Thursday, June 14, 2007

let's discuss Linux kernel programming here

As told by Dave today, the MIPS kernel stack dump doesn't dump the calling stack in order. It just dump all the seemly kernel functions in the stack. They could be functions called before the real BUG happened.

For example, the following call trace dump is not the real calling stack. The bug is in set_mctrl, which called spin_lock_irqsave, but the same lock was acquired by the caller of set_mctrl function already.

BUG: spinlock recursion on CPU#0, swapper/1
lock: 80302a84, .magic: dead4ead, .owner: swapper/1, .owner_cpu: 0
Call Trace:
[<801f03c8>] _raw_spin_lock+0x4c/0x154
[<802c2ef4>] _spin_lock_irqsave+0x40/0x58
[<80212bfc>] bcm1103serial_set_mctrl+0x70/0xb8
[<8012e934>] printk+0x1c/0x28
[<802123ac>] uart_add_one_port+0x290/0x354
[<80184320>] exact_match+0x0/0x8
[<80184328>] exact_lock+0x0/0x28
[<801ff9d4>] alloc_tty_driver+0x24/0x64
[<80212088>] uart_register_driver+0x194/0x1cc
[<80350000>] keypad_init+0x48/0x14c
[<80351020>] bcm1103serial_init+0x44/0x68
[<80100558>] init+0xc4/0x29c
[<80100558>] init+0xc4/0x29c
[<80109cd4>] kernel_thread_helper+0x10/0x18
[<80109cc4>] kernel_thread_helper+0x0/0x18

Remember, the call trace dump of MIPS is not the exact calling trace, you have to find clue in the functions dumped.