"Fix data race in tty_insert_flip_string_fixed_flag" triggers a lockdep warning

[Qian Cai]

The commit b6da31b2c07c ("tty: Fix data race in
tty_insert_flip_string_fixed_flag") creates a locking order,

&(&port->lock)->rlock --> &(&zone->lock)->rlock

which will trigger a lockdep warning below.

[ÂÂ489.312784] WARNING: possible circular locking dependency detected
[ÂÂ489.319655] 5.4.0-rc5-next-20191030+ #2 Tainted: GÂÂÂÂÂÂÂÂWÂÂÂÂLÂÂÂ
[ÂÂ489.326610] ------------------------------------------------------
[ÂÂ489.333479] sshd/5541 is trying to acquire lock:
[ÂÂ489.338785] ffff008b7cff9290 (&(&zone->lock)->rlock){..-.}, at:
rmqueue+0xfe8/0x2274
[ÂÂ489.347230]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂbut task is already holding lock:
[ÂÂ489.354444] 1cff0009e39c0540 (&(&port->lock)->rlock){-.-.}, at:
pty_write+0x60/0xd0
[ÂÂ489.362799]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂwhich lock already depends on the new lock.

[ÂÂ489.373052]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂthe existing dependency chain (in reverse order) is:
[ÂÂ489.381916]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ-> #3 (&(&port->lock)->rlock){-.-.}:
[ÂÂ489.389403]ÂÂÂÂÂÂÂÂlock_acquire+0x320/0x360
[ÂÂ489.394279]ÂÂÂÂÂÂÂÂ_raw_spin_lock_irqsave+0x7c/0x9c
[ÂÂ489.399849]ÂÂÂÂÂÂÂÂtty_port_tty_get+0x24/0x60
[ÂÂ489.404896]ÂÂÂÂÂÂÂÂtty_port_default_wakeup+0x1c/0x3c
[ÂÂ489.410551]ÂÂÂÂÂÂÂÂtty_port_tty_wakeup+0x34/0x40
[ÂÂ489.415859]ÂÂÂÂÂÂÂÂuart_write_wakeup+0x28/0x44
[ÂÂ489.420993]ÂÂÂÂÂÂÂÂpl011_tx_chars+0x1b8/0x270
[ÂÂ489.426040]ÂÂÂÂÂÂÂÂpl011_start_tx+0x24/0x70
[ÂÂ489.430913]ÂÂÂÂÂÂÂÂ__uart_start+0x5c/0x68
[ÂÂ489.435612]ÂÂÂÂÂÂÂÂuart_write+0x164/0x1c8
[ÂÂ489.440312]ÂÂÂÂÂÂÂÂdo_output_char+0x33c/0x348
[ÂÂ489.445358]ÂÂÂÂÂÂÂÂn_tty_write+0x4bc/0x60c
[ÂÂ489.450143]ÂÂÂÂÂÂÂÂtty_write+0x338/0x474
[ÂÂ489.454755]ÂÂÂÂÂÂÂÂredirected_tty_write+0xc0/0xdc
[ÂÂ489.460150]ÂÂÂÂÂÂÂÂdo_loop_readv_writev+0x140/0x180
[ÂÂ489.465718]ÂÂÂÂÂÂÂÂdo_iter_write+0xe0/0x10c
[ÂÂ489.470590]ÂÂÂÂÂÂÂÂvfs_writev+0x134/0x1cc
[ÂÂ489.475289]ÂÂÂÂÂÂÂÂdo_writev+0xbc/0x130
[ÂÂ489.479815]ÂÂÂÂÂÂÂÂ__arm64_sys_writev+0x58/0x8c
[ÂÂ489.485038]ÂÂÂÂÂÂÂÂel0_svc_handler+0x170/0x240
[ÂÂ489.490173]ÂÂÂÂÂÂÂÂel0_sync_handler+0x150/0x250
[ÂÂ489.495393]ÂÂÂÂÂÂÂÂel0_sync+0x164/0x180
[ÂÂ489.499915]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ-> #2 (&port_lock_key){-.-.}:
[ÂÂ489.506793]ÂÂÂÂÂÂÂÂlock_acquire+0x320/0x360
[ÂÂ489.511666]ÂÂÂÂÂÂÂÂ_raw_spin_lock+0x64/0x80
[ÂÂ489.516540]ÂÂÂÂÂÂÂÂpl011_console_write+0xec/0x2cc
[ÂÂ489.521934]ÂÂÂÂÂÂÂÂconsole_unlock+0x794/0x96c
[ÂÂ489.526981]ÂÂÂÂÂÂÂÂvprintk_emit+0x260/0x31c
[ÂÂ489.531854]ÂÂÂÂÂÂÂÂvprintk_default+0x54/0x7c
[ÂÂ489.536813]ÂÂÂÂÂÂÂÂvprintk_func+0x218/0x254
[ÂÂ489.541687]ÂÂÂÂÂÂÂÂprintk+0x7c/0xa4

ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ-> #1 (console_owner){-...}:
[ÂÂ489.703613]ÂÂÂÂÂÂÂÂlock_acquire+0x320/0x360
[ÂÂ489.708486]ÂÂÂÂÂÂÂÂconsole_lock_spinning_enable+0x6c/0x7c
[ÂÂ489.714575]ÂÂÂÂÂÂÂÂconsole_unlock+0x4f8/0x96c
[ÂÂ489.719622]ÂÂÂÂÂÂÂÂvprintk_emit+0x260/0x31c
[ÂÂ489.724495]ÂÂÂÂÂÂÂÂvprintk_default+0x54/0x7c
[ÂÂ489.729454]ÂÂÂÂÂÂÂÂvprintk_func+0x218/0x254
[ÂÂ489.734327]ÂÂÂÂÂÂÂÂprintk+0x7c/0xa4
[ÂÂ489.810371]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ-> #0 (&(&zone->lock)->rlock){..-.}:
[ÂÂ489.817854]ÂÂÂÂÂÂÂÂvalidate_chain+0xf6c/0x2e2c
[ÂÂ489.822988]ÂÂÂÂÂÂÂÂ__lock_acquire+0x868/0xc2c
[ÂÂ489.828035]ÂÂÂÂÂÂÂÂlock_acquire+0x320/0x360
[ÂÂ489.832909]ÂÂÂÂÂÂÂÂ_raw_spin_lock_irqsave+0x7c/0x9c
[ÂÂ489.838475]ÂÂÂÂÂÂÂÂrmqueue+0xfe8/0x2274
[ÂÂ489.843002]ÂÂÂÂÂÂÂÂget_page_from_freelist+0x474/0x688
[ÂÂ489.848743]ÂÂÂÂÂÂÂÂ__alloc_pages_nodemask+0x3b8/0x1928
[ÂÂ489.854573]ÂÂÂÂÂÂÂÂalloc_pages_current+0xd0/0xe0
[ÂÂ489.859882]ÂÂÂÂÂÂÂÂstack_depot_save+0x300/0x440
[ÂÂ489.865103]ÂÂÂÂÂÂÂÂ__kasan_kmalloc+0x198/0x1e0
[ÂÂ489.870236]ÂÂÂÂÂÂÂÂkasan_slab_alloc+0x18/0x20
[ÂÂ489.875284]ÂÂÂÂÂÂÂÂslab_post_alloc_hook+0x48/0x9c
[ÂÂ489.880677]ÂÂÂÂÂÂÂÂkmem_cache_alloc+0x2e8/0x588
[ÂÂ489.885898]ÂÂÂÂÂÂÂÂcreate_object+0x60/0x698
[ÂÂ489.890771]ÂÂÂÂÂÂÂÂkmemleak_alloc+0x78/0xb8
[ÂÂ489.895644]ÂÂÂÂÂÂÂÂslab_post_alloc_hook+0x64/0x9c
[ÂÂ489.901038]ÂÂÂÂÂÂÂÂ__kmalloc+0x328/0x490
[ÂÂ489.905652]ÂÂÂÂÂÂÂÂ__tty_buffer_request_room+0x118/0x1f8
[ÂÂ489.911654]ÂÂÂÂÂÂÂÂtty_insert_flip_string_fixed_flag+0x6c/0x144
[ÂÂ489.918263]ÂÂÂÂÂÂÂÂpty_write+0x80/0xd0
[ÂÂ489.922701]ÂÂÂÂÂÂÂÂn_tty_write+0x450/0x60c
[ÂÂ489.927486]ÂÂÂÂÂÂÂÂtty_write+0x338/0x474
[ÂÂ489.932098]ÂÂÂÂÂÂÂÂ__vfs_write+0x88/0x214
[ÂÂ489.936796]ÂÂÂÂÂÂÂÂvfs_write+0x12c/0x1a4
[ÂÂ489.941411]ÂÂÂÂÂÂÂÂksys_write+0xb0/0x120
[ÂÂ489.946027]ÂÂÂÂÂÂÂÂ__arm64_sys_write+0x54/0x88
[ÂÂ489.951161]ÂÂÂÂÂÂÂÂel0_svc_handler+0x170/0x240
[ÂÂ489.956294]ÂÂÂÂÂÂÂÂel0_sync_handler+0x150/0x250
[ÂÂ489.961514]ÂÂÂÂÂÂÂÂel0_sync+0x164/0x180
[ÂÂ489.966038]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂother info that might help us debug this:

[ÂÂ489.976117] Chain exists of:
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ&(&zone->lock)->rlock --> &port_lock_key --> &(&port->lock)-
>rlock

[ÂÂ489.989937]ÂÂPossible unsafe locking scenario:

