Re: [PATCH 3/3] nilfs2: change sc_timer from a pointer to an embedded one in struct nilfs_sc_info

[Li Hong <lihong.hi-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

OK, I will improve this patch.

Thanks very much,
Li Hong

On Sun, Apr 11, 2010 at 11:40:22AM +0900, Ryusuke Konishi wrote:
> Hi,
> On Sun, 11 Apr 2010 00:17:52 +0800, Li Hong <lihong.hi-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > In nilfs_segctor_thread(), timer is a local variable allocated on stack. Its
> > address can't be set to sci->sc_timer and passed in several procedures.
> > 
> > It works now by chance, just because other procedures are called by
> > nilfs_segctor_thread() directly or indirectly and the stack hasn't been
> > deallocated yet.
> > 
> > Signed-off-by: Li Hong <lihong.hi-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> 
> Looks to be heading in the right direction.
> 
> Note that the del_timer_sync call in nilfs_segctor_thread() should be
> moved into nilfs_segctor_destroy() for safety.  Without the check if
> sci->sc_timer != NULL, sci->sc_timer can be registered to the timer
> list after the segment constructor thread died.  This leads to
> corruption of the timer list.
> 
> add_timer(&sci->sc_timer) is called only while nilfs->ns_segctor_sem
> (i.e. nilfs_transaction_lock) is held.
> 
> So, the place where del_timer_sync should be inserted, seems between
> 
>   down_write(&sbi->s_nilfs->ns_segctor_sem)
> 
> and
> 
>   kfree()
> 
> in nilfs_segctor_destroy().
> 
> Thanks,
> Ryusuke Konishi
> 
> > ---
> >  fs/nilfs2/segment.c |   31 +++++++++++++------------------
> >  fs/nilfs2/segment.h |    2 +-
> >  2 files changed, 14 insertions(+), 19 deletions(-)
> > 
> > diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
> > index dd3c4d5..310979a 100644
> > --- a/fs/nilfs2/segment.c
> > +++ b/fs/nilfs2/segment.c
> > @@ -2158,9 +2158,9 @@ static int nilfs_segctor_do_construct(struct nilfs_sc_info *sci, int mode)
> >  static void nilfs_segctor_start_timer(struct nilfs_sc_info *sci)
> >  {
> >  	spin_lock(&sci->sc_state_lock);
> > -	if (sci->sc_timer && !(sci->sc_state & NILFS_SEGCTOR_COMMIT)) {
> > -		sci->sc_timer->expires = jiffies + sci->sc_interval;
> > -		add_timer(sci->sc_timer);
> > +	if (!(sci->sc_state & NILFS_SEGCTOR_COMMIT)) {
> > +		sci->sc_timer.expires = jiffies + sci->sc_interval;
> > +		add_timer(&sci->sc_timer);
> >  		sci->sc_state |= NILFS_SEGCTOR_COMMIT;
> >  	}
> >  	spin_unlock(&sci->sc_state_lock);
> > @@ -2365,9 +2365,7 @@ static void nilfs_segctor_accept(struct nilfs_sc_info *sci)
> >  	spin_lock(&sci->sc_state_lock);
> >  	sci->sc_seq_accepted = sci->sc_seq_request;
> >  	spin_unlock(&sci->sc_state_lock);
> > -
> > -	if (sci->sc_timer)
> > -		del_timer_sync(sci->sc_timer);
> > +	del_timer_sync(&sci->sc_timer);
> >  }
> >  
> >  /**
> > @@ -2393,9 +2391,9 @@ static void nilfs_segctor_notify(struct nilfs_sc_info *sci, int mode, int err)
> >  			sci->sc_flush_request &= ~FLUSH_DAT_BIT;
