Re: [PATCH] block_dev: fix crash on chained bios with O_DIRECT

[Hannes Reinecke <hare@suse.com>]

On 3/20/19 9:45 AM, Johannes Thumshirn wrote:
> On 20/03/2019 09:12, Hannes Reinecke wrote:
>> __blkdev_direct_IO_simple() is allocating a bio on the stack.
>> When that bio needs to be split bio_chain_endio() invokes bio_put()
>> on this bio, causing the kernel to crash in mempool_free() as the
>> bio was never allocated from a mempool in the first place.
>> So call bio_get() before submitting to avoid this problem.
> 
> Hmm this sounds as if we're just papering over the real issue here,
> which is calling bio_free() for bios not allocated using bio_alloc_bioset().
> 
> How about the following untested patch:
> 
>  From 9c8434e5bf81595e97ea5647437d12bfce0e37b6 Mon Sep 17 00:00:00 2001
> From: Johannes Thumshirn <jthumshirn@suse.de>
> Date: Wed, 20 Mar 2019 09:40:18 +0100
> Subject: [PATCH] bio: Introduce BIO_ALLOCED flag and check it in bio_free
> 
> When we're submitting a bio from stack and this ends up being split, we
> call bio_put(). bio_put() will eventually call bio_free() if the reference
> count drops to 0. But freeing the bio is wrong, as it was never allocated
> out of the bio's mempool.
> 
> Flag each normally allocated bio as 'BIO_ALLOCATED' and skip freeing if the
> flag isn't set.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
> ---
>   block/bio.c               | 4 ++++
>   include/linux/blk_types.h | 1 +
>   2 files changed, 5 insertions(+)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 4db1008309ed..caa8bc076377 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -253,6 +253,9 @@ static void bio_free(struct bio *bio)
>   	struct bio_set *bs = bio->bi_pool;
>   	void *p;
> 
> +	if (!bio_flagged(bio, BIO_ALLOCED))
> +		return;
> +
>   	bio_uninit(bio);
> 
>   	if (bs) {
> @@ -521,6 +524,7 @@ struct bio *bio_alloc_bioset(gfp_t gfp_mask,
> unsigned int nr_iovecs,
>   		bvl = bio->bi_inline_vecs;
>   	}
> 
> +	bio_set_flag(bio, BIO_ALLOCED);
>   	bio->bi_pool = bs;
>   	bio->bi_max_vecs = nr_iovecs;
>   	bio->bi_io_vec = bvl;
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index d66bf5f32610..14b4f87a1eab 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -229,6 +229,7 @@ struct bio {
>   				 * of this bio. */
>   #define BIO_QUEUE_ENTERED 11	/* can use blk_queue_enter_live() */
>   #define BIO_TRACKED 12		/* set if bio goes through the rq_qos path */
> +#define BIO_ALLOCED 13		/* set if the bio was allocated by
> bio_alloc_bioset */
> 
>   /* See BVEC_POOL_OFFSET below before adding new flags */
> 
Yeah, should work, too.
But we should be calling bio_uninit() for all bios.

Will you be sending an updated patch?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		               zSeries & Storage
hare@suse.com			               +49 911 74053 688
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