[dm-devel] [PATCH] Re: dm-crypt: Fix error with too large bios

[Mikulas Patocka]

Yes, this should be backported. It was lost somehow.

Mike, please put it to your git.

Mikulas


On Wed, 10 Aug 2016, Eric Wheeler wrote:

> Hello Mikulas and dm-devel list,
> 
> The simple patch below with is confirmed to fix James Johnston's issue and 
> doesn't appear to be in v4.8-rc1:
> 
> This references the following patchwork entry:
>   https://patchwork.kernel.org/patch/9138595/
> 
> Can we get this pushed upstream for v4.8?
> 
> --
> Eric Wheeler
> 
> 
> On Fri, 27 May 2016, Mikulas Patocka wrote:
> > dm-crypt: Fix error with too large bios
> > 
> > When dm-crypt processes writes, it allocates a new bio in the function
> > crypt_alloc_buffer. The bio is allocated from a bio set and it can have at
> > most BIO_MAX_PAGES vector entries, however the incoming bio can be larger
> > if it was allocated by other means. For example, bcache creates bios
> > larger than BIO_MAX_PAGES. If the incoming bio is larger, bio_alloc_bioset
> > fails and error is returned.
> > 
> > To avoid the error, we test for too large bio in the function crypt_map
> > and dm_accept_partial_bio to split the bio. dm_accept_partial_bio trims
> > the current bio to the desired size and requests that the device mapper
> > core sends another bio with the rest of the data.
> > 
> > Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> > Cc: stable at vger.kernel.org	# v3.16+
> 
> Tested-by: James Johnston <johnstonj.public at codenest.com>
> 
> I tested this patch by:
> 
> 1.  Building v4.7-rc1 from Torvalds git repo.  Confirmed that original bug
>     still occurs on Ubuntu 15.10.
> 
> 2.  Applying your patch to v4.7-rc1.  My kill sequence no longer works,
>     and the writeback cache is now successfully flushed to disk, and the
>     cache can be detached from the backing device.
> 
> 3.  To check data integrity, copied 250 MB of /dev/urandom to some file
>     on main volume.  Then, dd copy this file to /dev/bcache0.  Then,
>     detached the cache device from the backing device.  Then, rebooted.
>     Then, dd copy /dev/bcache0 to another file on main volume.  Then,
>     diff the files and confirm no changes.
> 
> So it looks like it works, based on this admittedly brief testing.  Thanks!
> 
> Best regards,
> 
> James Johnston
> 
> 
> --
> dm-devel mailing list
> dm-devel at redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
> 
> Patch
> 
> Index: linux-4.6/drivers/md/dm-crypt.c
> ===================================================================
> --- linux-4.6.orig/drivers/md/dm-crypt.c
> +++ linux-4.6/drivers/md/dm-crypt.c
> @@ -2137,6 +2137,10 @@  static int crypt_map(struct dm_target *t
>  	struct dm_crypt_io *io;
>  	struct crypt_config *cc = ti->private;
>  
> +	if (unlikely(bio->bi_iter.bi_size > BIO_MAX_SIZE) &&
> +	    (bio->bi_rw & (REQ_FLUSH | REQ_DISCARD | REQ_WRITE)) == REQ_WRITE)
> +		dm_accept_partial_bio(bio, BIO_MAX_SIZE >> SECTOR_SHIFT);
> +
>  	/*
>  	 * If bio is REQ_FLUSH or REQ_DISCARD, just bypass crypt queues.
>  	 * - for REQ_FLUSH device-mapper core ensures that no IO is in-flight
> 
> 
> 
>