linux-kernel - Re: [PATCH] mm/backing-dev.c: fix crash when USB/SCSI device is detached

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Date:	Mon, 16 Jan 2012 13:50:44 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Chanho Min <chanho0207@...il.com>
Cc:	Rabin Vincent <rabin@....in>, Jens Axboe <axboe@...nel.dk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/backing-dev.c: fix crash when USB/SCSI device is
 detached

On Mon, Jan 16, 2012 at 02:28:30PM +0900, Chanho Min wrote:
> On Mon, Jan 16, 2012 at 11:53 AM, Wu Fengguang <fengguang.wu@...el.com> wrote:
> > 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;
> 
> Thanks, I fully understand.
> In addition, Would not bdi_wakeup_flusher also be fixed?

Yes, indeed!

Thanks,
Fengguang

> >From dc7d4e86911c0a7ea35043485b04e8a09aa74ffd Mon Sep 17 00:00:00 2001
> From: Chanho Min <chanho.min@....com>
> Date: Mon, 16 Jan 2012 14:14:48 +0900
> Subject: [PATCH] backing-dev: add for 'fix wakeup timer races with
> bdi_unregister()'
> 
> Signed-off-by: Chanho Min <chanho.min@....com>
> ---
>  fs/fs-writeback.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index f855916..ee40833 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -97,7 +97,7 @@ static void bdi_wakeup_flusher(struct backing_dev_info *bdi)
>  {
>         if (bdi->wb.task) {
>                 wake_up_process(bdi->wb.task);
> -       } else {
> +       } else if (bdi->dev) {
>                 /*
>                  * The bdi thread isn't there, wake up the forker thread which
>                  * will create and run it.
> -- 
> 1.7.0.4
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