linux-kernel - Re: [PATCH] fs: Fix mod_timer crash when removing USB sticks

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Date:	Thu, 22 Mar 2012 09:15:32 -0700
From:	Paul Taysom <taysom@...gle.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Mandeep Singh Baines <msb@...omium.org>,
	"Ted Ts'o" <tytso@....edu>, Theodore Tso <tytso@...gle.com>,
	Greg KH <greg@...ah.com>, Paul Taysom <taysom@...omium.org>,
	Jens Axboe <axboe@...nel.dk>, Andrew Morton <akpm@...gle.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, stable@...nel.org
Subject: Re: [PATCH] fs: Fix mod_timer crash when removing USB sticks

On Mon, Mar 19, 2012 at 7:02 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Mon, 19 Mar 2012, Paul Taysom wrote:
>
>> I have rerun my tests without my change on the 3.2.7 kernel and I was
>> not able to get it to crash. I even put some code in to do the early
>> detection so I didn't have to wait for another thread to stumble
>> across the corruption. The way I test is with several flash drivers
>> with ext2, ext3, ext4, FAT, and HPFS file systems and just repeatedly
>> plug and unplug them. When a flash drive is plugged in with a file
>> system, it is automatically mounted.
>
> That's not the right way to test a race like this.  The right way is to
> insert ssleep() calls at some appropriate spots, so that you can force
> the race to come out the way you want every time.
>
> What about the question of resetting the bdi pointer at the same time
> as some other thread is using it?  Have you tested whether Mandeep's
> locking suggestion will prevent problems?
>
> Alan Stern
>

The checks I added to timer.c seems to the defect every time. With
3.2.7, it never sees the defect.
Paul Taysom
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