Re: [PATCH] mtd: fix calculating partition end address

From: Miquel Raynal <miquel.raynal@bootlin.com>
To: "Rafał Miłecki" <rafal@milecki.pl>
Cc: "Richard Weinberger" <richard@nod.at>,
	"Rafał Miłecki" <zajec5@gmail.com>,
	linux-mtd@lists.infradead.org,
	"Vignesh Raghavendra" <vigneshr@ti.com>,
	"Boris Brezillon" <bbrezillon@kernel.org>
Subject: Re: [PATCH] mtd: fix calculating partition end address
Date: Sat, 2 May 2020 20:04:01 +0200	[thread overview]
Message-ID: <20200502200401.7dfa5def@xps13> (raw)
In-Reply-To: <20200309162223.15582d12@xps13>

Hi Rafal,

Miquel Raynal <miquel.raynal@bootlin.com> wrote on Mon, 9 Mar 2020
16:22:23 +0100:

> Hi Rafał,
> 
> Rafał Miłecki <rafal@milecki.pl> wrote on Mon, 9 Mar 2020 16:08:12
> +0100:
> 
> > On 09.03.2020 15:22, Miquel Raynal wrote:  
> > > Rafał Miłecki <rafal@milecki.pl> wrote on Mon, 09 Mar 2020 15:19:10
> > > +0100:
> > >     
> > >> On 2020-03-09 15:04, Miquel Raynal wrote:    
> > >>> Rafał Miłecki <zajec5@gmail.com> wrote on Mon,  9 Mar 2020 08:44:45
> > >>> +0100:    
> > >>>    >>>> From: Rafał Miłecki <rafal@milecki.pl>    
> > >>>>>> This fixes check for partitions that don't start at beginning of their    
> > >>>> parents. Missing partition's offset in formula could result in forcing
> > >>>> read-only incorrectly.    
> > >>>>>> Fixes: 6750f61a13a0 ("mtd: improve calculating partition boundaries >> when checking for alignment")    
> > >>>> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
> > >>>> ---
> > >>>>   drivers/mtd/mtdpart.c | 2 +-
> > >>>>   1 file changed, 1 insertion(+), 1 deletion(-)    
> > >>>>>> diff --git a/drivers/mtd/mtdpart.c b/drivers/mtd/mtdpart.c    
> > >>>> index 7328c066c5ba..c683b432cc5e 100644
> > >>>> --- a/drivers/mtd/mtdpart.c
> > >>>> +++ b/drivers/mtd/mtdpart.c
> > >>>> @@ -524,7 +524,7 @@ static struct mtd_part *allocate_partition(struct >> mtd_info *parent,
> > >>>>   			part->name);
> > >>>>   	}    
> > >>>>>> -	tmp = part_absolute_offset(parent) + slave->mtd.size;    
> > >>>> +	tmp = part_absolute_offset(parent) + slave->offset + >> slave->mtd.size;    
> > >>>
> > >>> I think you are doing the change at the wrong place, if you want to
> > >>> check where the partition *starts* you should do it a few lines above.
> > >>> But I think the check should be here as well, probably.    
> > >>
> > >> The check where the partition *starts* is OK and I don't mean to change
> > >> it. The bug is about calculating absolute *end* address of partition.    
> > > 
> > > Can you detail a little bit then? Because I don't see the issue anymore
> > > even though I am convinced something is wrong here :)    
> > 
> > Please consider following partitions layout:
> > * bcm47xxsflash
> > ├─ boot		0x000000000000-0x000000040000
> > └┬ firmware	0x000000040000-0x000001000000
> >   ├─ linux	0x00000000001c-0x00000018f800
> >   └┬ container	0x00000018f800-0x000000fc0000
> >    ├─ foo	0x000000000000-0x000000630800
> >    └─ bar	0x000000630800-0x000000e30800 (size: 0x800000)
> > 
> > 
> > Existing (correct) *start* calculation:
> > bar start: 0 + 0x040000 + 0x18f800 + 0x630800 = 0x800000
> > 
> > Existing (wrong) end calculation:
> > bar end: 0 + 0x040000 + 0x18f800 + 0x800000 = 0x9cf800
> > 
> > Fixed (correct) end calculation:
> > bar end: 0 + 0x040000 + 0x18f800 + 0x630800 + 0x800000 = 0x1000000  
> 
> Ok I get it! I think mentioning "partitions that don't start at
> beginning of their parents", despite being true, was misleading to me
> as I understood "leaving extra space with the start of their parent".
> 
> I suppose you also have the issue with "container" too?
> 
> Anyway, I think the fix is fine. A better formulation for the commit
> log would be welcome :) (maybe adding this example is a good idea!)

I don't remember having applied this fix yet, would you mind resending
this patch with an enhanced commit log (your example was a good one I
think).

Thanks,
 Miquèl

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