linux-kernel - RE: [PATCH] cfi: fix deadloop in cfi_cmdset_0002.c do_write

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Date:   Tue, 5 Feb 2019 22:28:44 +0000
From:   "Sobon, Przemyslaw" <psobon@...zon.com>
To:     Boris Brezillon <bbrezillon@...nel.org>,
        Liu Jian <liujian56@...wei.com>,
        "ikegami@...ied-telesis.co.jp" <ikegami@...ied-telesis.co.jp>
CC:     "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "computersforpeace@...il.com" <computersforpeace@...il.com>,
        "marek.vasut@...il.com" <marek.vasut@...il.com>,
        "richard@....at" <richard@....at>,
        "joakim.tjernlund@...inera.com" <joakim.tjernlund@...inera.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer

> From: Boris Brezillon <bbrezillon@...nel.org> 
> Sent: Sunday, February 3, 2019 12:35 AM
> > +Przemyslaw
> > 
> > On Fri, 1 Feb 2019 07:30:39 +0800
> > Liu Jian <liujian56@...wei.com> wrote:
> > 
> > > In function do_write_buffer(), in the for loop, there is a case
> > > chip_ready() returns 1 while chip_good() returns 0, so it never 
> > > break the loop.
> > > To fix this, chip_good() is enough and it should timeout if it stay 
> > > bad for a while.
> > 
> > Looks like Przemyslaw reported and fixed the same problem.
> > 
> > > 
> > > Fixes: dfeae1073583(mtd: cfi_cmdset_0002: Change write buffer to 
> > > check correct value)
> > 
> > Can you put the Fixes tag on a single, and the format is
> > 
> > Fixes: <hash> ("message")
> > 
> > > Signed-off-by: Yi Huaijie <yihuaijie@...wei.com>
> > > Signed-off-by: Liu Jian <liujian56@...wei.com>
> > 
> > [1]http://patchwork.ozlabs.org/patch/1025566/
> > 
> > > ---
> > >  drivers/mtd/chips/cfi_cmdset_0002.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c 
> > > b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > index 72428b6..818e94b 100644
> > > --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > @@ -1876,14 +1876,14 @@ static int __xipram do_write_buffer(struct map_info *map, struct flchip *chip,
> > >  			continue;
> > >  		}
> > >  
> > > -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> > > -			break;
> > > -
> > >  		if (chip_good(map, adr, datum)) {
> > >  			xip_enable(map, chip, adr);
> > >  			goto op_done;
> > >  		}
> > >  
> > > +		if (time_after(jiffies, timeo))
> > > +			break;
> > > +
> > >  		/* Latency issues. Drop the lock, wait a while and retry */
> > >  		UDELAY(map, chip, adr, 1);
> > >  	}
> > 
> 
> BTW, the patch itself looks good to me. Ikegami, can you confirm it does the right thing?
> 
> Thanks,
> 
> Boris
> 

One comment to this patch. If value is written incorrectly quickly we will be
stuck in the loop even though nothing is going to change. For example a value was
written incorrectly after 1us, the loop was set to 1ms, function will return
after 1ms, this solution is not optimized for performance. I considered same
when working on this change and decided to do it different way.

Regards,
Przemek