[Devel] [PATCH rh7] ploop: use GFP_NOIO in ploop_make_request

[Konstantin Khorenko]

Maxim, please review.

Do we need the same in PCS6?

--
Best regards,

Konstantin Khorenko,
Virtuozzo Linux Kernel Team

On 08/17/2015 04:30 PM, Vladimir Davydov wrote:
> Currently, we use GFP_NOFS, which may result in a dead lock as follows:
>
> filemap_fault
>   do_mpage_readpage
>    submit_bio
>     generic_make_request                 initializes current->bio_list
>                                          calls make_request_fn
>      ploop_make_request
>       bio_alloc(GFP_NOFS)
>        kmem_cache_alloc
>         memcg_charge_kmem
>          try_to_free_mem_cgroup_pages
>           swap_writepage
>            generic_make_request          puts bio on current->bio_list
>          try_to-free_mem_cgroup_pages
>           wait_on_page_writeback
>
> The wait_on_page_writeback will never complete then, because the
> corresponding bio is on current->bio_list and for it to get to the queue
> we must return from ploop_make_request first.
>
> The stack trace of a hung task:
>
> [<ffffffff8115ae2e>] sleep_on_page+0xe/0x20
> [<ffffffff8115abb6>] wait_on_page_bit+0x86/0xb0
> [<ffffffff8116f4b2>] shrink_page_list+0x6e2/0xaf0
> [<ffffffff8116ff2b>] shrink_inactive_list+0x1cb/0x610
> [<ffffffff81170ab5>] shrink_lruvec+0x395/0x790
> [<ffffffff81171031>] shrink_zone+0x181/0x350
> [<ffffffff811715a0>] do_try_to_free_pages+0x170/0x530
> [<ffffffff81171b76>] try_to_free_mem_cgroup_pages+0xb6/0x140
> [<ffffffff811c6b5e>] __mem_cgroup_try_charge+0x1de/0xd70
> [<ffffffff811c8c4b>] memcg_charge_kmem+0x9b/0x100
> [<ffffffff811c8e1b>] __memcg_charge_slab+0x3b/0x90
> [<ffffffff811b3664>] new_slab+0x264/0x3f0
> [<ffffffff815e97c6>] __slab_alloc+0x315/0x48f
> [<ffffffff811b49ac>] kmem_cache_alloc+0x1cc/0x210
> [<ffffffff8115e4b5>] mempool_alloc_slab+0x15/0x20
> [<ffffffff8115e5f9>] mempool_alloc+0x69/0x170
> [<ffffffff8120bd42>] bvec_alloc+0x92/0x120
> [<ffffffff8120bfb8>] bio_alloc_bioset+0x1e8/0x2e0
> [<ffffffffa0072246>] ploop_make_request+0x2a6/0xac0 [ploop]
> [<ffffffff81297172>] generic_make_request+0xe2/0x130
> [<ffffffff81297237>] submit_bio+0x77/0x1c0
> [<ffffffff8121341f>] do_mpage_readpage+0x37f/0x6e0
> [<ffffffff8121386b>] mpage_readpages+0xeb/0x160
> [<ffffffffa01a051c>] ext4_readpages+0x3c/0x40 [ext4]
> [<ffffffff811683c0>] __do_page_cache_readahead+0x1e0/0x260
> [<ffffffff81168b11>] ra_submit+0x21/0x30
> [<ffffffff8115dea1>] filemap_fault+0x321/0x4b0
> [<ffffffff811864ca>] __do_fault+0x8a/0x560
> [<ffffffff8118b2d0>] handle_mm_fault+0x3d0/0xd80
> [<ffffffff815f73ee>] __do_page_fault+0x15e/0x530
> [<ffffffff815f77da>] do_page_fault+0x1a/0x70
> [<ffffffff815f3a08>] page_fault+0x28/0x30
>
> https://jira.sw.ru/browse/PSBM-38842
>
> Signed-off-by: Vladimir Davydov <vdavydov at parallels.com>
> ---
>   drivers/block/ploop/dev.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/block/ploop/dev.c b/drivers/block/ploop/dev.c
> index 30eb8a7551e5..f37df4dacf8c 100644
> --- a/drivers/block/ploop/dev.c
> +++ b/drivers/block/ploop/dev.c
> @@ -717,7 +717,7 @@ preallocate_bio(struct bio * orig_bio, struct ploop_device * plo)
>   	}
>
>   	if (nbio == NULL)
> -		nbio = bio_alloc(GFP_NOFS, max(orig_bio->bi_max_vecs, block_vecs(plo)));
> +		nbio = bio_alloc(GFP_NOIO, max(orig_bio->bi_max_vecs, block_vecs(plo)));
>   	return nbio;
>   }
>
> @@ -852,7 +852,7 @@ static void ploop_make_request(struct request_queue *q, struct bio *bio)
>
>   	if (!current->io_context) {
>   		struct io_context *ioc;
> -		ioc = get_task_io_context(current, GFP_NOFS, NUMA_NO_NODE);
> +		ioc = get_task_io_context(current, GFP_NOIO, NUMA_NO_NODE);
>   		if (ioc)
>   			put_io_context(ioc);
>   	}
>