Re: Question on Schedule and Preemption

[Steven Rostedt <rostedt@kihontech.com>]

On Tue, 2006-04-18 at 20:55 +0800, Liu haixiang wrote:
> Hi Andreas Mohr,
> 
> Thanks for your explanation. And now I am clear on above code.
> 
> Please see my problem below. It seemed that there is one code to add
> preempt count [<8440de20>], which means that the kernel can not be
> preemptied. Then the code call switch_to (which contains the code
> __switch_to_end).

Your stack trace looks fishy, I recommend doing a "make menuconfig", go
to "Kernel Hacking" and turn on "Compile the kernel with frame pointers"
This will give you a better and cleaner stack dump.

> 
> And it's problem becuase the code already in the atomic status and can
> not be scheduled.
> 
> My understanding is correct? And how to know which process or code
> call add_preempt_count? Is there any good way to find the clue?

Well according to your output, it was the task "TURNER0" with the pid
611.  After you recompile the kernel with CONFIG_FRAME_POINTERS you will
need to follow the stack trace and see what function turned off
preemption.  This can happen calling a spin_lock and not unlocking it
before calling something that would schedule.

If you also turn on in "Kernel Hacking" -> "Compile the kernel with
debug info", you can then do a "gdb vmlinux" in the root directory of
the compile, and pass in the stack address with the command 
"li *0xc042382e" to show where that function would return. (replace the
c042382e with the location you are looking for).

Also, what arch are you using to get a 0x04000000 in the preempt_count
(the 0x1 is the depth). Of course I'm looking at 2.6.17-rc1 and not the
one you are using.  Hmm, your arch may not even support frame pointers.

-- Steve

> 
> ===================================
> scheduling while atomic: TUNER0/0x04000001/611
> 
> Call trace:
> [<846532b4>] __switch_to_end+0x2fe/0x38a
> [<8440de20>] add_preempt_count+0x0/0xa0
> [<84652c80>] schedule+0x0/0x300
> [<8440dd80>] sub_preempt_count+0x0/0xa0
> [<84653ef8>] cond_resched+0x38/0x80
> [<84405096>] ret_from_irq+0x0/0x12
> [<845145e0>] __delay+0x0/0x20
> [<84653ef8>] cond_resched+0x38/0x80
> [<8440de20>] add_preempt_count+0x0/0xa0
> [<84652c80>] schedule+0x0/0x300
> [<8440dd80>] sub_preempt_count+0x0/0xa0
> [<845d9a16>] bit_xfer+0x256/0x8c0
> [<845d6d36>] i2c_transfer+0x56/0xe0
> [<c042382e>] STI2C_Read+0x2e/0x80 [sti2c_ioctl]
> [<c046af32>] I2C_ReadWrite+0x72/0x1a0 [sttuner_core]
> [<c0487d7c>] IOARCH_Handle+0x10/0xffff49a0 [sttuner_core]
> [<84653ec0>] cond_resched+0x0/0x80
> [<845d9cac>] bit_xfer+0x4ec/0x8c0
> [<c046b398>] IOARCH_ReadWrite+0x118/0x180 [sttuner_core]
> [<c05cb000>] 0xc05cb000
> [<c046b456>] STTUNER_IOARCH_ReadWrite+0x16/0x40 [sttuner_core]
> [<c05c300c>] 0xc05c300c
> [<c0477482>] STTUNER_IOREG_GetContigousRegisters+0x142/0x1c0 [sttuner_core]
> [<c046fd1a>] Drv0299_GetNoiseEstimator+0x1a/0x120 [sttuner_core]
> [<c04835f0>] STTUNER_DrvInst+0x0/0xffff911c [sttuner_core]
> [<c0483798>] STTUNER_DrvInst+0x1a8/0xffff911c [sttuner_core]
> [<c048379c>] STTUNER_DrvInst+0x1ac/0xffff911c [sttuner_core]
> [<c048379c>] STTUNER_DrvInst+0x1ac/0xffff911c [sttuner_core]
> [<c05c300c>] 0xc05c300c
> [<c05c3000>] 0xc05c3000
> [<c0470960>] demod_d0299_GetSignalQuality+0x20/0x40 [sttuner_core]
> [<c048379c>] STTUNER_DrvInst+0x1ac/0xffff911c [sttuner_core]
> [<c0483798>] STTUNER_DrvInst+0x1a8/0xffff911c [sttuner_core]
> [<c05c3000>] 0xc05c3000
> [<c046c826>] SATTASK_GetTunerInfo+0x46/0xe0 [sttuner_core]
> [<c04835f0>] STTUNER_DrvInst+0x0/0xffff911c [sttuner_core]
> [<c04837ac>] STTUNER_DrvInst+0x1bc/0xffff911c [sttuner_core]
> [<c046c9fa>] SATTASK_ProcessTracking+0x13a/0x1c0 [sttuner_core]
> [<c04835f0>] STTUNER_DrvInst+0x0/0xffff911c [sttuner_core]
> [<c04835f0>] STTUNER_DrvInst+0x0/0xffff911c [sttuner_core]
> [<c046d388>] SATTASK_ScanTask+0x3e8/0x620 [sttuner_core]
> [<c046ca80>] SATTASK_ProcessScanExact+0x0/0x340 [sttuner_core]
> [<c0483800>] STTUNER_DrvInst+0x210/0xffff911c [sttuner_core]
> [<c04835f0>] STTUNER_DrvInst+0x0/0xffff911c [sttuner_core]
> [<c048482c>] STTUNER_DrvInst+0x123c/0xffff911c [sttuner_core]
> [<c048492c>] STTUNER_DrvInst+0x133c/0xffff911c [sttuner_core]
> [<c04835f0>] STTUNER_DrvInst+0x0/0xffff911c [sttuner_core]
> [<c04836ec>] STTUNER_DrvInst+0xfc/0xffff911c [sttuner_core]
> [<c04836ec>] STTUNER_DrvInst+0xfc/0xffff911c [sttuner_core]
> [<c04848ec>] STTUNER_DrvInst+0x12fc/0xffff911c [sttuner_core]
> [<c04848ec>] STTUNER_DrvInst+0x12fc/0xffff911c [sttuner_core]
> [<c048492c>] STTUNER_DrvInst+0x133c/0xffff911c [sttuner_core]
> [<8442b4e4>] kthread+0xe4/0x140
> [<c046cfa0>] SATTASK_ScanTask+0x0/0x620 [sttuner_core]
> [<c0483800>] STTUNER_DrvInst+0x210/0xffff911c [sttuner_core]
> [<8440f4a0>] complete+0x0/0xc0
> [<8442b3e0>] kthread_should_stop+0x0/0x20
> [<84403004>] kernel_thread_helper+0x4/0x20
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-- 
Steven Rostedt
Senior Programmer
Kihon Technologies
(607)786-4830

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