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Date: Mon, 16 Jan 2012 10:53:32 +0800
From: Wu Fengguang <fengguang.wu@intel.com>
To: Rabin Vincent <rabin@rab.in>
Cc: Chanho Min <chanho0207@gmail.com>, Jens Axboe <axboe@kernel.dk>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/backing-dev.c: fix crash when USB/SCSI device is
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On Sun, Jan 15, 2012 at 09:11:07PM +0530, Rabin Vincent wrote:
> On Sun, Jan 15, 2012 at 08:58:53PM +0800, Wu Fengguang wrote:
> > On Sun, Jan 15, 2012 at 03:58:43PM +0530, Rabin Vincent wrote:
> > > diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> > > index 71034f4..a39ad70 100644
> > > --- a/mm/backing-dev.c
> > > +++ b/mm/backing-dev.c
> > > @@ -318,7 +318,7 @@ static void wakeup_timer_fn(unsigned long data)
> > >  	if (bdi->wb.task) {
> > >  		trace_writeback_wake_thread(bdi);
> > >  		wake_up_process(bdi->wb.task);
> > > -	} else {
> > > +	} else if (bdi->dev) {
> > >  		/*
> > >  		 * When bdi tasks are inactive for long time, they are killed.
> > >  		 * In this case we have to wake-up the forker thread which
> > > @@ -584,6 +584,8 @@ EXPORT_SYMBOL(bdi_register_dev);
> > >   */
> > >  static void bdi_wb_shutdown(struct backing_dev_info *bdi)
> > >  {
> > > +	struct task_struct *task = NULL;
> > 
> > NULL not necessary?
> 
> Will fix.
> 
> Also, I notice another problem here.  bdi->dev should be made NULL before the
> device is unregistered, not after:

Yes, good catch!

> 		if (!bdi_cap_flush_forker(bdi))
> 			bdi_wb_shutdown(bdi);
> 		bdi_debug_unregister(bdi);
> 		device_unregister(bdi->dev);
> 		bdi->dev = NULL;

Thanks,
Fengguang