Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

Qian Cai
2019-10-09T14:19:51Z

On Wed, 2019-10-09 at 15:51 +0200, Michal Hocko wrote:
> On Wed 09-10-19 09:43:13, Qian Cai wrote:
> > On Wed, 2019-10-09 at 15:27 +0200, Michal Hocko wrote:
> > > On Wed 09-10-19 09:06:42, Qian Cai wrote:
> > > [...]
> > > > https://lore.kernel.org/linux-mm/1570460350.5576.290.camel@lca.pw/
> > > >
> > > > [  297.425964] -> #1 (&port_lock_key){-.-.}:
> > > > [  297.425967]        __lock_acquire+0x5b3/0xb40
> > > > [  297.425967]        lock_acquire+0x126/0x280
> > > > [  297.425968]        _raw_spin_lock_irqsave+0x3a/0x50
> > > > [  297.425969]        serial8250_console_write+0x3e4/0x450
> > > > [  297.425970]        univ8250_console_write+0x4b/0x60
> > > > [  297.425970]        console_unlock+0x501/0x750
> > > > [  297.425971]        vprintk_emit+0x10d/0x340
> > > > [  297.425972]        vprintk_default+0x1f/0x30
> > > > [  297.425972]        vprintk_func+0x44/0xd4
> > > > [  297.425973]        printk+0x9f/0xc5
> > > > [  297.425974]        register_console+0x39c/0x520
> > > > [  297.425975]        univ8250_console_init+0x23/0x2d
> > > > [  297.425975]        console_init+0x338/0x4cd
> > > > [  297.425976]        start_kernel+0x534/0x724
> > > > [  297.425977]        x86_64_start_reservations+0x24/0x26
> > > > [  297.425977]        x86_64_start_kernel+0xf4/0xfb
> > > > [  297.425978]        secondary_startup_64+0xb6/0xc0
> > > >
> > > > where the report again show the early boot call trace for the locking
> > > > dependency,
> > > >
> > > > console_owner --> port_lock_key
> > > >
> > > > but that dependency clearly not only happen in the early boot.
> > >
> > > Can you provide an example of the runtime dependency without any early
> > > boot artifacts? Because this discussion really doens't make much sense
> > > without a clear example of a _real_ lockdep report that is not a false
> > > possitive. All of them so far have been concluded to be false possitive
> > > AFAIU.
> >
> > An obvious one is in the above link. Just replace the trace in #1 above with
> > printk() from anywhere, i.e., just ignore the early boot calls there as they are
> > not important.
> >
> > printk()
> > console_unlock()
> > console_lock_spinning_enable() --> console_owner_lock
> > call_console_drivers()
> > serial8250_console_write() --> port->lock
>
> Can you paste the full lock chain graph to be sure we are on the same
> page?

WARNING: possible circular locking dependency detected
5.3.0-next-20190917 #8 Not tainted
------------------------------------------------------
test.sh/8653 is trying to acquire lock:
ffffffff865a4460 (console_owner){-.-.}, at:
console_unlock+0x207/0x750

but task is already holding lock:
ffff88883fff3c58 (&(&zone->lock)->rlock){-.-.}, at:
__offline_isolated_pages+0x179/0x3e0

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (&(&zone->lock)->rlock){-.-.}:
__lock_acquire+0x5b3/0xb40
lock_acquire+0x126/0x280
_raw_spin_lock+0x2f/0x40
rmqueue_bulk.constprop.21+0xb6/0x1160
get_page_from_freelist+0x898/0x22c0
__alloc_pages_nodemask+0x2f3/0x1cd0
alloc_pages_current+0x9c/0x110
allocate_slab+0x4c6/0x19c0
new_slab+0x46/0x70
___slab_alloc+0x58b/0x960
__slab_alloc+0x43/0x70
__kmalloc+0x3ad/0x4b0
__tty_buffer_request_room+0x100/0x250
tty_insert_flip_string_fixed_flag+0x67/0x110
pty_write+0xa2/0xf0
n_tty_write+0x36b/0x7b0
tty_write+0x284/0x4c0
__vfs_write+0x50/0xa0
vfs_write+0x105/0x290
redirected_tty_write+0x6a/0xc0
do_iter_write+0x248/0x2a0
vfs_writev+0x106/0x1e0
do_writev+0xd4/0x180
__x64_sys_writev+0x45/0x50
do_syscall_64+0xcc/0x76c
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (&(&port->lock)->rlock){-.-.}:
__lock_acquire+0x5b3/0xb40
lock_acquire+0x126/0x280
_raw_spin_lock_irqsave+0x3a/0x50
tty_port_tty_get+0x20/0x60
tty_port_default_wakeup+0xf/0x30
tty_port_tty_wakeup+0x39/0x40
uart_write_wakeup+0x2a/0x40
serial8250_tx_chars+0x22e/0x440
serial8250_handle_irq.part.8+0x14a/0x170
serial8250_default_handle_irq+0x5c/0x90
serial8250_interrupt+0xa6/0x130
__handle_irq_event_percpu+0x78/0x4f0
handle_irq_event_percpu+0x70/0x100
handle_irq_event+0x5a/0x8b
handle_edge_irq+0x117/0x370
do_IRQ+0x9e/0x1e0
ret_from_intr+0x0/0x2a
cpuidle_enter_state+0x156/0x8e0
cpuidle_enter+0x41/0x70
call_cpuidle+0x5e/0x90
do_idle+0x333/0x370
cpu_startup_entry+0x1d/0x1f
start_secondary+0x290/0x330
secondary_startup_64+0xb6/0xc0

