linux-kernel - Re: [PATCH] fs: System memory leak when running HTX with T10 DIF enabled

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Date:   Wed, 28 Jun 2017 14:11:31 -0700
From:   Shaohua Li <shli@...nel.org>
To:     Jens Axboe <axboe@...com>
Cc:     Christoph Hellwig <hch@....de>,
        Keith Busch <keith.busch@...el.com>,
        wenxiong@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
        bjking@...ux.vnet.ibm.com
Subject: Re: [PATCH] fs: System memory leak when running HTX with T10 DIF
 enabled

On Wed, Jun 28, 2017 at 12:57:50PM -0600, Jens Axboe wrote:
> On 06/28/2017 12:52 PM, Christoph Hellwig wrote:
> > On Wed, Jun 28, 2017 at 12:44:00PM -0600, Jens Axboe wrote:
> >> On 06/28/2017 12:38 PM, Christoph Hellwig wrote:
> >>> On Wed, Jun 28, 2017 at 12:34:15PM -0600, Jens Axboe wrote:
> >>>> That's what I sent out.
> >>>
> >>> Where?  Didn't see that anywhere..
> >>
> >> Looks like you weren't CC'ed on the original thread. About an hour ago.
> >>
> >>>> Here it is again. We should get this into 4.12,
> >>>> so would be great with a review or two.
> >>>
> >>> Can we rename __bio_free to bio_uninit and add a comment to bio_init
> >>> that it must be paried with bio_uninit?
> >>
> >> Let's keep it small for 4.12. We can do a cleanup on top of this for
> >> 4.13.
> > 
> > The rename is two additional lines for the patch, it's not going to
> > make a difference..
> 
> Sure, why not...
> 
> >>> Except for that this looks fine, although there are a lot more callers
> >>> that should get this treatment..
> >>
> >> Should only be an issue for on-stack bio's, since we don't go through
> >> the put/free path. Did a quick grep, looks like this is one of 3. One
> >> is floppy, which probably neither has DIF or uses blk-throttle. Then
> >> there's one in dm-bufio, didn't look too closely at that. Last one is
> >> this one.
> > 
> > Well, it's really all callers but bio_alloc_bioset itself that
> > will need this handling, as only bios that come from bio_alloc_bioset
> > will be freed through bio_free.  Most of them probably don't
> > support DIF, but they'll also miss the bio_disassociate_task call
> > this way, and will leak I/O context and css references if block
> > cgroup support is enabled.
> 
> I guess local allocs too will be affected.
> 
> I'm baffled we've had this issue for so long, and nobody's seen it.
> I knew DIF was never used (basically), but blk-throttle must have some
> users at least.

I fixed the same issue in the blktrace patches. It did the free in bio_endio.

 
> 
> 
> diff --git a/block/bio.c b/block/bio.c
> index 888e7801c638..f877d5e6d17f 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -240,7 +240,7 @@ struct bio_vec *bvec_alloc(gfp_t gfp_mask, int nr, unsigned long *idx,
>  	return bvl;
>  }
>  
> -static void __bio_free(struct bio *bio)
> +void bio_uninit(struct bio *bio)
>  {
>  	bio_disassociate_task(bio);
>  
> @@ -253,7 +253,7 @@ static void bio_free(struct bio *bio)
>  	struct bio_set *bs = bio->bi_pool;
>  	void *p;
>  
> -	__bio_free(bio);
> +	bio_uninit(bio);
>  
>  	if (bs) {
>  		bvec_free(bs->bvec_pool, bio->bi_io_vec, BVEC_POOL_IDX(bio));
> @@ -271,6 +271,11 @@ static void bio_free(struct bio *bio)
>  	}
>  }
>  
> +/*
> + * Users of this function have their own bio allocation. Subsequently,
> + * they must remember to pair any call to bio_init() with bio_uninit()
> + * when IO has completed, or when the bio is released.
> + */
>  void bio_init(struct bio *bio, struct bio_vec *table,
>  	      unsigned short max_vecs)
>  {
> @@ -297,7 +302,7 @@ void bio_reset(struct bio *bio)
>  {
>  	unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS);
>  
> -	__bio_free(bio);
> +	bio_uninit(bio);
>  
>  	memset(bio, 0, BIO_RESET_BYTES);
>  	bio->bi_flags = flags;
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 519599dddd36..0a7404ef9335 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -263,7 +263,10 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
>  		kfree(vecs);
>  
>  	if (unlikely(bio.bi_error))
> -		return bio.bi_error;
> +		ret = bio.bi_error;
> +
> +	bio_uninit(&bio);
> +
>  	return ret;
>  }
>  
> diff --git a/include/linux/bio.h b/include/linux/bio.h
> index d1b04b0e99cf..a7e29fa0981f 100644
> --- a/include/linux/bio.h
> +++ b/include/linux/bio.h
> @@ -426,6 +426,7 @@ extern void bio_advance(struct bio *, unsigned);
>  
>  extern void bio_init(struct bio *bio, struct bio_vec *table,
>  		     unsigned short max_vecs);
> +extern void bio_uninit(struct bio *);
>  extern void bio_reset(struct bio *);
>  void bio_chain(struct bio *, struct bio *);
>  
> 
> -- 
> Jens Axboe
>