From: Vinson Lee <vlee@twopensource.com>
Subject: ext4_da_update_reserve_space warning with kernel 3.10
Date: Thu, 18 Dec 2014 17:23:22 -0800
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Cc: linux-ext4@vger.kernel.org
To: "Theodore Ts'o" <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Jan Kara <jack@suse.cz>
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Hi.

We're triggering a kernel warning in ext4_da_update_reserve_space on
kernels 3.4 and 3.10. We do not have a reproducible test case, but the
warning happens more frequently with a slow network.

EXT4-fs warning (device sdh1): ext4_da_update_reserve_space:362: ino
1310732, allocated 1 with only 0 reserved metadata blocks (releasing 1
blocks with reserved 14 data blocks)
------------[ cut here ]------------
WARNING: at fs/ext4/inode.c:363 ext4_da_update_reserve_space+0xe7/0x20c()
Modules linked in: netconsole configfs ipv6 ppdev parport_pc lp
parport tcp_diag inet_diag ipmi_si ipmi_devintf ipm
O_wdt iTCO_vendor_support acpi_cpufreq freq_table mperf coretemp
kvm_intel kvm crc32c_intel ghash_clmulni_intel mic
i2c_core lpc_ich mfd_core shpchp mlx4_en mlx4_core video mpt2sas
scsi_transport_sas raid_class
CPU: 0 PID: 50134 Comm: java Not tainted 3.10.50 #1
 0000000000000000 ffff880595dc1bb0 ffffffff814a4094 ffff880595dc1be8
 ffffffff8103cbf9 0000000000000000 ffff88039cdd1ef0 000000000000000e
 ffff880052527f60 ffff8807e9ad6000 ffff880595dc1bf8 ffffffff8103ccbf
Call Trace:
 [<ffffffff814a4094>] dump_stack+0x19/0x1b
 [<ffffffff8103cbf9>] warn_slowpath_common+0x65/0x7d
 [<ffffffff8103ccbf>] warn_slowpath_null+0x1a/0x1c
 [<ffffffff81190b7e>] ext4_da_update_reserve_space+0xe7/0x20c
 [<ffffffff811b30e7>] ext4_ext_map_blocks+0xae5/0xc09
 [<ffffffff81190ed5>] ext4_map_blocks+0x232/0x3a0
 [<ffffffff81192e28>] mpage_da_map_and_submit+0x8e/0x32c
 [<ffffffff8119375e>] ext4_da_writepages+0x2cf/0x483
 [<ffffffff810ed6d3>] do_writepages+0x1e/0x2c
 [<ffffffff810e5b3e>] __filemap_fdatawrite_range+0x55/0x57
 [<ffffffff810e7ef7>] SyS_fadvise64_64+0x163/0x1da
 [<ffffffff810e7f7c>] SyS_fadvise64+0xe/0x12
 [<ffffffff814aee46>] system_call_fastpath+0x1a/0x1f
---[ end trace bfdca050e80bbf21 ]---


This looks similar to a bug fixed by 3.12 commit "ext4: fix warning in
ext4_da_update_reserve_space()" [1]. However, this commit wasn't
backported to stable [2].

Cheers,
Vinson

[1] https://bugzilla.kernel.org/show_bug.cgi?id=63511
[2] http://lists.openwall.net/linux-ext4/2013/10/23/7