Re: [printk] INFO: possible circular locking dependency detected

From: Jan Kara
Date: Fri Aug 01 2014 - 06:35:02 EST

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Hello,

On Fri 01-08-14 09:26:38, Wu Fengguang wrote:
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> commit 939f04bec1a4ef6ba4370b0f34b01decc844b1b1
> Author: Jan Kara <jack@xxxxxxx>
> AuthorDate: Wed Jun 4 16:11:37 2014 -0700
> Commit: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> CommitDate: Wed Jun 4 16:54:17 2014 -0700
>
> printk: enable interrupts before calling console_trylock_for_printk()
>
> We need interrupts disabled when calling console_trylock_for_printk()
> only so that cpu id we pass to can_use_console() remains valid (for
> other things console_sem provides all the exclusion we need and
> deadlocks on console_sem due to interrupts are impossible because we use
> down_trylock()). However if we are rescheduled, we are guaranteed to
> run on an online cpu so we can easily just get the cpu id in
> can_use_console().
>
> We can lose a bit of performance when we enable interrupts in
> vprintk_emit() and then disable them again in console_unlock() but OTOH
> it can somewhat reduce interrupt latency caused by console_unlock()
> especially since later in the patch series we will want to spin on
> console_sem in console_trylock_for_printk().
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Thanks for report! Two notes here:
1) This commit has been reverted from upstream already because machines
with lockdep enabled were unable to boot in some cases (lockdep decided
to report problem and hung the machine while doing it).
2) This patch just makes the problem visible.

In this particular case I think the problem is in
clockevents_increase_min_delta(). It is calling printk() from under
hrtimer_bases.lock and that is causing lock inversion with some scheduler
locks.

The attached patch should fix the problem. Can you please test it (but you
cannot use latest Linus' kernel as that has
939f04bec1a4ef6ba4370b0f34b01decc844b1b1 reverted)?

Honza

> +----------------------------------------------------+------------+------------+------------+
> | | bd8d7cf5b8 | 939f04bec1 | fb3ec67942 |
> +----------------------------------------------------+------------+------------+------------+
> | boot_successes | 1159 | 280 | 41 |
> | boot_failures | 41 | 20 | 5 |
> | BUG:kernel_boot_hang | 41 | 13 | 3 |
> | INFO:possible_circular_locking_dependency_detected | 0 | 7 | 2 |
> | backtrace:do_fork | 0 | 7 | 2 |
> | backtrace:vfs_write | 0 | 7 | 2 |
> | backtrace:SyS_write | 0 | 7 | 2 |
> | backtrace:event_create_dir | 0 | 2 | 1 |
> | backtrace:event_trace_init | 0 | 2 | 1 |
> | backtrace:kernel_init_freeable | 0 | 3 | 1 |
> | backtrace:SYSC_perf_event_open | 0 | 7 | 2 |
> | backtrace:SyS_perf_event_open | 0 | 7 | 2 |
> | backtrace:trace_create_cpu_file | 0 | 1 | |
> | backtrace:init_tracer_debugfs | 0 | 1 | |
> | backtrace:tracer_init_debugfs | 0 | 1 | |
> +----------------------------------------------------+------------+------------+------------+
>
> [ 29.644027] CE: hpet increased min_delta_ns to 25312 nsec
> [ 29.644027]
> [ 29.644027] ======================================================
> [ 29.644027] [ INFO: possible circular locking dependency detected ]
> [ 29.644027] 3.15.0-rc8-06195-g939f04b #2 Not tainted
> [ 29.644027] -------------------------------------------------------
> [ 29.644027] trinity-main/74 is trying to acquire lock:
> [ 29.644027] (&port_lock_key){-.....}, at: [<811c60be>] serial8250_console_write+0x8c/0x10c
> [ 29.644027]
> [ 29.644027] but task is already holding lock:
> [ 29.644027] (hrtimer_bases.lock){-.-...}, at: [<8103caeb>] hrtimer_try_to_cancel+0x13/0x66
> [ 29.644027]
> [ 29.644027] which lock already depends on the new lock.
