linux-kernel - Re: help! locks problem in block layer request queue?

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Date:	Thu, 19 Feb 2009 14:13:05 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	"Gao, Yunpeng" <yunpeng.gao@...el.com>
Cc:	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: help! locks problem in block layer request queue?

On Thu, Feb 19 2009, Gao, Yunpeng wrote:
> 
> Hi all,
> 
> Sorry for the too long email. But I encountered a kernle OOP problem
> when testing my standalone NAND block driver (it's almost a normal
> block device driver) and not sure why this happen.
> 
> In my development environment, the linux 2.6.27 kernel boot with
> initrd, then 'chroot' to an MMC card. After chroot, I try to mkfs.ext3
> on NAND device. but it caused the kernel OOP message.  If I mkfs.ext3
> on NAND device before chroot, then it works well (it can mount/umount,
> copy file correctly accross system reboot).
> 
> Below is the log message (/dev/mmcblk0 is the MMC card device node,
> and /dev/nda is the NAND flash device node) and part of the driver
> code.
> 
> From the OOP message, It seems there's improper usage of locks in my
> driver code, but actually, there only one spinlock used in the driver
> (spinlock_t qlock defined in struct spectra_nand_dev). And it only
> used by registered request queue. Also, I used a semaphore
> ('spectra_sem') to prevent the low layer function from being
> re-entered. As the low layer (hardware layer) now works in PIO mode
> and it's very slowly, so maybe it holds the spinlock or semaphore for
> too long time?

You call the bvec_kmap_irq() and then call a function that does a
down(). This is illegal, as you cannot block/schedule with interrupts
disabled.

-- 
Jens Axboe

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