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Subject[PATCH AUTOSEL 5.5 054/542] char/random: silence a lockdep splat with printk()
Date
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>

[ Upstream commit 1b710b1b10eff9d46666064ea25f079f70bc67a8 ]

Sergey didn't like the locking order,

uart_port->lock -> tty_port->lock

uart_write (uart_port->lock)
__uart_start
pl011_start_tx
pl011_tx_chars
uart_write_wakeup
tty_port_tty_wakeup
tty_port_default
tty_port_tty_get (tty_port->lock)

but those code is so old, and I have no clue how to de-couple it after
checking other locks in the splat. There is an onging effort to make all
printk() as deferred, so until that happens, workaround it for now as a
short-term fix.

LTP: starting iogen01 (export LTPROOT; rwtest -N iogen01 -i 120s -s
read,write -Da -Dv -n 2 500b:$TMPDIR/doio.f1.$$
1000b:$TMPDIR/doio.f2.$$)
WARNING: possible circular locking dependency detected
------------------------------------------------------
doio/49441 is trying to acquire lock:
ffff008b7cff7290 (&(&zone->lock)->rlock){..-.}, at: rmqueue+0x138/0x2050

but task is already holding lock:
60ff000822352818 (&pool->lock/1){-.-.}, at: start_flush_work+0xd8/0x3f0

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #4 (&pool->lock/1){-.-.}:
lock_acquire+0x320/0x360
_raw_spin_lock+0x64/0x80
__queue_work+0x4b4/0xa10
queue_work_on+0xac/0x11c
tty_schedule_flip+0x84/0xbc
tty_flip_buffer_push+0x1c/0x28
pty_write+0x98/0xd0
n_tty_write+0x450/0x60c
tty_write+0x338/0x474
__vfs_write+0x88/0x214
vfs_write+0x12c/0x1a4
redirected_tty_write+0x90/0xdc
do_loop_readv_writev+0x140/0x180
do_iter_write+0xe0/0x10c
vfs_writev+0x134/0x1cc
do_writev+0xbc/0x130
__arm64_sys_writev+0x58/0x8c
el0_svc_handler+0x170/0x240
el0_sync_handler+0x150/0x250
el0_sync+0x164/0x180

-> #3 (&(&port->lock)->rlock){-.-.}:
lock_acquire+0x320/0x360
_raw_spin_lock_irqsave+0x7c/0x9c
tty_port_tty_get+0x24/0x60
tty_port_default_wakeup+0x1c/0x3c
tty_port_tty_wakeup+0x34/0x40
uart_write_wakeup+0x28/0x44
pl011_tx_chars+0x1b8/0x270
pl011_start_tx+0x24/0x70
__uart_start+0x5c/0x68
uart_write+0x164/0x1c8
do_output_char+0x33c/0x348
n_tty_write+0x4bc/0x60c
tty_write+0x338/0x474
redirected_tty_write+0xc0/0xdc
do_loop_readv_writev+0x140/0x180
do_iter_write+0xe0/0x10c
vfs_writev+0x134/0x1cc
do_writev+0xbc/0x130
__arm64_sys_writev+0x58/0x8c
el0_svc_handler+0x170/0x240
el0_sync_handler+0x150/0x250
el0_sync+0x164/0x180

-> #2 (&port_lock_key){-.-.}:
lock_acquire+0x320/0x360
_raw_spin_lock+0x64/0x80
pl011_console_write+0xec/0x2cc
console_unlock+0x794/0x96c
vprintk_emit+0x260/0x31c
vprintk_default+0x54/0x7c
vprintk_func+0x218/0x254
printk+0x7c/0xa4
register_console+0x734/0x7b0
uart_add_one_port+0x734/0x834
pl011_register_port+0x6c/0xac
sbsa_uart_probe+0x234/0x2ec
platform_drv_probe+0xd4/0x124
really_probe+0x250/0x71c
driver_probe_device+0xb4/0x200
__device_attach_driver+0xd8/0x188
bus_for_each_drv+0xbc/0x110
__device_attach+0x120/0x220
device_initial_probe+0x20/0x2c
bus_probe_device+0x54/0x100
device_add+0xae8/0xc2c
platform_device_add+0x278/0x3b8
platform_device_register_full+0x238/0x2ac
acpi_create_platform_device+0x2dc/0x3a8
acpi_bus_attach+0x390/0x3cc
acpi_bus_attach+0x108/0x3cc
acpi_bus_attach+0x108/0x3cc
acpi_bus_attach+0x108/0x3cc
acpi_bus_scan+0x7c/0xb0
acpi_scan_init+0xe4/0x304
acpi_init+0x100/0x114
do_one_initcall+0x348/0x6a0
do_initcall_level+0x190/0x1fc
do_basic_setup+0x34/0x4c
kernel_init_freeable+0x19c/0x260
kernel_init+0x18/0x338
ret_from_fork+0x10/0x18

-> #1 (console_owner){-...}:
lock_acquire+0x320/0x360
console_lock_spinning_enable+0x6c/0x7c
console_unlock+0x4f8/0x96c
vprintk_emit+0x260/0x31c
vprintk_default+0x54/0x7c
vprintk_func+0x218/0x254
printk+0x7c/0xa4
get_random_u64+0x1c4/0x1dc
shuffle_pick_tail+0x40/0xac
__free_one_page+0x424/0x710
free_one_page+0x70/0x120
__free_pages_ok+0x61c/0xa94
__free_pages_core+0x1bc/0x294
memblock_free_pages+0x38/0x48
__free_pages_memory+0xcc/0xfc
__free_memory_core+0x70/0x78
free_low_memory_core_early+0x148/0x18c
memblock_free_all+0x18/0x54
mem_init+0xb4/0x17c
mm_init+0x14/0x38
start_kernel+0x19c/0x530

