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Alan Stern 11e485d8f8 USB: hub: Don't record a connect-change event during reset-resume 
commit 8099f58f1e upstream.

Paul Zimmerman reports that his USB Bluetooth adapter sometimes
crashes following system resume, when it receives a
Get-Device-Descriptor request while it is busy doing something else.

Such a request was added by commit a4f55d8b8c ("usb: hub: Check
device descriptor before resusciation").  It gets sent when the hub
driver's work thread checks whether a connect-change event on an
enabled port really indicates a new device has been connected, as
opposed to an old device momentarily disconnecting and then
reconnecting (which can happen with xHCI host controllers, since they
automatically enable connected ports).

The same kind of thing occurs when a port's power session is lost
during system suspend.  When the system wakes up it sees a
connect-change event on the port, and if the child device's
persist_enabled flag was set then hub_activate() sets the device's
reset_resume flag as well as the port's bit in hub->change_bits.  The
reset-resume code then takes responsibility for checking that the same
device is still attached to the port, and it does this as part of the
device's resume pathway.  By the time the hub driver's work thread
starts up again, the device has already been fully reinitialized and
is busy doing its own thing.  There's no need for the work thread to
do the same check a second time, and in fact this unnecessary check is
what caused the problem that Paul observed.

Note that performing the unnecessary check is not actually a bug.
Devices are supposed to be able to send descriptors back to the host
even when they are busy doing something else.  The underlying cause of
Paul's problem lies in his Bluetooth adapter.  Nevertheless, we
shouldn't perform the same check twice in a row -- and as a nice side
benefit, removing the extra check allows the Bluetooth adapter to work
more reliably.

The work thread performs its check when it sees that the port's bit is
set in hub->change_bits.  In this situation that bit is interpreted as
though a connect-change event had occurred on the port _after_ the
reset-resume, which is not what actually happened.

One possible fix would be to make the reset-resume code clear the
port's bit in hub->change_bits.  But it seems simpler to just avoid
setting the bit during hub_activate() in the first place.  That's what
this patch does.

(Proving that the patch is correct when CONFIG_PM is disabled requires
a little thought.  In that setting hub_activate() will be called only
for initialization and resets, since there won't be any resumes or
reset-resumes.  During initialization and hub resets the hub doesn't
have any child devices, and so this code path never gets executed.)

Reported-and-tested-by: Paul Zimmerman <pauldzim@gmail.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://marc.info/?t=157949360700001&r=1&w=2
CC: David Heinzelmann <heinzelmann.david@gmail.com>
CC: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/Pine.LNX.4.44L0.2001311037460.1577-100000@iolanthe.rowland.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2020-02-28 17:23:32 +01:00
arch s390/pci: Recover handle in clp_set_pci_fn() 2020-02-24 08:38:51 +01:00
block block, bfq: do not plug I/O for bfq_queues with no proc refs 2020-02-24 08:38:09 +01:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto crypto: essiv - fix AEAD capitalization and preposition use in help text 2020-02-24 08:38:32 +01:00
Documentation fbdev: fix numbering of fbcon options 2020-02-24 08:38:21 +01:00
drivers USB: hub: Don't record a connect-change event during reset-resume 2020-02-28 17:23:32 +01:00
fs btrfs: handle logged extent failure properly 2020-02-28 17:23:29 +01:00
include USB: core: add endpoint-blacklist quirk 2020-02-28 17:23:31 +01:00
init Revert "um: Enable CONFIG_CONSTRUCTORS" 2020-02-01 09:33:00 +00:00
ipc ipc/msg.c: consolidate all xxxctl_down() functions 2020-02-11 04:36:39 -08:00
kernel tracing: Fix now invalid var_ref_vals assumption in trace action 2020-02-24 08:38:47 +01:00
lib lib/scatterlist.c: adjust indentation in __sg_alloc_table 2020-02-24 08:38:47 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm mm/mmu_gather: invalidate TLB correctly on batch allocation failure and flush 2020-02-11 04:37:14 -08:00
net sunrpc: Fix potential leaks in sunrpc_cache_unhash() 2020-02-24 08:38:40 +01:00
samples samples/bpf: Set -fno-stack-protector when building BPF programs 2020-02-24 08:38:15 +01:00
scripts bpf, btf: Always output invariant hit in pahole DWARF to BTF transform 2020-02-24 08:38:40 +01:00
security selinux: ensure we cleanup the internal AVC counters on error in avc_update() 2020-02-24 08:38:19 +01:00
sound ASoC: sun8i-codec: Fix setting DAI data format 2020-02-28 17:23:27 +01:00
tools tc-testing: add missing 'nsPlugin' to basic.json 2020-02-24 08:38:49 +01:00
usr gen_initramfs_list.sh: fix 'bad variable name' error 2020-01-04 00:00:48 +09:00
virt KVM: arm64: Treat emulated TVAL TimerValue as a signed 32-bit integer 2020-02-14 16:53:04 -05:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: dump missing namespaces into a single modules.nsdeps file 2019-11-11 20:10:01 +09:00
.mailmap MAINTAINERS: update my email address 2020-01-11 14:33:39 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Linux 5.4-rc4 2019-10-29 04:43:29 -06:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: correct entries for ISDN/mISDN section 2020-02-11 04:36:38 -08:00
Makefile Linux 5.5.6 2020-02-24 08:38:51 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.