-> #1 (&port_lock_key){-.-.}:
__lock_acquire+0x5b3/0xb40
lock_acquire+0x126/0x280
_raw_spin_lock_irqsave+0x3a/0x50
serial8250_console_write+0x3e4/0x450
univ8250_console_write+0x4b/0x60
console_unlock+0x501/0x750
vprintk_emit+0x10d/0x340
vprintk_default+0x1f/0x30
vprintk_func+0x44/0xd4
printk+0x9f/0xc5

-> #0 (console_owner){-.-.}:
check_prev_add+0x107/0xea0
validate_chain+0x8fc/0x1200
__lock_acquire+0x5b3/0xb40
lock_acquire+0x126/0x280
console_unlock+0x269/0x750
vprintk_emit+0x10d/0x340
vprintk_default+0x1f/0x30
vprintk_func+0x44/0xd4
printk+0x9f/0xc5
__offline_isolated_pages.cold.52+0x2f/0x30a
offline_isolated_pages_cb+0x17/0x30
walk_system_ram_range+0xda/0x160
__offline_pages+0x79c/0xa10
offline_pages+0x11/0x20
memory_subsys_offline+0x7e/0xc0
device_offline+0xd5/0x110
state_store+0xc6/0xe0
dev_attr_store+0x3f/0x60
sysfs_kf_write+0x89/0xb0
kernfs_fop_write+0x188/0x240
__vfs_write+0x50/0xa0
vfs_write+0x105/0x290
ksys_write+0xc6/0x160
__x64_sys_write+0x43/0x50
do_syscall_64+0xcc/0x76c
entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
console_owner --> &(&port->lock)->rlock --> &(&zone->lock)-
>rlock

Possible unsafe locking scenario:

CPU0                    CPU1
----                    ----
lock(&(&zone->lock)->rlock);
lock(&(&port->lock)->rlock);
lock(&(&zone->lock)->rlock);
lock(console_owner);

*** DEADLOCK ***

9 locks held by test.sh/8653:
#0: ffff88839ba7d408 (sb_writers#4){.+.+}, at:
vfs_write+0x25f/0x290
#1: ffff888277618880 (&of->mutex){+.+.}, at:
kernfs_fop_write+0x128/0x240
#2: ffff8898131fc218 (kn->count#115){.+.+}, at:
kernfs_fop_write+0x138/0x240
#3: ffffffff86962a80 (device_hotplug_lock){+.+.}, at:
lock_device_hotplug_sysfs+0x16/0x50
#4: ffff8884374f4990 (&dev->mutex){....}, at:
device_offline+0x70/0x110
#5: ffffffff86515250 (cpu_hotplug_lock.rw_sem){++++}, at:
__offline_pages+0xbf/0xa10
#6: ffffffff867405f0 (mem_hotplug_lock.rw_sem){++++}, at:
percpu_down_write+0x87/0x2f0
#7: ffff88883fff3c58 (&(&zone->lock)->rlock){-.-.}, at:
__offline_isolated_pages+0x179/0x3e0
#8: ffffffff865a4920 (console_lock){+.+.}, at:
vprintk_emit+0x100/0x340

stack backtrace:
CPU: 1 PID: 8653 Comm: test.sh Not tainted 5.3.0-next-20190917 #8
Hardware name: HPE ProLiant DL560 Gen10/ProLiant DL560 Gen10,
BIOS U34 05/21/2019
Call Trace:
dump_stack+0x86/0xca
print_circular_bug.cold.31+0x243/0x26e
check_noncircular+0x29e/0x2e0
check_prev_add+0x107/0xea0
validate_chain+0x8fc/0x1200
__lock_acquire+0x5b3/0xb40
lock_acquire+0x126/0x280
console_unlock+0x269/0x750
vprintk_emit+0x10d/0x340
vprintk_default+0x1f/0x30
vprintk_func+0x44/0xd4
printk+0x9f/0xc5
__offline_isolated_pages.cold.52+0x2f/0x30a
offline_isolated_pages_cb+0x17/0x30
walk_system_ram_range+0xda/0x160
__offline_pages+0x79c/0xa10
offline_pages+0x11/0x20
memory_subsys_offline+0x7e/0xc0
device_offline+0xd5/0x110
state_store+0xc6/0xe0
dev_attr_store+0x3f/0x60
sysfs_kf_write+0x89/0xb0
kernfs_fop_write+0x188/0x240
__vfs_write+0x50/0xa0
vfs_write+0x105/0x290
ksys_write+0xc6/0x160
__x64_sys_write+0x43/0x50
do_syscall_64+0xcc/0x76c
entry_SYSCALL_64_after_hwframe+0x49/0xbe