linux-kernel - Re: [PATCH 1/2] staging: zram: minimize `slot_free

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Date:	Mon, 9 Sep 2013 11:33:27 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Jerome Marchand <jmarchan@...hat.com>, devel@...verdev.osuosl.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH 1/2] staging: zram: minimize `slot_free_lock' usage

On Fri, Sep 06, 2013 at 05:55:45PM +0300, Sergey Senozhatsky wrote:
> On (09/06/13 16:42), Jerome Marchand wrote:
> > On 09/06/2013 03:47 PM, Sergey Senozhatsky wrote:
> > > Calling handle_pending_slot_free() for every RW operation may
> > > cause unneccessary slot_free_lock locking, because most likely
> > > process will see NULL slot_free_rq. handle_pending_slot_free()
> > > only when current detects that slot_free_rq is not NULL.
> > > 
> > > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> > > 
> > > ---
> > > 
> > >  drivers/staging/zram/zram_drv.c | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
> > > index 91d94b5..17386e2 100644
> > > --- a/drivers/staging/zram/zram_drv.c
> > > +++ b/drivers/staging/zram/zram_drv.c
> > > @@ -532,14 +532,15 @@ static int zram_bvec_rw(struct zram *zram, struct bio_vec *bvec, u32 index,
> > >  {
> > >  	int ret;
> > >  
> > > +	if (zram->slot_free_rq)
> > > +		handle_pending_slot_free(zram);
> > > +
> > 
> > Calling handle_pending_slot_free() without holding zram->lock?
> > That's racy.
> 
> sorry, my bad. it should take down_write() lock.
> 

Or down_read() on the read path.  We leave the original as-is?

regards,
dan carpenter

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