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

[Vladimir Davydov]

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);
 	}
-- 
2.1.4