[ÂÂ489.997239]ÂÂÂÂÂÂÂÂCPU0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂCPU1
[ÂÂ490.002456]ÂÂÂÂÂÂÂÂ----ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ----
[ÂÂ490.007673]ÂÂÂlock(&(&port->lock)->rlock);
[ÂÂ490.012459]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂlock(&port_lock_key);
[ÂÂ490.019155]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂlock(&(&port->lock)->rlock);
[ÂÂ490.026458]ÂÂÂlock(&(&zone->lock)->rlock);
[ÂÂ490.031244]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ*** DEADLOCK ***

[ÂÂ490.039241] 5 locks held by sshd/5541:
[ÂÂ490.043677]ÂÂ#0: 12ff0009eb0c6890 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x3c/0x48
[ÂÂ490.052465]ÂÂ#1: 12ff0009eb0c6918 (&tty->atomic_write_lock){+.+.}, at:
tty_write+0x12c/0x474
[ÂÂ490.061599]ÂÂ#2: 12ff0009eb0c6aa0 (&o_tty->termios_rwsem/1){++++}, at:
n_tty_write+0x10c/0x60c
[ÂÂ490.070908]ÂÂ#3: ffff90001f852360 (&ldata->output_lock){+.+.}, at:
n_tty_write+0x278/0x60c
[ÂÂ490.079868]ÂÂ#4: 1cff0009e39c0540 (&(&port->lock)->rlock){-.-.}, at:
pty_write+0x60/0xd0
[ÂÂ490.088654]Â
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂstack backtrace:
[ÂÂ490.094398] CPU: 31 PID: 5541 Comm: sshd Tainted: GÂÂÂÂÂÂÂÂWÂÂÂÂLÂÂÂÂ5.4.0-
rc5-next-20191030+ #2
[ÂÂ490.103871] Hardware name: HPE Apollo 70ÂÂÂÂÂÂÂÂÂÂÂÂÂ/C01_APACHE_MBÂÂÂÂÂÂÂÂÂ,
BIOS L50_5.13_1.11 06/18/2019
[ÂÂ490.114300] Call trace:
[ÂÂ490.117438]ÂÂdump_backtrace+0x0/0x248
[ÂÂ490.121791]ÂÂshow_stack+0x20/0x2c
[ÂÂ490.125798]ÂÂdump_stack+0xc8/0x130
[ÂÂ490.129890]ÂÂprint_circular_bug+0x368/0x380
[ÂÂ490.134764]ÂÂcheck_noncircular+0x28c/0x294
[ÂÂ490.139550]ÂÂvalidate_chain+0xf6c/0x2e2c
[ÂÂ490.144164]ÂÂ__lock_acquire+0x868/0xc2c
[ÂÂ490.148691]ÂÂlock_acquire+0x320/0x360
[ÂÂ490.153044]ÂÂ_raw_spin_lock_irqsave+0x7c/0x9c
[ÂÂ490.158090]ÂÂrmqueue+0xfe8/0x2274
[ÂÂ490.162097]ÂÂget_page_from_freelist+0x474/0x688
[ÂÂ490.167317]ÂÂ__alloc_pages_nodemask+0x3b8/0x1928
[ÂÂ490.172625]ÂÂalloc_pages_current+0xd0/0xe0
[ÂÂ490.177412]ÂÂstack_depot_save+0x300/0x440
[ÂÂ490.182112]ÂÂ__kasan_kmalloc+0x198/0x1e0
[ÂÂ490.186723]ÂÂkasan_slab_alloc+0x18/0x20
[ÂÂ490.191249]ÂÂslab_post_alloc_hook+0x48/0x9c
[ÂÂ490.196121]ÂÂkmem_cache_alloc+0x2e8/0x588
[ÂÂ490.200820]ÂÂcreate_object+0x60/0x698
[ÂÂ490.205173]ÂÂkmemleak_alloc+0x78/0xb8
[ÂÂ490.209525]ÂÂslab_post_alloc_hook+0x64/0x9c
[ÂÂ490.214398]ÂÂ__kmalloc+0x328/0x490
[ÂÂ490.218491]ÂÂ__tty_buffer_request_room+0x118/0x1f8
[ÂÂ490.223972]ÂÂtty_insert_flip_string_fixed_flag+0x6c/0x144
[ÂÂ490.230059]ÂÂpty_write+0x80/0xd0
[ÂÂ490.233977]ÂÂn_tty_write+0x450/0x60c
[ÂÂ490.238241]ÂÂtty_write+0x338/0x474
[ÂÂ490.242333]ÂÂ__vfs_write+0x88/0x214
[ÂÂ490.246511]ÂÂvfs_write+0x12c/0x1a4
[ÂÂ490.250601]ÂÂksys_write+0xb0/0x120
[ÂÂ490.254693]ÂÂ__arm64_sys_write+0x54/0x88
[ÂÂ490.259305]ÂÂel0_svc_handler+0x170/0x240
[ÂÂ490.263918]ÂÂel0_sync_handler+0x150/0x250
[ÂÂ490.268617]ÂÂel0_sync+0x164/0x180