> [ 29.644027]
> [ 29.644027]
> [ 29.644027] the existing dependency chain (in reverse order) is:
> [ 29.644027]
> [ 29.644027] -> #5 (hrtimer_bases.lock){-.-...}:
> [ 29.644027] [<8104a942>] lock_acquire+0x92/0x101
> [ 29.644027] [<8142f11d>] _raw_spin_lock_irqsave+0x2e/0x3e
> [ 29.644027] [<8103c918>] __hrtimer_start_range_ns+0x1c/0x197
> [ 29.644027] [<8107ec20>] perf_swevent_start_hrtimer.part.41+0x7a/0x85
> [ 29.644027] [<81080792>] task_clock_event_start+0x3a/0x3f
> [ 29.644027] [<810807a4>] task_clock_event_add+0xd/0x14
> [ 29.644027] [<8108259a>] event_sched_in+0xb6/0x17a
> [ 29.644027] [<810826a2>] group_sched_in+0x44/0x122
> [ 29.644027] [<81082885>] ctx_sched_in.isra.67+0x105/0x11f
> [ 29.644027] [<810828e6>] perf_event_sched_in.isra.70+0x47/0x4b
> [ 29.644027] [<81082bf6>] __perf_install_in_context+0x8b/0xa3
> [ 29.644027] [<8107eb8e>] remote_function+0x12/0x2a
> [ 29.644027] [<8105f5af>] smp_call_function_single+0x2d/0x53
> [ 29.644027] [<8107e17d>] task_function_call+0x30/0x36
> [ 29.644027] [<8107fb82>] perf_install_in_context+0x87/0xbb
> [ 29.644027] [<810852c9>] SYSC_perf_event_open+0x5c6/0x701
> [ 29.644027] [<810856f9>] SyS_perf_event_open+0x17/0x19
> [ 29.644027] [<8142f8ee>] syscall_call+0x7/0xb
> [ 29.644027]
> [ 29.644027] -> #4 (&ctx->lock){......}:
> [ 29.644027] [<8104a942>] lock_acquire+0x92/0x101
> [ 29.644027] [<8142f04c>] _raw_spin_lock+0x21/0x30
> [ 29.644027] [<81081df3>] __perf_event_task_sched_out+0x1dc/0x34f
> [ 29.644027] [<8142cacc>] __schedule+0x4c6/0x4cb
> [ 29.644027] [<8142cae0>] schedule+0xf/0x11
> [ 29.644027] [<8142f9a6>] work_resched+0x5/0x30
> [ 29.644027]
> [ 29.644027] -> #3 (&rq->lock){-.-.-.}:
> [ 29.644027] [<8104a942>] lock_acquire+0x92/0x101
> [ 29.644027] [<8142f04c>] _raw_spin_lock+0x21/0x30
> [ 29.644027] [<81040873>] __task_rq_lock+0x33/0x3a
> [ 29.644027] [<8104184c>] wake_up_new_task+0x25/0xc2
> [ 29.644027] [<8102474b>] do_fork+0x15c/0x2a0
> [ 29.644027] [<810248a9>] kernel_thread+0x1a/0x1f
> [ 29.644027] [<814232a2>] rest_init+0x1a/0x10e
> [ 29.644027] [<817af949>] start_kernel+0x303/0x308
> [ 29.644027] [<817af2ab>] i386_start_kernel+0x79/0x7d
> [ 29.644027]
> [ 29.644027] -> #2 (&p->pi_lock){-.-...}:
> [ 29.644027] [<8104a942>] lock_acquire+0x92/0x101
> [ 29.644027] [<8142f11d>] _raw_spin_lock_irqsave+0x2e/0x3e
> [ 29.644027] [<810413dd>] try_to_wake_up+0x1d/0xd6
> [ 29.644027] [<810414cd>] default_wake_function+0xb/0xd
> [ 29.644027] [<810461f3>] __wake_up_common+0x39/0x59
> [ 29.644027] [<81046346>] __wake_up+0x29/0x3b
> [ 29.644027] [<811b8733>] tty_wakeup+0x49/0x51
> [ 29.644027] [<811c3568>] uart_write_wakeup+0x17/0x19
> [ 29.644027] [<811c5dc1>] serial8250_tx_chars+0xbc/0xfb
> [ 29.644027] [<811c5f28>] serial8250_handle_irq+0x54/0x6a
> [ 29.644027] [<811c5f57>] serial8250_default_handle_irq+0x19/0x1c
> [ 29.644027] [<811c56d8>] serial8250_interrupt+0x38/0x9e
