[PATCH] x86: Fixup lockdep complaint caused by io apic code

Jan Kara
2014-10-10T14:24:14Z

0day kernel testing guys have reported following lockdep complaint:
======================================================
[ INFO: possible circular locking dependency detected ]
3.15.0-rc5-00567-gbafe980 #1 Not tainted
-------------------------------------------------------
swapper/1 is trying to acquire lock:
(&irq_desc_lock_class){-.-...}, at: [<8107dc8c>] __irq_get_desc_lock+0x3c/0x70

but task is already holding lock:
(&port_lock_key){......}, at: [<815f5b27>] serial8250_startup+0x337/0x720

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 (&port_lock_key){......}:
<this stack looks somewhat bogus but we do end up taking
port->lock when printing to serial console>
[<810750e5>] lock_acquire+0x85/0x190
[<81baed9d>] _raw_spin_lock_irqsave+0x4d/0x60
[<8106eb1c>] down_trylock+0xc/0x30
[<8107b795>] console_trylock+0x15/0xb0
[<8107be8f>] vprintk_emit+0x14f/0x4d0
[<81b969b9>] printk+0x38/0x3a
[<82137f78>] print_ICs+0x5b/0x3e7
[<8212bb41>] do_one_initcall+0x8b/0x128
[<8212bd7d>] kernel_init_freeable+0x19f/0x236
[<81b9238b>] kernel_init+0xb/0xd0
[<81bb0080>] ret_from_kernel_thread+0x20/0x30

-> #1 (i8259A_lock){-.....}:
[<810750e5>] lock_acquire+0x85/0x190
[<81baed9d>] _raw_spin_lock_irqsave+0x4d/0x60
[<81005af1>] unmask_8259A_irq+0x11/0x60
[<81005b4b>] enable_8259A_irq+0xb/0x10
[<8107fffb>] irq_enable+0x2b/0x40
[<8108005d>] irq_startup+0x4d/0x60
[<8107f2bc>] __setup_irq+0x39c/0x460
[<8107f433>] setup_irq+0x33/0x80
[<8212db15>] setup_default_timer_irq+0xf/0x11
[<8212db2d>] hpet_time_init+0x16/0x18
[<8212daff>] x86_late_time_init+0x9/0x10
[<8212ba3d>] start_kernel+0x331/0x3aa
[<8212b380>] i386_start_kernel+0x12e/0x131

-> #0 (&irq_desc_lock_class){-.-...}:
[<810743c2>] __lock_acquire+0x19c2/0x1b20
[<810750e5>] lock_acquire+0x85/0x190
[<81baed9d>] _raw_spin_lock_irqsave+0x4d/0x60
[<8107dc8c>] __irq_get_desc_lock+0x3c/0x70
[<8107eb1e>] __disable_irq_nosync+0x1e/0x50
[<8107eb58>] disable_irq_nosync+0x8/0x10
[<815f5c78>] serial8250_startup+0x488/0x720
[<815f205e>] uart_startup.part.4+0x6e/0x1e0
[<815f2a40>] uart_open+0xe0/0x140
[<815e4b51>] tty_open+0x141/0x510
[<81118bc0>] chrdev_open+0x60/0x140
[<8111372c>] do_dentry_open+0x14c/0x230
[<8111459e>] finish_open+0x2e/0x40
[<8112132a>] do_last+0x4aa/0xd30
[<81121c5a>] path_openat+0xaa/0x610
[<811221ec>] do_filp_open+0x2c/0x70
[<81114a81>] do_sys_open+0x111/0x210
[<81114b9d>] SyS_open+0x1d/0x20
[<8212bda4>] kernel_init_freeable+0x1c6/0x236
[<81b9238b>] kernel_init+0xb/0xd0
[<81bb0080>] ret_from_kernel_thread+0x20/0x30

I believe the core of the problem is that print_PIC() calls printk()
from under i8259A_lock. I've checked and that doesn't seem to happen
anywhere else in the kernel. So let's move printk() from under that
lock.

As a side note this problem has existed for a long time but it was
uncovered by my patch resulting in extended lockdep coverage of printk
code.

Reported-by: Jet Chen <jet.chen@intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
arch/x86/kernel/apic/io_apic.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index 6ad4658de705..b815a4c9e5e5 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -1770,7 +1770,7 @@ __apicdebuginit(void) print_local_APICs(int maxcpu)

__apicdebuginit(void) print_PIC(void)
{
- unsigned int v;
+ unsigned int v0, v1, v2;
unsigned long flags;

if (!legacy_pic->nr_legacy_irqs)
@@ -1780,24 +1780,23 @@ __apicdebuginit(void) print_PIC(void)

raw_spin_lock_irqsave(&i8259A_lock, flags);

- v = inb(0xa1) << 8 | inb(0x21);
- printk(KERN_DEBUG "... PIC IMR: %04x\n", v);
-
- v = inb(0xa0) << 8 | inb(0x20);
- printk(KERN_DEBUG "... PIC IRR: %04x\n", v);
+ v0 = inb(0xa1) << 8 | inb(0x21);
+ v1 = inb(0xa0) << 8 | inb(0x20);

outb(0x0b,0xa0);
outb(0x0b,0x20);
- v = inb(0xa0) << 8 | inb(0x20);
+ v2 = inb(0xa0) << 8 | inb(0x20);
outb(0x0a,0xa0);
outb(0x0a,0x20);

raw_spin_unlock_irqrestore(&i8259A_lock, flags);

- printk(KERN_DEBUG "... PIC ISR: %04x\n", v);
+ printk(KERN_DEBUG "... PIC IMR: %04x\n", v0);
+ printk(KERN_DEBUG "... PIC IRR: %04x\n", v1);
+ printk(KERN_DEBUG "... PIC ISR: %04x\n", v2);

- v = inb(0x4d1) << 8 | inb(0x4d0);
- printk(KERN_DEBUG "... PIC ELCR: %04x\n", v);
+ v0 = inb(0x4d1) << 8 | inb(0x4d0);
+ printk(KERN_DEBUG "... PIC ELCR: %04x\n", v0);
}

static int __initdata show_lapic = 1;