not sure about the nature of those problems though, I > > > can investigate a bit and see if I can understand what they were > > > exactly. > > > > This looks like just a plain bug in wb_timer_fn, not something related > > to virtualization. > > Do you have this fix? > > https://syzkaller.appspot.com/bug?extid=aa0801b6b32dca9dda82 > > Yes, it looks like I have this: > > d152c682f03c block: add an explicit ->disk backpointer to the request_queue Then there is another bug in wb_timer_fn I guess... Don't know if this is the same or something else: https://lore.kernel.org/lkml/CAHbLzkrdGva2dzO36r62LKv_ip5trbMK0BO3vCeSBk2_7OE-zA@xxxxxxxxxxxxxx/ There also were some data races in this function: https://groups.google.com/g/syzkaller-upstream-moderation/search?q=wb_timer_fn