> [ 29.644027] [<810510e7>] handle_irq_event_percpu+0x5f/0x1e2
> [ 29.644027] [<81051296>] handle_irq_event+0x2c/0x43
> [ 29.644027] [<81052cee>] handle_level_irq+0x57/0x80
> [ 29.644027] [<81002a72>] handle_irq+0x46/0x5c
> [ 29.644027] [<810027df>] do_IRQ+0x32/0x89
> [ 29.644027] [<8143036e>] common_interrupt+0x2e/0x33
> [ 29.644027] [<8142f23c>] _raw_spin_unlock_irqrestore+0x3f/0x49
> [ 29.644027] [<811c25a4>] uart_start+0x2d/0x32
> [ 29.644027] [<811c2c04>] uart_write+0xc7/0xd6
> [ 29.644027] [<811bc6f6>] n_tty_write+0xb8/0x35e
> [ 29.644027] [<811b9beb>] tty_write+0x163/0x1e4
> [ 29.644027] [<811b9cd9>] redirected_tty_write+0x6d/0x75
> [ 29.644027] [<810b6ed6>] vfs_write+0x75/0xb0
> [ 29.644027] [<810b7265>] SyS_write+0x44/0x77
> [ 29.644027] [<8142f8ee>] syscall_call+0x7/0xb
> [ 29.644027]
> [ 29.644027] -> #1 (&tty->write_wait){-.....}:
> [ 29.644027] [<8104a942>] lock_acquire+0x92/0x101
> [ 29.644027] [<8142f11d>] _raw_spin_lock_irqsave+0x2e/0x3e
> [ 29.644027] [<81046332>] __wake_up+0x15/0x3b
> [ 29.644027] [<811b8733>] tty_wakeup+0x49/0x51
> [ 29.644027] [<811c3568>] uart_write_wakeup+0x17/0x19
> [ 29.644027] [<811c5dc1>] serial8250_tx_chars+0xbc/0xfb
> [ 29.644027] [<811c5f28>] serial8250_handle_irq+0x54/0x6a
> [ 29.644027] [<811c5f57>] serial8250_default_handle_irq+0x19/0x1c
> [ 29.644027] [<811c56d8>] serial8250_interrupt+0x38/0x9e
> [ 29.644027] [<810510e7>] handle_irq_event_percpu+0x5f/0x1e2
> [ 29.644027] [<81051296>] handle_irq_event+0x2c/0x43
> [ 29.644027] [<81052cee>] handle_level_irq+0x57/0x80
> [ 29.644027] [<81002a72>] handle_irq+0x46/0x5c
> [ 29.644027] [<810027df>] do_IRQ+0x32/0x89
> [ 29.644027] [<8143036e>] common_interrupt+0x2e/0x33
> [ 29.644027] [<8142f23c>] _raw_spin_unlock_irqrestore+0x3f/0x49
> [ 29.644027] [<811c25a4>] uart_start+0x2d/0x32
> [ 29.644027] [<811c2c04>] uart_write+0xc7/0xd6
> [ 29.644027] [<811bc6f6>] n_tty_write+0xb8/0x35e
> [ 29.644027] [<811b9beb>] tty_write+0x163/0x1e4
> [ 29.644027] [<811b9cd9>] redirected_tty_write+0x6d/0x75
> [ 29.644027] [<810b6ed6>] vfs_write+0x75/0xb0
> [ 29.644027] [<810b7265>] SyS_write+0x44/0x77
> [ 29.644027] [<8142f8ee>] syscall_call+0x7/0xb
> [ 29.644027]
> [ 29.644027] -> #0 (&port_lock_key){-.....}:
> [ 29.644027] [<8104a62d>] __lock_acquire+0x9ea/0xc6d
> [ 29.644027] [<8104a942>] lock_acquire+0x92/0x101
> [ 29.644027] [<8142f11d>] _raw_spin_lock_irqsave+0x2e/0x3e
> [ 29.644027] [<811c60be>] serial8250_console_write+0x8c/0x10c
> [ 29.644027] [<8104e402>] call_console_drivers.constprop.31+0x87/0x118
> [ 29.644027] [<8104f5d5>] console_unlock+0x1d7/0x398
> [ 29.644027] [<8104fb70>] vprintk_emit+0x3da/0x3e4
> [ 29.644027] [<81425f76>] printk+0x17/0x19
> [ 29.644027] [<8105bfa0>] clockevents_program_min_delta+0x104/0x116
> [ 29.644027] [<8105c548>] clockevents_program_event+0xe7/0xf3
> [ 29.644027] [<8105cc1c>] tick_program_event+0x1e/0x23
