Re: [PATCH] mtd: Add locking to cfi_cmdset_001:do_getlockstatus_oneblock

[Joakim Tjernlund <joakim.tjernlund@transmode.se>]

On Fri, 2015-11-06 at 14:49 +0100, Mark Marshall wrote:
> The function (do_getlockstatus_oneblock) switches the flash out of
> array-read mode and into query mode.  It should not run in parallel to
> another function that uses array-read mode.  We therefore need to
> acquire the chip mutex and call get_chip(..., FL_JEDEC_QUERY).
> 
> I also assume that we should invalidate the cache in the same way that
> we do for do_otp_read.
> 
> Signed-off-by: Mark Marshall <Mark.Marshall@omicron.at>
> ---
> 
> Hi all,
> 
> We have had a device in production (and operation) for a long time
> running Linux and using a CFI NOR flash chip.  We have recently
> started to get devices come back from the field with strange errors in
> the JFFS2 file system that is on this flash.  It appeared that blocks
> of files on the image were being dropped (not flash blocks, just 4K
> sections from the middle of the files were being replaced with 0's).
> 
> After some debugging I found that sometimes, when the JFFS2 FS was
> reading the JFFS2 inode block it would get an CRC error.  After adding
> some debug code I could see that in the error cases the "second half"
> of the read data was replaced with a fixed repeating pattern, and that
> this pattern was part of the CFI "QRY" data (It contained the flash
> manufacturer and device ID's).
> 
> This led me to think that maybe the problem was that some part of the
> MTD code was switching the device out of the normal "array-read" mode
> and into the query mode.  After looking through the mtd code I found
> that the function 'do_getlockstatus_oneblock' does switch the mode of
> the flash without taking the chip mutex.  Adding code to take the
> mutex has fixed our problem.
> 
> I am slightly surprised that no one else has seen this bug - the only
> thing I can think of is that reading the lock status of the flash is
> not something that happens in normal operation very often?  We have a
> process on the device that generates a hardware check report at boot
> up, and one of the things that it does is report on the 'locked'
> status of the flash.  This is always running while the JFFS2 code is
> performing it's initial scan.

We have! Been looking at it for a while now, thinking it is an bug
in erase suspend for small blocks. We even contacted Micron for confirmation.
Even got at few patches to address som other issues we found during troubleshooting this.

I will test your patch 

> 
> The bug is fairly easy to reproduce if you have a system with the
> correct type of flash.  In one terminal run something like:
> 
>  while true ; do ( hd -n 65536 /dev/mtd0 | md5sum ) ; done
> 
> And in a second terminal run a program or utility that will check the
> lock status of the flash (mtdinfo should work).  Assuming nothing else
> is writing to the flash partition mtd0 the md5sum will remain
> constant.  When the bug bites you can see the md5sum change (but then
> recover).
> 
> Best Regards,
> 
> Mark Marshall
> 
>  drivers/mtd/chips/cfi_cmdset_0001.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/mtd/chips/cfi_cmdset_0001.c
> b/drivers/mtd/chips/cfi_cmdset_0001.c
> index 286b97a..d675efb 100644
> --- a/drivers/mtd/chips/cfi_cmdset_0001.c
> +++ b/drivers/mtd/chips/cfi_cmdset_0001.c
> @@ -2051,13 +2051,32 @@ static int __xipram
> do_getlockstatus_oneblock(struct map_info *map,
>  {
>  	struct cfi_private *cfi = map->fldrv_priv;
>  	int status, ofs_factor = cfi->interleave * cfi->device_type;
> +	int ret;
> 
>  	adr += chip->start;
> +
> +	mutex_lock(&chip->mutex);
> +	ret = get_chip(map, chip, adr, FL_JEDEC_QUERY);
> +	if (ret) {
> +		mutex_unlock(&chip->mutex);
> +		return ret;
> +	}
> +
> +	/* let's ensure we're not reading back cached data from array mode */
> +	INVALIDATE_CACHED_RANGE(map, adr+(2*ofs_factor), 1);
> +
>  	xip_disable(map, chip, adr+(2*ofs_factor));
>  	map_write(map, CMD(0x90), adr+(2*ofs_factor));
>  	chip->state = FL_JEDEC_QUERY;
>  	status = cfi_read_query(map, adr+(2*ofs_factor));
>  	xip_enable(map, chip, 0);
> +
> +	/* then ensure we don't keep query data in the cache */
> +	INVALIDATE_CACHED_RANGE(map, adr+(2*ofs_factor), 1);
> +
> +	put_chip(map, chip, adr);
> +	mutex_unlock(&chip->mutex);
> +
>  	return status;
>  }
>