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

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Message-ID: <20130906145545.GC2238@swordfish.minsk.epam.com>
Date:	Fri, 6 Sep 2013 17:55:45 +0300
From:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Minchan Kim <minchan@...nel.org>, devel@...verdev.osuosl.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] staging: zram: minimize `slot_free_lock' usage

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.

	-ss

> Jerome
> 
> >  	if (rw == READ) {
> >  		down_read(&zram->lock);
> > -		handle_pending_slot_free(zram);
> >  		ret = zram_bvec_read(zram, bvec, index, offset, bio);
> >  		up_read(&zram->lock);
> >  	} else {
> >  		down_write(&zram->lock);
> > -		handle_pending_slot_free(zram);
> >  		ret = zram_bvec_write(zram, bvec, index, offset);
> >  		up_write(&zram->lock);
> >  	}
> > 
> > --
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> > 
> 
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