> [ 29.644027] [<8103c43c>] hrtimer_force_reprogram+0x88/0x8f
> [ 29.644027] [<8103c49e>] __remove_hrtimer+0x5b/0x79
> [ 29.644027] [<8103cb21>] hrtimer_try_to_cancel+0x49/0x66
> [ 29.644027] [<8103cb4b>] hrtimer_cancel+0xd/0x18
> [ 29.644027] [<8107f102>] perf_swevent_cancel_hrtimer.part.60+0x2b/0x30
> [ 29.644027] [<81080705>] task_clock_event_stop+0x20/0x64
> [ 29.644027] [<81080756>] task_clock_event_del+0xd/0xf
> [ 29.644027] [<81081350>] event_sched_out+0xab/0x11e
> [ 29.644027] [<810813e0>] group_sched_out+0x1d/0x66
> [ 29.644027] [<81081682>] ctx_sched_out+0xaf/0xbf
> [ 29.644027] [<81081e04>] __perf_event_task_sched_out+0x1ed/0x34f
> [ 29.644027] [<8142cacc>] __schedule+0x4c6/0x4cb
> [ 29.644027] [<8142cae0>] schedule+0xf/0x11
> [ 29.644027] [<8142f9a6>] work_resched+0x5/0x30
> [ 29.644027]
> [ 29.644027] other info that might help us debug this:
> [ 29.644027]
> [ 29.644027] Chain exists of:
> [ 29.644027] &port_lock_key --> &ctx->lock --> hrtimer_bases.lock
> [ 29.644027]
> [ 29.644027] Possible unsafe locking scenario:
> [ 29.644027]
> [ 29.644027] CPU0 CPU1
> [ 29.644027] ---- ----
> [ 29.644027] lock(hrtimer_bases.lock);
> [ 29.644027] lock(&ctx->lock);
> [ 29.644027] lock(hrtimer_bases.lock);
> [ 29.644027] lock(&port_lock_key);
> [ 29.644027]
> [ 29.644027] *** DEADLOCK ***
> [ 29.644027]
> [ 29.644027] 4 locks held by trinity-main/74:
> [ 29.644027] #0: (&rq->lock){-.-.-.}, at: [<8142c6f3>] __schedule+0xed/0x4cb
> [ 29.644027] #1: (&ctx->lock){......}, at: [<81081df3>] __perf_event_task_sched_out+0x1dc/0x34f
> [ 29.644027] #2: (hrtimer_bases.lock){-.-...}, at: [<8103caeb>] hrtimer_try_to_cancel+0x13/0x66
> [ 29.644027] #3: (console_lock){+.+...}, at: [<8104fb5d>] vprintk_emit+0x3c7/0x3e4
> [ 29.644027]
> [ 29.644027] stack backtrace:
> [ 29.644027] CPU: 0 PID: 74 Comm: trinity-main Not tainted 3.15.0-rc8-06195-g939f04b #2
> [ 29.644027] 00000000 81c3a310 8b995c14 81426f69 8b995c44 81425a99 8161f671 8161f570
> [ 29.644027] 8161f538 8161f559 8161f538 8b995c78 8b142bb0 00000004 8b142fdc 8b142bb0
> [ 29.644027] 8b995ca8 8104a62d 8b142fac 000016f2 81c3a310 00000001 00000001 00000003
> [ 29.644027] Call Trace:
> [ 29.644027] [<81426f69>] dump_stack+0x16/0x18
> [ 29.644027] [<81425a99>] print_circular_bug+0x18f/0x19c
> [ 29.644027] [<8104a62d>] __lock_acquire+0x9ea/0xc6d
> [ 29.644027] [<8104a942>] lock_acquire+0x92/0x101
> [ 29.644027] [<811c60be>] ? serial8250_console_write+0x8c/0x10c
> [ 29.644027] [<811c6032>] ? wait_for_xmitr+0x76/0x76
> [ 29.644027] [<8142f11d>] _raw_spin_lock_irqsave+0x2e/0x3e
> [ 29.644027] [<811c60be>] ? serial8250_console_write+0x8c/0x10c
> [ 29.644027] [<811c60be>] serial8250_console_write+0x8c/0x10c
> [ 29.644027] [<8104af87>] ? lock_release+0x191/0x223
> [ 29.644027] [<811c6032>] ? wait_for_xmitr+0x76/0x76
> [ 29.644027] [<8104e402>] call_console_drivers.constprop.31+0x87/0x118
