linux-kernel - Re: [PATCH] block: fix refcounting in BLKBSZSET

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Message-ID: <AANLkTim6az_pR53LWzwP_KTe_=31awOKanYUZd_eJQkZ@mail.gmail.com>
Date:	Thu, 24 Feb 2011 16:20:31 +0100
From:	Florian Mickler <florian@...kler.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Mike Snitzer <snitzer@...hat.com>, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, kovariadam@...il.com, rjw@...k.pl,
	tj@...nel.org, linux-kernel@...r.kernel.org,
	Alasdair G Kergon <agk@...hat.com>, psusi@....rr.com
Subject: Re: [PATCH] block: fix refcounting in BLKBSZSET

Hi,

2011/2/24 Mike Snitzer <snitzer@...hat.com>:
> On Thu, Feb 24, 2011 at 9:48 AM, Miklos Szeredi <miklos@...redi.hu> wrote:
>> [and lkml cc-d too]
>>
>> This fixes bug 29202 in the 2.6.38 regression list.
>
> It looks like this may fix bug 29792 too.
>
> Mike
>
>> Please apply.
>>
>> Thanks,
>> Miklos
>>
>> ----
>> Subject: block: fix refcounting in BLKBSZSET
>>
>> From: Miklos Szeredi <mszeredi@...e.cz>
>>
>> Adam Kovari and others reported that disconnecting an USB drive with
>> an ntfs-3g filesystem would cause "kernel BUG at fs/inode.c:1421!" to
>> be triggered.
>>
>> The BUG could be traced back to ioctl(BLKBSZSET), which would
>> erroneously decrement the refcount on the bdev.  This is because
>> blkdev_get() expects the refcount to be already incremented and either
>> returns success or decrements the refcount and returns an error.
>>
>> The bug was introduced by e525fd89 (block: make blkdev_get/put()
>> handle exclusive access), which didn't take into account this behavior
>> of blkdev_get().
>>

putting a small reference to the bug reports in the changelog
(it is enough to have the bugnumber in there somewhere, grepping for 5
digit numbers doesn't turn up all too many false positives... )
helps with keeping track of the regressions and letting people know
that a fix / change was posted.

A line like "This fixes bug 29202." is sufficient.

Pasting a complete link( i.e.
https://bugzilla.kernel.org/show_bug.cgi?id=29202 ) would even allow
for an automated note in the bugzilla when it hits Linus tree.

Cheers,
Flo
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