mtdblock read sector and cache_data == NULL

mtdblock read sector and cache_data == NULL

[Cestonaro Thilo]

Hey,

I think the cache_data buffer is used uninitialized in case no write
prepends the first read.

Initialization of cache_data buffer:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/mtd/mtdblock.c?id=refs/tags/v3.14-rc2#n300
--------------------

    if (!(mbd->mtd->flags & MTD_NO_ERASE) && mbd->mtd->erasesize) {
        mtdblk->cache_size = mbd->mtd->erasesize;
        mtdblk->cache_data = NULL;
    }
----------------

And later in do_cached_read it is just used with mtdblock->cache_data +
offset.
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/mtd/mtdblock.c?id=refs/tags/v3.14-rc2#n243

The only allocation I can find is in writesector function, so I figured
that the mtd_read will get NULL+offset in the first read.
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/mtd/mtdblock.c?id=refs/tags/v3.14-rc2#n272

Is it correct to place the same if unlikely stuff in the
mtdblock_readsect function like in the mtdblock_writesect one?

Greetings
Thilo

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Re: mtdblock read sector and cache_data == NULL

[Cestonaro Thilo]

hey,

forget it :) ... I got confused ....

Greetings Thilo

On 11.02.2014 09:36, Cestonaro Thilo wrote:
> Hey,
>
> I think the cache_data buffer is used uninitialized in case no write
> prepends the first read.
>
> Initialization of cache_data buffer:
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/mtd/mtdblock.c?id=refs/tags/v3.14-rc2#n300
> --------------------
>
>     if (!(mbd->mtd->flags & MTD_NO_ERASE) && mbd->mtd->erasesize) {
>         mtdblk->cache_size = mbd->mtd->erasesize;
>         mtdblk->cache_data = NULL;
>     }
> ----------------
>
> And later in do_cached_read it is just used with mtdblock->cache_data +
> offset.
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/mtd/mtdblock.c?id=refs/tags/v3.14-rc2#n243
>
> The only allocation I can find is in writesector function, so I figured
> that the mtd_read will get NULL+offset in the first read.
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/mtd/mtdblock.c?id=refs/tags/v3.14-rc2#n272
>
> Is it correct to place the same if unlikely stuff in the
> mtdblock_readsect function like in the mtdblock_writesect one?
>
> Greetings
> Thilo
>


-- 
With best regards
Thilo Cestonaro

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