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Subject[PATCH 4.9 102/329] irqchip/gic-v3: Change pr_debug message to pr_devel
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Salter <msalter@redhat.com>

[ Upstream commit b6dd4d83dc2f78cebc9a7e6e7e4bc2be4d29b94d ]

The pr_debug() in gic-v3 gic_send_sgi() can trigger a circular locking
warning:

GICv3: CPU10: ICC_SGI1R_EL1 5000400
======================================================
WARNING: possible circular locking dependency detected
4.15.0+ #1 Tainted: G W
------------------------------------------------------
dynamic_debug01/1873 is trying to acquire lock:
((console_sem).lock){-...}, at: [<0000000099c891ec>] down_trylock+0x20/0x4c

but task is already holding lock:
(&rq->lock){-.-.}, at: [<00000000842e1587>] __task_rq_lock+0x54/0xdc

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&rq->lock){-.-.}:
__lock_acquire+0x3b4/0x6e0
lock_acquire+0xf4/0x2a8
_raw_spin_lock+0x4c/0x60
task_fork_fair+0x3c/0x148
sched_fork+0x10c/0x214
copy_process.isra.32.part.33+0x4e8/0x14f0
_do_fork+0xe8/0x78c
kernel_thread+0x48/0x54
rest_init+0x34/0x2a4
start_kernel+0x45c/0x488

-> #1 (&p->pi_lock){-.-.}:
__lock_acquire+0x3b4/0x6e0
lock_acquire+0xf4/0x2a8
_raw_spin_lock_irqsave+0x58/0x70
try_to_wake_up+0x48/0x600
wake_up_process+0x28/0x34
__up.isra.0+0x60/0x6c
up+0x60/0x68
__up_console_sem+0x4c/0x7c
console_unlock+0x328/0x634
vprintk_emit+0x25c/0x390
dev_vprintk_emit+0xc4/0x1fc
dev_printk_emit+0x88/0xa8
__dev_printk+0x58/0x9c
_dev_info+0x84/0xa8
usb_new_device+0x100/0x474
hub_port_connect+0x280/0x92c
hub_event+0x740/0xa84
process_one_work+0x240/0x70c
worker_thread+0x60/0x400
kthread+0x110/0x13c
ret_from_fork+0x10/0x18

-> #0 ((console_sem).lock){-...}:
validate_chain.isra.34+0x6e4/0xa20
__lock_acquire+0x3b4/0x6e0
lock_acquire+0xf4/0x2a8
_raw_spin_lock_irqsave+0x58/0x70
down_trylock+0x20/0x4c
__down_trylock_console_sem+0x3c/0x9c
console_trylock+0x20/0xb0
vprintk_emit+0x254/0x390
vprintk_default+0x58/0x90
vprintk_func+0xbc/0x164
printk+0x80/0xa0
__dynamic_pr_debug+0x84/0xac
gic_raise_softirq+0x184/0x18c
smp_cross_call+0xac/0x218
smp_send_reschedule+0x3c/0x48
resched_curr+0x60/0x9c
check_preempt_curr+0x70/0xdc
wake_up_new_task+0x310/0x470
_do_fork+0x188/0x78c
SyS_clone+0x44/0x50
__sys_trace_return+0x0/0x4

other info that might help us debug this:

Chain exists of:
(console_sem).lock --> &p->pi_lock --> &rq->lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&rq->lock);
lock(&p->pi_lock);
lock(&rq->lock);
lock((console_sem).lock);

*** DEADLOCK ***

2 locks held by dynamic_debug01/1873:
#0: (&p->pi_lock){-.-.}, at: [<000000001366df53>] wake_up_new_task+0x40/0x470
#1: (&rq->lock){-.-.}, at: [<00000000842e1587>] __task_rq_lock+0x54/0xdc

stack backtrace:
CPU: 10 PID: 1873 Comm: dynamic_debug01 Tainted: G W 4.15.0+ #1
Hardware name: GIGABYTE R120-T34-00/MT30-GS2-00, BIOS T48 10/02/2017
Call trace:
dump_backtrace+0x0/0x188
show_stack+0x24/0x2c
dump_stack+0xa4/0xe0
print_circular_bug.isra.31+0x29c/0x2b8
check_prev_add.constprop.39+0x6c8/0x6dc
validate_chain.isra.34+0x6e4/0xa20
__lock_acquire+0x3b4/0x6e0
lock_acquire+0xf4/0x2a8
_raw_spin_lock_irqsave+0x58/0x70
down_trylock+0x20/0x4c
__down_trylock_console_sem+0x3c/0x9c
console_trylock+0x20/0xb0
vprintk_emit+0x254/0x390
vprintk_default+0x58/0x90
vprintk_func+0xbc/0x164
printk+0x80/0xa0
__dynamic_pr_debug+0x84/0xac
gic_raise_softirq+0x184/0x18c
smp_cross_call+0xac/0x218
smp_send_reschedule+0x3c/0x48
resched_curr+0x60/0x9c
check_preempt_curr+0x70/0xdc
wake_up_new_task+0x310/0x470
_do_fork+0x188/0x78c
SyS_clone+0x44/0x50
__sys_trace_return+0x0/0x4
GICv3: CPU0: ICC_SGI1R_EL1 12000

This could be fixed with printk_deferred() but that might lessen its
usefulness for debugging. So change it to pr_devel to keep it out of
production kernels. Developers working on gic-v3 can enable it as
needed in their kernels.

Signed-off-by: Mark Salter <msalter@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/irqchip/irq-gic-v3.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/irqchip/irq-gic-v3.c
+++ b/drivers/irqchip/irq-gic-v3.c
@@ -601,7 +601,7 @@ static void gic_send_sgi(u64 cluster_id,
MPIDR_TO_SGI_AFFINITY(cluster_id, 1) |
tlist << ICC_SGI1R_TARGET_LIST_SHIFT);

- pr_debug("CPU%d: ICC_SGI1R_EL1 %llx\n", smp_processor_id(), val);
+ pr_devel("CPU%d: ICC_SGI1R_EL1 %llx\n", smp_processor_id(), val);
gic_write_sgi1r(val);
}


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