Re: ext4_da_update_reserve_space warning with kernel 3.10

[Theodore Ts'o <tytso@mit.edu>]

On Thu, Dec 18, 2014 at 05:23:22PM -0800, Vinson Lee wrote:
> 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)

Known problem, and fixed in newer kernels.  In fact, the warning is
harmless with the 3.10 kernels (since it includes commit 27dd4385422)
which prevents us from failing to be able to allocate metadata blocks.
In later kernels, as suggested by the commit description, we
eliminated this particular warning since it was no longer necessary.
As far as the 3.4 kernel is concerned, you could try backporting
27dd4385422, although there's a good chance enough stuff has changed
that the backport might not be at all trivial.

Regards,

					- Ted


> ------------[ 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