-> #0 (&(&zone->lock)->rlock){..-.}:
validate_chain+0xf6c/0x2e2c
__lock_acquire+0x868/0xc2c
lock_acquire+0x320/0x360
_raw_spin_lock+0x64/0x80
rmqueue+0x138/0x2050
get_page_from_freelist+0x474/0x688
__alloc_pages_nodemask+0x3b4/0x18dc
alloc_pages_current+0xd0/0xe0
alloc_slab_page+0x2b4/0x5e0
new_slab+0xc8/0x6bc
___slab_alloc+0x3b8/0x640
kmem_cache_alloc+0x4b4/0x588
__debug_object_init+0x778/0x8b4
debug_object_init_on_stack+0x40/0x50
start_flush_work+0x16c/0x3f0
__flush_work+0xb8/0x124
flush_work+0x20/0x30
xlog_cil_force_lsn+0x88/0x204 [xfs]
xfs_log_force_lsn+0x128/0x1b8 [xfs]
xfs_file_fsync+0x3c4/0x488 [xfs]
vfs_fsync_range+0xb0/0xd0
generic_write_sync+0x80/0xa0 [xfs]
xfs_file_buffered_aio_write+0x66c/0x6e4 [xfs]
xfs_file_write_iter+0x1a0/0x218 [xfs]
__vfs_write+0x1cc/0x214
vfs_write+0x12c/0x1a4
ksys_write+0xb0/0x120
__arm64_sys_write+0x54/0x88
el0_svc_handler+0x170/0x240
el0_sync_handler+0x150/0x250
el0_sync+0x164/0x180

other info that might help us debug this:

Chain exists of:
&(&zone->lock)->rlock --> &(&port->lock)->rlock --> &pool->lock/1

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&pool->lock/1);
lock(&(&port->lock)->rlock);
lock(&pool->lock/1);
lock(&(&zone->lock)->rlock);

*** DEADLOCK ***

4 locks held by doio/49441:
#0: a0ff00886fc27408 (sb_writers#8){.+.+}, at: vfs_write+0x118/0x1a4
#1: 8fff00080810dfe0 (&xfs_nondir_ilock_class){++++}, at:
xfs_ilock+0x2a8/0x300 [xfs]
#2: ffff9000129f2390 (rcu_read_lock){....}, at:
rcu_lock_acquire+0x8/0x38
#3: 60ff000822352818 (&pool->lock/1){-.-.}, at:
start_flush_work+0xd8/0x3f0

stack backtrace:
CPU: 48 PID: 49441 Comm: doio Tainted: G W
Hardware name: HPE Apollo 70 /C01_APACHE_MB , BIOS
L50_5.13_1.11 06/18/2019
Call trace:
dump_backtrace+0x0/0x248
show_stack+0x20/0x2c
dump_stack+0xe8/0x150
print_circular_bug+0x368/0x380
check_noncircular+0x28c/0x294
validate_chain+0xf6c/0x2e2c
__lock_acquire+0x868/0xc2c
lock_acquire+0x320/0x360
_raw_spin_lock+0x64/0x80
rmqueue+0x138/0x2050
get_page_from_freelist+0x474/0x688
__alloc_pages_nodemask+0x3b4/0x18dc
alloc_pages_current+0xd0/0xe0
alloc_slab_page+0x2b4/0x5e0
new_slab+0xc8/0x6bc
___slab_alloc+0x3b8/0x640
kmem_cache_alloc+0x4b4/0x588
__debug_object_init+0x778/0x8b4
debug_object_init_on_stack+0x40/0x50
start_flush_work+0x16c/0x3f0
__flush_work+0xb8/0x124
flush_work+0x20/0x30
xlog_cil_force_lsn+0x88/0x204 [xfs]
xfs_log_force_lsn+0x128/0x1b8 [xfs]
xfs_file_fsync+0x3c4/0x488 [xfs]
vfs_fsync_range+0xb0/0xd0
generic_write_sync+0x80/0xa0 [xfs]
xfs_file_buffered_aio_write+0x66c/0x6e4 [xfs]
xfs_file_write_iter+0x1a0/0x218 [xfs]
__vfs_write+0x1cc/0x214
vfs_write+0x12c/0x1a4
ksys_write+0xb0/0x120
__arm64_sys_write+0x54/0x88
el0_svc_handler+0x170/0x240
el0_sync_handler+0x150/0x250
el0_sync+0x164/0x180

Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Signed-off-by: Qian Cai <cai@lca.pw>
Link: https://lore.kernel.org/r/1573679785-21068-1-git-send-email-cai@lca.pw
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/char/random.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index cda12933a17da..ea1973d358430 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1687,8 +1687,9 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller,
print_once = true;
#endif
if (__ratelimit(&unseeded_warning))
- pr_notice("random: %s called from %pS with crng_init=%d\n",
- func_name, caller, crng_init);
+ printk_deferred(KERN_NOTICE "random: %s called from %pS "
+ "with crng_init=%d\n", func_name, caller,
+ crng_init);
}

/*
--
2.20.1
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