linux-kernel - Re: 2.6.20 kernel hang with USB drive and vfat doing ftruncate

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Message-Id: <92CB3192-9176-4D30-B818-16A9C979F5E9@kernel.crashing.org>
Date:	Fri, 16 Feb 2007 23:05:43 -0600
From:	Kumar Gala <galak@...nel.crashing.org>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.20 kernel hang with USB drive and vfat doing ftruncate


On Feb 16, 2007, at 5:10 PM, Robert Hancock wrote:

> Kumar Gala wrote:
>> I'm seeing an issue with a stock 2.6.20 kernel running on an  
>> embedded PPC.  I've got a usb flash drive plugged in and the  
>> filesystem on the drive is vfat.  Running with 64M and no swap.
>> If I execute a series of large (100M+) ftruncate() on the disk the  
>> kernel will hang and never return.  It seems to be stuck in the  
>> idle loop().
>
> On FAT filesystems this forces the entire file contents of that  
> size to be written out with zeros. Are you sure the kernel just  
> isn't busy writing out all that data to the disk?

I'm pretty sure, seeing as if I run the test it takes maybe 20-30  
seconds to create the file if it succeeds.  However, I've weighted 10  
minutes and still no prompt.

I'm also able to break in with a HW debugger and am always in the  
idle loop.

- k
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