> >  
> >  		/* re-enable timer if checkpoint creation was not done */
> > -		if (sci->sc_timer && (sci->sc_state & NILFS_SEGCTOR_COMMIT) &&
> > -		    time_before(jiffies, sci->sc_timer->expires))
> > -			add_timer(sci->sc_timer);
> > +		if ((sci->sc_state & NILFS_SEGCTOR_COMMIT) &&
> > +		    time_before(jiffies, sci->sc_timer.expires))
> > +			add_timer(&sci->sc_timer);
> >  	}
> >  	spin_unlock(&sci->sc_state_lock);
> >  }
> > @@ -2574,13 +2572,10 @@ static int nilfs_segctor_thread(void *arg)
> >  {
> >  	struct nilfs_sc_info *sci = (struct nilfs_sc_info *)arg;
> >  	struct the_nilfs *nilfs = sci->sc_sbi->s_nilfs;
> > -	struct timer_list timer;
> >  	int timeout = 0;
> >  
> > -	init_timer(&timer);
> > -	timer.data = (unsigned long)current;
> > -	timer.function = nilfs_construction_timeout;
> > -	sci->sc_timer = &timer;
> > +	sci->sc_timer.data = (unsigned long)current;
> > +	sci->sc_timer.function = nilfs_construction_timeout;
> >  
> >  	/* start sync. */
> >  	sci->sc_task = current;
> > @@ -2629,7 +2624,7 @@ static int nilfs_segctor_thread(void *arg)
> >  			should_sleep = 0;
> >  		else if (sci->sc_state & NILFS_SEGCTOR_COMMIT)
> >  			should_sleep = time_before(jiffies,
> > -						   sci->sc_timer->expires);
> > +					sci->sc_timer.expires);
> >  
> >  		if (should_sleep) {
> >  			spin_unlock(&sci->sc_state_lock);
> > @@ -2638,7 +2633,7 @@ static int nilfs_segctor_thread(void *arg)
> >  		}
> >  		finish_wait(&sci->sc_wait_daemon, &wait);
> >  		timeout = ((sci->sc_state & NILFS_SEGCTOR_COMMIT) &&
> > -			   time_after_eq(jiffies, sci->sc_timer->expires));
> > +			   time_after_eq(jiffies, sci->sc_timer.expires));
> >  
> >  		if (nilfs_sb_dirty(nilfs) && nilfs_sb_need_update(nilfs))
> >  			set_nilfs_discontinued(nilfs);
> > @@ -2647,8 +2642,7 @@ static int nilfs_segctor_thread(void *arg)
> >  
> >   end_thread:
> >  	spin_unlock(&sci->sc_state_lock);
> > -	del_timer_sync(sci->sc_timer);
> > -	sci->sc_timer = NULL;
> > +	del_timer_sync(&sci->sc_timer);
> >  
> >  	/* end sync. */
> >  	sci->sc_task = NULL;
> > @@ -2707,6 +2701,7 @@ static struct nilfs_sc_info *nilfs_segctor_new(struct nilfs_sb_info *sbi)
> >  	INIT_LIST_HEAD(&sci->sc_write_logs);
> >  	INIT_LIST_HEAD(&sci->sc_gc_inodes);
> >  	INIT_LIST_HEAD(&sci->sc_copied_buffers);
> > +	init_timer(&sci->sc_timer);
> >  
> >  	sci->sc_interval = HZ * NILFS_SC_DEFAULT_TIMEOUT;
> >  	sci->sc_mjcp_freq = HZ * NILFS_SC_DEFAULT_SR_FREQ;
> > diff --git a/fs/nilfs2/segment.h b/fs/nilfs2/segment.h
> > index 7aca765..dca1423 100644
> > --- a/fs/nilfs2/segment.h
> > +++ b/fs/nilfs2/segment.h
> > @@ -177,7 +177,7 @@ struct nilfs_sc_info {
> >  	unsigned long		sc_lseg_stime;	/* in 1/HZ seconds */
> >  	unsigned long		sc_watermark;
> >  
> > -	struct timer_list      *sc_timer;
> > +	struct timer_list	sc_timer;
> >  	struct task_struct     *sc_task;
> >  };
> >  
> > -- 
> > 1.6.3.3
> > 
> > --
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