> [ 29.644027] [<8104f5d5>] console_unlock+0x1d7/0x398
> [ 29.644027] [<8104fb70>] vprintk_emit+0x3da/0x3e4
> [ 29.644027] [<81425f76>] printk+0x17/0x19
> [ 29.644027] [<8105bfa0>] clockevents_program_min_delta+0x104/0x116
> [ 29.644027] [<8105c548>] clockevents_program_event+0xe7/0xf3
> [ 29.644027] [<8105cc1c>] tick_program_event+0x1e/0x23
> [ 29.644027] [<8103c43c>] hrtimer_force_reprogram+0x88/0x8f
> [ 29.644027] [<8103c49e>] __remove_hrtimer+0x5b/0x79
> [ 29.644027] [<8103cb21>] hrtimer_try_to_cancel+0x49/0x66
> [ 29.644027] [<8103cb4b>] hrtimer_cancel+0xd/0x18
> [ 29.644027] [<8107f102>] perf_swevent_cancel_hrtimer.part.60+0x2b/0x30
> [ 29.644027] [<81080705>] task_clock_event_stop+0x20/0x64
> [ 29.644027] [<81080756>] task_clock_event_del+0xd/0xf
> [ 29.644027] [<81081350>] event_sched_out+0xab/0x11e
> [ 29.644027] [<810813e0>] group_sched_out+0x1d/0x66
> [ 29.644027] [<81081682>] ctx_sched_out+0xaf/0xbf
> [ 29.644027] [<81081e04>] __perf_event_task_sched_out+0x1ed/0x34f
> [ 29.644027] [<8104416d>] ? __dequeue_entity+0x23/0x27
> [ 29.644027] [<81044505>] ? pick_next_task_fair+0xb1/0x120
> [ 29.644027] [<8142cacc>] __schedule+0x4c6/0x4cb
> [ 29.644027] [<81047574>] ? trace_hardirqs_off_caller+0xd7/0x108
> [ 29.644027] [<810475b0>] ? trace_hardirqs_off+0xb/0xd
> [ 29.644027] [<81056346>] ? rcu_irq_exit+0x64/0x77
>
> git bisect start 9f6226a762c7ae02f6a23a3d4fc552dafa57ea23 v3.15 --
> git bisect bad 71998d1be4ae70e7d320cdd21595c1a02a29c61e # 01:13 79- 5 Merge branch 'x86-irq-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> git bisect bad 9ee4d7a6538308a7681b638d2f35f2a301420355 # 01:24 3- 1 Merge branch 'akpm' (patches from Andrew Morton)
> git bisect bad 9894e6d9c020b754dd962960e9f7eac18282f69f # 01:58 128- 5 Merge tag 'fbdev-omap-dt-3.16' of git://git.kernel.org/pub/scm/linux/kernel/git/tomba/linux
> git bisect bad 963649d735c8b6eb0f97e82c54f02426ff3f1f45 # 02:06 48- 3 Merge tag 'for-linus-3.16-merge-window' of git://git.kernel.org/pub/scm/linux/kernel/git/ericvh/v9fs
> git bisect bad b20dcab9d4589ef9918a13c888c5493945adfc13 # 02:13 35- 1 Merge tag 'llvmlinux-for-v3.16' of git://git.linuxfoundation.org/llvmlinux/kernel
> git bisect bad 3f17ea6dea8ba5668873afa54628a91aaa3fb1c0 # 02:19 58- 4 Merge branch 'next' (accumulated 3.16 merge window patches) into master
> git bisect good 49eb7b0750d9483c74e9c14ae6ea1e9d62481c3c # 02:35 300+ 7 Merge tag 'tty-3.16-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty into next
> git bisect good 15b588303155b22edd559672905db8e59a44ef9a # 02:51 300+ 0 Merge tag 'fbdev-omap-3.16' of git://git.kernel.org/pub/scm/linux/kernel/git/tomba/linux into next
> git bisect good d09cc3659db494aca4b3bb2393c533fb4946b794 # 03:19 300+ 1 Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next
> git bisect bad cc07aabc53978ae09a1d539237189f7c9841060a # 03:37 66- 2 Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux into next
