Re: [BUG] NULL pointer in raid1_make_request passed to bio_trim when adding md as bcache caching dev

[Shaohua Li <shli@kernel.org>]

On Sat, Mar 26, 2016 at 05:46:16PM +0100, Sebastian Roesner wrote:
> Hello Ming, Eric,
> 
> Am 26.03.2016 um 16:40 schrieb Ming Lei:
> > From the trace, looks the bio returned from bio_clone_mddev() is NULL,
> >and maybe the source bio is buggy, something like the attached patch
> >might be helpful, could you apply the attached debug patch, reproduce
> >and post the log?
> 
> I was able to reproduce it on a non-productive system, but only after
> copying the bcache superblocks/partition starts from the original system,
> with new created ones it worked fine.
> 
> Full trace and check_bio output can be found here:
> 
> http://pastebin.com/ngvGGHBZ

320 bvecs exceeds what bio-clone_set can handle. Could you please try below patch?

commit 92761dad7ff6e1bf25de247e0064dd398e797599
Author: Shaohua Li <shli@fb.com>
Date:   Mon Mar 28 10:54:35 2016 -0700

    block: don't make BLK_DEF_MAX_SECTORS too big
    
    bio_alloc_bioset() allocates bvecs from bvec_slabs which can only allocate
    maximum 256 bvec (eg, 1M for 4k pages). We can't bump BLK_DEF_MAX_SECTORS to
    exceed this value otherwise bio_alloc_bioset will fail.
    
    This fixes commit 30e2bc08b2bb7c069. We probably should make the bvec_slabs
    hold bigger bvecs if bigger bio size is required.
    
    Signed-off-by: Shaohua Li <shli@fb.com>

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 7e5d7e0..da64325 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1153,7 +1153,11 @@ extern int blk_verify_command(unsigned char *cmd, fmode_t has_write_perm);
 enum blk_default_limits {
 	BLK_MAX_SEGMENTS	= 128,
 	BLK_SAFE_MAX_SECTORS	= 255,
-	BLK_DEF_MAX_SECTORS	= 2560,
+	/*
+	 * if you change this, please also change bvec_alloc and BIO_MAX_PAGES.
+	 * Otherwise bio_alloc_bioset will break.
+	 */
+	BLK_DEF_MAX_SECTORS	= BIO_MAX_SECTORS,
 	BLK_MAX_SEGMENT_SIZE	= 65536,
 	BLK_SEG_BOUNDARY_MASK	= 0xFFFFFFFFUL,
 };