memory leaks from xfs_rw_bdev()

[Qian Cai]

Booting today's linux-next starts to have several memory leaks. Looks like the
new xfs_rw_bdev() was introduced in the commit "xfs: use bios directly to read
and write the log recovery buffers".

https://patchwork.kernel.org/patch/10977673/

unreferenced object 0xffff888f595487c0 (size 184):
 comm "mount", pid 1473, jiffies 4294946340 (age 14914.220s)
 hex dump (first 32 bytes):
ÂÂÂÂ00 00 00 00 00 00 00 00 08 40 28 67 8f 88 ff ffÂÂ.........@(g....
ÂÂÂÂ00 18 00 00 40 c6 00 00 00 00 00 00 00 00 00 00ÂÂ....@...........
 backtrace:
ÂÂÂÂ[<0000000031fb6250>] kmem_cache_alloc+0x272/0x400
ÂÂÂÂ[<000000008ce62f00>] mempool_alloc_slab+0x2d/0x40
ÂÂÂÂ[<000000004eaa8110>] mempool_alloc+0x10a/0x29e
ÂÂÂÂ[<00000000906127bf>] bio_alloc_bioset+0x150/0x330
ÂÂÂÂ[<000000005d5cc981>] xfs_rw_bdev+0x72/0x300 [xfs]
ÂÂÂÂ[<00000000bbf739cd>] xlog_do_io+0xd8/0x1a0 [xfs]
ÂÂÂÂ[<000000003815ee16>] xlog_bread+0x28/0x70 [xfs]
ÂÂÂÂ[<00000000883dc328>] xlog_find_verify_cycle+0x180/0x2c0 [xfs]
ÂÂÂÂ[<00000000457d45f8>] xlog_find_head+0x27c/0x5a0 [xfs]
ÂÂÂÂ[<000000009956dd1f>] xlog_find_tail+0xdb/0x530 [xfs]
ÂÂÂÂ[<00000000c0cdfde4>] xlog_recover+0x8f/0x2a0 [xfs]
ÂÂÂÂ[<00000000f87803cd>] xfs_log_mount+0x247/0x3b0 [xfs]
ÂÂÂÂ[<00000000e3a05975>] xfs_mountfs+0x7bd/0xe30 [xfs]
ÂÂÂÂ[<00000000128f1a43>] xfs_fs_fill_super+0x6f0/0xaa0 [xfs]
ÂÂÂÂ[<000000000ead1e3b>] mount_bdev+0x1d9/0x220
ÂÂÂÂ[<00000000d48a9588>] xfs_fs_mount+0x15/0x20 [xfs]