linux-kernel - Re: [RFC][PATCH] module: Limit line length of module prints

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Message-ID: <56709891.8040203@redhat.com>
Date:	Tue, 15 Dec 2015 14:47:45 -0800
From:	Laura Abbott <labbott@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Laura Abbott <labbott@...oraproject.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] module: Limit line length of module prints

On 12/13/2015 05:06 PM, Rusty Russell wrote:
> Laura Abbott <labbott@...hat.com> writes:
>> On 12/11/2015 01:39 AM, Rusty Russell wrote:
>>> Laura Abbott <labbott@...oraproject.org> writes:
>>>> print_modules currently uses pr_cont to print all module information.
>>>> This has the side effect of printing lots of modules on one very long
>>>> line. This makes copy/pasting oopses more effort if manual wrapping is
>>>> required. Place a reasonable limit (80 chars) on the number of modules
>>>> on each line.
>>>>
>>>> Signed-off-by: Laura Abbott <labbott@...oraproject.org>
>>>> ---
>>>> Does this bother anyone else or am I the only one who hates dealing
>>>> with the long lines of "Modules linked in"?
>>>
>>> Never bothered me, but I'm a bit odd :)  I worry more about the effect
>>> on machine parsing.
>>>
>>
>> Yes, that was a concern I had as well, but the module list seems to get
>> wrapped eventually (although at a much longer length) so it seems like
>> if machine parsing can handle one wrap it can handle multiple wraps.
>
> Does it?  I find that code very hard to parse, but seems like something
> happens at 1024 chars.
>
> But my testing here doesn't show any such break in dmesg, nor on serial
> console.
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 912e891e0e2f..f882d9d99844 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -3925,6 +3925,12 @@ static const struct file_operations proc_modules_operations = {
>
>   static int __init proc_modules_init(void)
>   {
> +	int x;
> +	printk("Test of long line:");
> +	for (x = 0; x < 1024; x++)
> +		pr_cont("%c%c", (x % 26) + 'A', (x % 26) + 'A');
> +	pr_cont("\n");
> +			
>   	proc_create("modules", 0, NULL, &proc_modules_operations);
>   	return 0;
>   }
>
> Confused,
> Rusty.
>

So this is what I see from an example warning:

[   51.432399] ------------[ cut here ]------------
[   51.432406] WARNING: CPU: 2 PID: 77 at block/genhd.c:626 add_disk+0x480/0x4e0()
[   51.432407] Modules linked in: uas usb_storage scsi_dh_alua rfcomm
fuse cmac ccm xt_CHECKSUM ipt_MASQUERADE nf_nat_masquerade_ipv4 tun
nf_conntrack_netbios_ns nf_conntrack_broadcast ip6t_rpfilter
ip6t_REJECT nf_reject_ipv6 xt_conntrack ebtable_filter ebtable_nat
ebtable_broute bridge stp llc ebtables ip6table_mangle ip6table_nat
nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_raw
ip6table_security ip6table_filter ip6_tables iptable_mangle iptable_nat
nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack
iptable_raw iptable_security bnep intel_rapl iTCO_wdt
iTCO_vendor_support iosf_mbi x86_pkg_temp_thermal coretemp kvm_intel
kvm irqbypass crct10dif_pclmul crc32_pclmul crc32c_intel arc4 uvcvideo
iwlmvm videobuf2_vmalloc videobuf2_v4l2 btusb videobuf2_core mac80211
btrtl videobuf2_memops
[   51.432460]  v4l2_common joydev btbcm videodev btintel iwlwifi
snd_hda_codec_realtek media bluetooth cfg80211 snd_hda_codec_generic
snd_hda_codec_hdmi lpc_ich intel_pch_thermal i2c_i801 shpchp
snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep wmi snd_seq
thinkpad_acpi snd_seq_device rfkill snd_pcm mei_me snd_timer snd
soundcore mei tpm_tis tpm nfsd auth_rpcgss nfs_acl lockd grace sunrpc
i915 i2c_algo_bit drm_kms_helper serio_raw e1000e drm ptp pps_core
video fjes
[   51.432501] CPU: 2 PID: 77 Comm: kworker/u16:1 Tainted: G        W       4.4.0-0.rc4.git2.1.fc24.x86_64 #1
[   51.432503] Hardware name: LENOVO 20BTS1N700/20BTS1N700, BIOS N14ET28W (1.06 ) 03/12/2015
[   51.432507] Workqueue: events_unbound async_run_entry_fn
[   51.432509]  0000000000000000 000000002902d154 ffff88021f893c38 ffffffff81427dc9
[   51.432513]  0000000000000000 ffff88021f893c70 ffffffff810add82 ffff880203baa000
[   51.432517]  ffff880203baa0b0 ffff880203baa00c ffff880215028000 ffff880036108600
[   51.432520] Call Trace:
[   51.432525]  [<ffffffff81427dc9>] dump_stack+0x4b/0x72
[   51.432529]  [<ffffffff810add82>] warn_slowpath_common+0x82/0xc0
[   51.432531]  [<ffffffff810adeca>] warn_slowpath_null+0x1a/0x20
[   51.432534]  [<ffffffff814088f0>] add_disk+0x480/0x4e0
[   51.432538]  [<ffffffff815d3d55>] sd_probe_async+0x115/0x1d0
[   51.432541]  [<ffffffff810d717a>] async_run_entry_fn+0x4a/0x140
[   51.432544]  [<ffffffff810cc160>] process_one_work+0x230/0x6a0
[   51.432546]  [<ffffffff810cc0c9>] ? process_one_work+0x199/0x6a0
[   51.432549]  [<ffffffff810cc61e>] worker_thread+0x4e/0x450
[   51.432552]  [<ffffffff810cc5d0>] ? process_one_work+0x6a0/0x6a0
[   51.432554]  [<ffffffff810d35b1>] kthread+0x101/0x120
[   51.432558]  [<ffffffff81108c89>] ? trace_hardirqs_on_caller+0x129/0x1b0
[   51.432560]  [<ffffffff810d34b0>] ? kthread_create_on_node+0x250/0x250
[   51.432564]  [<ffffffff8187875f>] ret_from_fork+0x3f/0x70
[   51.432566]  [<ffffffff810d34b0>] ? kthread_create_on_node+0x250/0x250
[   51.432568] ---[ end trace ea38cc3cfd710baf ]---

The modules are split over two lines judging by the time stamps but I'm
not sure why. I don't see it when using pr_cont in the example.

Thanks,
Laura
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