> git bisect bad 8091b895b76f690aa2f6689b6ed602f07525a938 # 04:55 103- 1 fs/ncpfs/getopt.c: replace simple_strtoul by kstrtoul
> git bisect good d53aea3d46d64e95da9952887969f7533b9ab25e # 05:59 300+ 19 mm, compaction: return failed migration target pages back to freelist
> git bisect good 72d09633c9afa02bea317d65eb8b8a4ce7659a2a # 06:31 300+ 10 mm/zswap: NUMA aware allocation for zswap_dstmem
> git bisect bad 0046dd9fed0c9313cbb4fb860324476cd298dc9f # 06:35 42- 1 lib/string.c: use the name "C-string" in comments
> git bisect good 0a581694ab7a5bc083d710df8a552a6a055b005f # 06:54 300+ 15 printk: split code for making free space in the log buffer
> git bisect bad 939f04bec1a4ef6ba4370b0f34b01decc844b1b1 # 06:58 46- 2 printk: enable interrupts before calling console_trylock_for_printk()
> git bisect good 034633ccb24d675850f99bf85c1c5880c831e4b6 # 07:16 300+ 28 printk: return really stored message length
> git bisect good 608873cacb9d0d2811586fcc79a38b64eabd6d32 # 07:29 300+ 22 printk: release lockbuf_lock before calling console_trylock_for_printk()
> git bisect good bd8d7cf5b8410fe98eba06a9aaa90efe88815d8a # 07:42 300+ 7 printk: fix lockdep instrumentation of console_sem
> # first bad commit: [939f04bec1a4ef6ba4370b0f34b01decc844b1b1] printk: enable interrupts before calling console_trylock_for_printk()
> git bisect good bd8d7cf5b8410fe98eba06a9aaa90efe88815d8a # 08:21 900+ 41 printk: fix lockdep instrumentation of console_sem
> git bisect bad fb3ec67942e92e5713e05b7691b277d0a0c0575d # 08:21 0- 5 KVM: arm64: GICv3: mandate page-aligned GICV region
> git bisect good 6f0928036bcbd8dd2ebee9201580da8bcc0a81af # 08:49 900+ 87 Merge tag 'pm+acpi-3.16-rc8' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm
>
>
> This script may reproduce the error.
>
> ----------------------------------------------------------------------------
> #!/bin/bash
>
> kernel=$1
> initrd=quantal-core-i386.cgz
>
> wget --no-clobber https://github.com/fengguang/reproduce-kernel-bug/raw/master/initrd/$initrd
>
> kvm=(
> qemu-system-x86_64
> -enable-kvm
> -cpu Haswell,+smep,+smap
> -kernel $kernel
> -initrd $initrd
> -m 320
> -smp 2
> -net nic,vlan=1,model=e1000
> -net user,vlan=1
> -boot order=nc
> -no-reboot
> -watchdog i6300esb
> -rtc base=localtime
> -serial stdio
> -display none
> -monitor null
> )
>
> append=(
> hung_task_panic=1
> earlyprintk=ttyS0,115200
> debug
> apic=debug
> sysrq_always_enabled
> rcupdate.rcu_cpu_stall_timeout=100
> panic=10
> softlockup_panic=1
> nmi_watchdog=panic
> prompt_ramdisk=0
> console=ttyS0,115200
> console=tty0
> vga=normal
> root=/dev/ram0
> rw
> drbd.minor_count=8
> )
>
> "${kvm[@]}" --append "${append[*]}"
> ----------------------------------------------------------------------------

--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR

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