linux-kernel - Re: [PATCHv2] backing-dev: fix wakeup timer races with bdi

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Message-ID: <20120131132403.GA20016@localhost>
Date:	Tue, 31 Jan 2012 21:24:03 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Rabin Vincent <rabin@....in>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org, chanho0207@...il.com
Subject: Re: [PATCHv2] backing-dev: fix wakeup timer races with
 bdi_unregister()

On Thu, Jan 19, 2012 at 10:20:20PM +0530, Rabin Vincent wrote:
> While 7a401a972df8e18 ("backing-dev: ensure wakeup_timer is deleted")
> addressed the problem of the bdi being freed with a queued wakeup
> timer, there are other races that could happen if the wakeup timer
> expires after/during bdi_unregister(), before bdi_destroy() is called.
> 
> wakeup_timer_fn() could attempt to wakeup a task which has already has
> been freed, or could access a NULL bdi->dev via the wake_forker_thread
> tracepoint.
> 
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Wu Fengguang <fengguang.wu@...el.com>
> Reported-by: Chanho Min <chanho.min@....com>
> Signed-off-by: Rabin Vincent <rabin@....in>
> ---

Thanks. I just pushed it to linux-next, together with this related one:

        Subject: writeback: fix NULL bdi->dev in trace writeback_single_inode
        Date: Tue Jan 17 11:18:56 CST 2012

        bdi_prune_sb() resets sb->s_bdi to default_backing_dev_info when the
        tearing down the original bdi. Fix trace_writeback_single_inode to
        use sb->s_bdi=default_backing_dev_info rather than bdi->dev=NULL for a
        teared down bdi.

        Reported-by: Rabin Vincent <rabin@....in>
        Tested-by: Rabin Vincent <rabin@....in>
        Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>

Thanks,
Fengguang
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