Re: [RFC][PATCH] firmware: Drop WARN from usermodehelper_read_trylock error case

From: Laura Abbott
Date: Wed Apr 29 2015 - 16:28:42 EST

On 04/28/2015 06:37 PM, Marcel Holtmann wrote:
Hi Laura,

We've received a number of reports of warnings when coming
out of suspend with certain bluetooth firmware configurations:

WARNING: CPU: 3 PID: 3280 at drivers/base/firmware_class.c:1126
Modules linked in: ccm ip6t_rpfilter ip6t_REJECT nf_reject_ipv6
xt_conntrack ebtable_nat ebtable_broute bridge stp llc ebtable_filter
ebtables ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6
ip6table_mangle ip6table_security ip6table_raw ip6table_filter
ip6_tables iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4
nf_nat nf_conntrack iptable_mangle iptable_security iptable_raw
binfmt_misc bnep intel_rapl iosf_mbi arc4 x86_pkg_temp_thermal
snd_hda_codec_hdmi coretemp kvm_intel joydev snd_hda_codec_realtek
iwldvm snd_hda_codec_generic kvm iTCO_wdt mac80211 iTCO_vendor_support
snd_hda_intel snd_hda_controller snd_hda_codec crct10dif_pclmul
snd_hwdep crc32_pclmul snd_seq crc32c_intel ghash_clmulni_intel uvcvideo
snd_seq_device iwlwifi btusb videobuf2_vmalloc snd_pcm videobuf2_core
serio_raw bluetooth cfg80211 videobuf2_memops sdhci_pci v4l2_common
videodev thinkpad_acpi sdhci i2c_i801 lpc_ich mfd_core wacom mmc_core
media snd_timer tpm_tis hid_logitech_hidpp wmi tpm rfkill snd mei_me mei
shpchp soundcore nfsd auth_rpcgss nfs_acl lockd grace sunrpc i915
i2c_algo_bit drm_kms_helper e1000e drm hid_logitech_dj ptp pps_core
CPU: 3 PID: 3280 Comm: kworker/u17:0 Not tainted 3.19.3-200.fc21.x86_64
Hardware name: LENOVO 343522U/343522U, BIOS GCET96WW (2.56 ) 10/22/2013
Workqueue: hci0 hci_power_on [bluetooth]
0000000000000000 0000000089944328 ffff88040acffb78 ffffffff8176e215
0000000000000000 0000000000000000 ffff88040acffbb8 ffffffff8109bc1a
0000000000000000 ffff88040acffcd0 00000000fffffff5 ffff8804076bac40
Call Trace:
[<ffffffff8176e215>] dump_stack+0x45/0x57
[<ffffffff8109bc1a>] warn_slowpath_common+0x8a/0xc0
[<ffffffff8109bd4a>] warn_slowpath_null+0x1a/0x20
[<ffffffff814dbe78>] _request_firmware+0x558/0x810
[<ffffffff814dc165>] request_firmware+0x35/0x50
[<ffffffffa03a7886>] btusb_setup_bcm_patchram+0x86/0x590 [btusb]
[<ffffffff814d40e6>] ? rpm_idle+0xd6/0x230
[<ffffffffa04d4801>] hci_dev_do_open+0xe1/0xa90 [bluetooth]
[<ffffffff810c51dd>] ? ttwu_do_activate.constprop.90+0x5d/0x70
[<ffffffffa04d5980>] hci_power_on+0x40/0x200 [bluetooth]
[<ffffffff810b487c>] process_one_work+0x14c/0x3f0
[<ffffffff810b52f3>] worker_thread+0x53/0x470
[<ffffffff810b52a0>] ? rescuer_thread+0x300/0x300
[<ffffffff810ba548>] kthread+0xd8/0xf0
[<ffffffff810ba470>] ? kthread_create_on_node+0x1b0/0x1b0
[<ffffffff81774958>] ret_from_fork+0x58/0x90
[<ffffffff810ba470>] ? kthread_create_on_node+0x1b0/0x1b0

This occurs after every resume.

When resuming, the bluetooth driver needs to re-request the
firmware. This re-request is happening before usermodehelper
is fully enabled. If the firmware load succeeded previously, the
caching behavior of the firmware code typically negates the
need to call the usermodehelper code again and the request
succeeds. If the firmware was never loaded because it isn't
actually present in the file system, this results in a call
to usermodehelper and a failure warning every resume. Rather
than have a WARN clogging up the kernel messages each time,
just drop the warn. There is still a dev_err for debugging

Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
This might be papering over a real issue but I'm not
familiar enough with any of suspend/resume, bluetooth,
or firmware loading to identify an alternate fix.
The backtrace is from bcm patchram but the problem
isn't limited to that hardware. Intel also does a
request firmware and I was able to reproduce the
same backtrace on that driver by requesting non-existant
firmware file.

so here is the thing with Bluetooth firmware. Some of them
are RAM patches to fix the ROM modules. Others are full firmware
that are required to be downloaded first.

For ROM modules, the RAM patching procedure is optional. So we
will proceed even if no firmware is available. This means that
the kernel will never cache it (since it is not there in the
first place) and also on every resume we have the same issues.
So optional firmware is something that happens for Bluetooth USB
> dongles a lot.

In the driver we know which firmwares are optional and which are
> required. So we could tell the firmware class this if this would make
> things better and result in clearer errors and warnings. Is that
> something we want here?

The response on another reply was

"Yes, it is a driver problem, and loading firmware from filesystem
isn't safe during resume, and that is the purpose of the warning."

It isn't clear if this means request_firmware shouldn't be called
on resume at all or if request_firmware shouldn't be called unless
we can guarantee it won't make a call into the file system. I'd
be okay with adding another api (request_optional_firmware?) to
represent this if the firmware maintainers aren't against the
concept. If the firmware maintainers are against the concept,
it seems like the only solution is to rework the bluetooth drivers
to not request anything on resume.



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