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From: Greg KH <gregkh@linuxfoundation.org>
To: Yu Kuai <yukuai3@huawei.com>
Cc: linux-block@vger.kernel.org, stable@vger.kernel.org,
	axboe@kernel.dk, hch@lst.de, yi.zhang@huawei.com
Subject: Re: [PATCH linux-4.19.y] blk-mq: fix divide by zero crash in tg_may_dispatch()
Date: Wed, 15 Sep 2021 13:27:39 +0200	[thread overview]
Message-ID: <YUHYqwVeeXtfD0qf@kroah.com> (raw)
In-Reply-To: <20210914125402.4068844-1-yukuai3@huawei.com>

On Tue, Sep 14, 2021 at 08:54:02PM +0800, Yu Kuai wrote:
> If blk-throttle is enabled and io is issued before
> blk_throtl_register_queue() is done. Divide by zero crash will be
> triggered in tg_may_dispatch() because 'throtl_slice' is uninitialized.
> 
> The problem is fixed in commit 75f4dca59694 ("block: call
> blk_register_queue earlier in device_add_disk") from mainline, however
> it's too hard to backport this patch due to lots of refactoring.
> 
> Thus introduce a new flag QUEUE_FLAG_THROTL_INIT_DONE. It will be set
> after blk_throtl_register_queue() is done, and will be checked before
> applying any config.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  block/blk-sysfs.c      |  2 ++
>  block/blk-throttle.c   | 41 +++++++++++++++++++++++++++++++++++++++--
>  include/linux/blkdev.h |  1 +
>  3 files changed, 42 insertions(+), 2 deletions(-)


The commit you reference above is in 5.15-rc1.  What about all of the
other stable kernel releases newer than 4.19.y?  You do not want to move
to a newer release and have a regression.

And I would _REALLY_ like to take the identical commits that are
upstream if at all possible.  What is needed to backport instead of
doing this one-off patch instead?

When we take changes that are not upstream, almost always they are
broken so we almost never want to do that.

thanks,

greg k-h

  reply	other threads:[~2021-09-15 11:27 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14 12:54 [PATCH linux-4.19.y] blk-mq: fix divide by zero crash in tg_may_dispatch() Yu Kuai
2021-09-15 11:27 ` Greg KH [this message]
2021-09-15 11:58   ` yukuai (C)

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