[4.2.y-ckt stable] Patch "mmc: block: Use the mmc host device index as the mmcblk device index" has been added to the 4.2.y-ckt tree

[Peter Hurley]

Hi Kamal,

On 04/25/2016 12:44 PM, Kamal Mostafa wrote:
> This is a note to let you know that I have just added a patch titled
> 
>     mmc: block: Use the mmc host device index as the mmcblk device index
> 
> to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
> which can be found at:
> 
>     http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-4.2.y-queue
> 
> This patch is scheduled to be released in version 4.2.8-ckt9.

The commit that triggers this stable fix was first avail on 4.5
so shouldn't be necessary for 4.2.y [unless commit 520bd7a8b415
("mmc: core: Optimize boot time by detecting cards simultaneously"
was backported?]

Regards,
Peter Hurley



> If you, or anyone else, feels it should not be added to this tree, please 
> reply to this email.
> 
> For more information about the 4.2.y-ckt tree, see
> https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
> 
> Thanks.
> -Kamal
> 
> ---8<------------------------------------------------------------
> 
> From 0be97d0b4a5695ebc2872064effcae0cd58e9baf Mon Sep 17 00:00:00 2001
> From: Ulf Hansson <ulf.hansson at linaro.org>
> Date: Wed, 6 Apr 2016 16:12:08 +0200
> Subject: mmc: block: Use the mmc host device index as the mmcblk device index
> 
> commit 9aaf3437aa72ed5370bf32c99580a3fa2c330e3d upstream.
> 
> Commit 520bd7a8b415 ("mmc: core: Optimize boot time by detecting cards
> simultaneously") causes regressions for some platforms.
> 
> These platforms relies on fixed mmcblk device indexes, instead of
> deploying the defacto standard with UUID/PARTUUID. In other words their
> rootfs needs to be available at hardcoded paths, like /dev/mmcblk0p2.
> 
> Such guarantees have never been made by the kernel, but clearly the above
> commit changes the behaviour. More precisely, because of that the order
> changes of how cards becomes detected, so do their corresponding mmcblk
> device indexes.
> 
> As the above commit significantly improves boot time for some platforms
> (magnitude of seconds), let's avoid reverting this change but instead
> restore the behaviour of how mmcblk device indexes becomes picked.
> 
> By using the same index for the mmcblk device as for the corresponding mmc
> host device, the probe order of mmc host devices decides the index we get
> for the mmcblk device.
> 
> For those platforms that suffers from a regression, one could expect that
> this updated behaviour should be sufficient to meet their expectations of
> "fixed" mmcblk device indexes.
> 
> Another side effect from this change, is that the same index is used for
> the mmc host device, the mmcblk device and the mmc block queue. That
> should clarify their relationship.
> 
> Reported-by: Peter Hurley <peter at hurleysoftware.com>
> Reported-by: Laszlo Fiat <laszlo.fiat at gmail.com>
> Cc: Linus Torvalds <torvalds at linux-foundation.org>
> Fixes: 520bd7a8b415 ("mmc: core: Optimize boot time by detecting cards
> simultaneously")
> Signed-off-by: Ulf Hansson <ulf.hansson at linaro.org>
> Signed-off-by: Kamal Mostafa <kamal at canonical.com>
> ---
>  drivers/mmc/card/block.c | 18 +-----------------
>  1 file changed, 1 insertion(+), 17 deletions(-)
> 
> diff --git a/drivers/mmc/card/block.c b/drivers/mmc/card/block.c
> index 88c4e08..449937e 100644
> --- a/drivers/mmc/card/block.c
> +++ b/drivers/mmc/card/block.c
> @@ -86,7 +86,6 @@ static int max_devices;
> 
>  /* TODO: Replace these with struct ida */
>  static DECLARE_BITMAP(dev_use, MAX_DEVICES);
> -static DECLARE_BITMAP(name_use, MAX_DEVICES);
> 
>  /*
>   * There is one mmc_blk_data per slot.
> @@ -105,7 +104,6 @@ struct mmc_blk_data {
>  	unsigned int	usage;
>  	unsigned int	read_only;
>  	unsigned int	part_type;
> -	unsigned int	name_idx;
>  	unsigned int	reset_done;
>  #define MMC_BLK_READ		BIT(0)
>  #define MMC_BLK_WRITE		BIT(1)
> @@ -2109,19 +2107,6 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>  		goto out;
>  	}
> 
> -	/*
> -	 * !subname implies we are creating main mmc_blk_data that will be
> -	 * associated with mmc_card with dev_set_drvdata. Due to device
> -	 * partitions, devidx will not coincide with a per-physical card
> -	 * index anymore so we keep track of a name index.
> -	 */
> -	if (!subname) {
> -		md->name_idx = find_first_zero_bit(name_use, max_devices);
> -		__set_bit(md->name_idx, name_use);
> -	} else
> -		md->name_idx = ((struct mmc_blk_data *)
> -				dev_to_disk(parent)->private_data)->name_idx;
> -
>  	md->area_type = area_type;
> 
>  	/*
> @@ -2170,7 +2155,7 @@ static struct mmc_blk_data *mmc_blk_alloc_req(struct mmc_card *card,
>  	 */
> 
>  	snprintf(md->disk->disk_name, sizeof(md->disk->disk_name),
> -		 "mmcblk%u%s", md->name_idx, subname ? subname : "");
> +		 "mmcblk%u%s", card->host->index, subname ? subname : "");
> 
>  	if (mmc_card_mmc(card))
>  		blk_queue_logical_block_size(md->queue.queue,
> @@ -2324,7 +2309,6 @@ static void mmc_blk_remove_parts(struct mmc_card *card,
>  	struct list_head *pos, *q;
>  	struct mmc_blk_data *part_md;
> 
> -	__clear_bit(md->name_idx, name_use);
>  	list_for_each_safe(pos, q, &md->part) {
>  		part_md = list_entry(pos, struct mmc_blk_data, part);
>  		list_del(pos);
> --
> 2.7.4
>