linux-kernel - kmemleak report after 9082e87bfbf8 ("block: remove struct bio

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Date:	Mon, 6 Jun 2016 12:26:20 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Christoph Hellwig <hch@....de>
Cc:	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...com>
Subject: kmemleak report after 9082e87bfbf8 ("block: remove struct bio_batch")

Hi Christoph,

I tried enabling kmemleak on 4.7-rc2 on an x86 host (macbook pro running
Debian sid) and I get some kmemleak reports every few minutes coming
from the block layer. Reverting commit 9082e87bfbf8 ("block: remove
struct bio_batch") makes them go away:

unreferenced object 0xffff880077859c00 (size 256):
  comm "upowerd", pid 1185, jiffies 4295046823 (age 1874.852s)
  hex dump (first 32 bytes):
    80 39 08 00 00 ea ff ff 00 10 00 00 00 00 00 00  .9..............
    00 00 00 00 00 00 00 00 00 e4 21 49 02 88 ff ff  ..........!I....
  backtrace:
    [<ffffffff811d244e>] kmem_cache_alloc+0xfe/0x250
    [<ffffffff812dc8b7>] bvec_alloc+0x57/0xe0
    [<ffffffff812dcaaf>] bio_alloc_bioset+0x16f/0x240
    [<ffffffff812eca7f>] next_bio+0x1f/0x50
    [<ffffffff812ecf1a>] blkdev_issue_zeroout+0xea/0x1d0
    [<ffffffffc025b610>] ext4_issue_zeroout+0x40/0x50 [ext4]
    [<ffffffffc028c58d>] ext4_ext_map_blocks+0x144d/0x1bb0 [ext4]
    [<ffffffff811839f4>] release_pages+0x254/0x310
    [<ffffffff8118437a>] __pagevec_release+0x2a/0x40
    [<ffffffffc025b297>] mpage_prepare_extent_to_map+0x227/0x2c0 [ext4]
    [<ffffffffc025b793>] ext4_map_blocks+0x173/0x5d0 [ext4]
    [<ffffffffc025f1d0>] ext4_writepages+0x700/0xd40 [ext4]
    [<ffffffff8121312e>] legitimize_mnt+0xe/0x50
    [<ffffffff811d244e>] kmem_cache_alloc+0xfe/0x250
    [<ffffffff81173fd5>] __filemap_fdatawrite_range+0xc5/0x100
    [<ffffffff81174113>] filemap_write_and_wait_range+0x33/0x70

It's coming from various processes, not just upowerd. I haven't got the
chance to dig further but you may have a better idea.

Thanks.

-- 
Catalin