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Alvin Šipraga 3bc7324e49 usb: gadget: u_audio: don't let userspace block driver unbind 
commit 6c67ed9ad9 upstream.

In the unbind callback for f_uac1 and f_uac2, a call to snd_card_free()
via g_audio_cleanup() will disconnect the card and then wait for all
resources to be released, which happens when the refcount falls to zero.
Since userspace can keep the refcount incremented by not closing the
relevant file descriptor, the call to unbind may block indefinitely.
This can cause a deadlock during reboot, as evidenced by the following
blocked task observed on my machine:

  task:reboot  state:D stack:0   pid:2827  ppid:569    flags:0x0000000c
  Call trace:
   __switch_to+0xc8/0x140
   __schedule+0x2f0/0x7c0
   schedule+0x60/0xd0
   schedule_timeout+0x180/0x1d4
   wait_for_completion+0x78/0x180
   snd_card_free+0x90/0xa0
   g_audio_cleanup+0x2c/0x64
   afunc_unbind+0x28/0x60
   ...
   kernel_restart+0x4c/0xac
   __do_sys_reboot+0xcc/0x1ec
   __arm64_sys_reboot+0x28/0x30
   invoke_syscall+0x4c/0x110
   ...

The issue can also be observed by opening the card with arecord and
then stopping the process through the shell before unbinding:

  # arecord -D hw:UAC2Gadget -f S32_LE -c 2 -r 48000 /dev/null
  Recording WAVE '/dev/null' : Signed 32 bit Little Endian, Rate 48000 Hz, Stereo
  ^Z[1]+  Stopped                    arecord -D hw:UAC2Gadget -f S32_LE -c 2 -r 48000 /dev/null
  # echo gadget.0 > /sys/bus/gadget/drivers/configfs-gadget/unbind
  (observe that the unbind command never finishes)

Fix the problem by using snd_card_free_when_closed() instead, which will
still disconnect the card as desired, but defer the task of freeing the
resources to the core once userspace closes its file descriptor.

Fixes: 132fcb4608 ("usb: gadget: Add Audio Class 2.0 Driver")
Cc: stable@vger.kernel.org
Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Reviewed-by: John Keeping <john@metanate.com>
Link: https://lore.kernel.org/r/20230302163648.3349669-1-alvin@pqrs.dk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2023-03-30 12:49:22 +02:00
arch x86/fpu/xstate: Prevent false-positive warning in __copy_xstate_uabi_buf() 2023-03-30 12:49:21 +02:00
block block: do not reverse request order when flushing plug list 2023-03-22 13:33:46 +01:00
certs certs: Fix build error when PKCS#11 URI contains semicolon 2023-02-09 11:28:11 +01:00
crypto crypto: rsa-pkcs1pad - Use akcipher_request_complete 2023-03-10 09:33:03 +01:00
Documentation docs: Correct missing "d_" prefix for dentry_operations member d_weak_revalidate 2023-03-22 13:33:40 +01:00
drivers usb: gadget: u_audio: don't let userspace block driver unbind 2023-03-30 12:49:22 +02:00
fs cifs: fix dentry lookups in directory handle cache 2023-03-30 12:49:21 +02:00
include entry: Fix noinstr warning in __enter_from_user_mode() 2023-03-30 12:49:13 +02:00
init gcc: disable -Warray-bounds for gcc-11 too 2023-01-14 10:33:43 +01:00
io_uring io_uring/msg_ring: let target know allocated index 2023-03-22 13:34:06 +01:00
ipc ipc: fix memory leak in init_mqueue_fs() 2022-12-31 13:32:01 +01:00
kernel entry/rcu: Check TIF_RESCHED _after_ delayed RCU wake-up 2023-03-30 12:49:13 +02:00
lib sbitmap: Try each queue to wake up at least one waiter 2023-03-10 09:34:34 +01:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: teach mincore_hugetlb about pte markers 2023-03-22 13:34:03 +01:00
net act_mirred: use the backlog for nested calls to mirred ingress 2023-03-30 12:49:20 +02:00
rust rust: print: avoid evaluating arguments in pr_* macros in unsafe blocks 2023-02-06 08:06:34 +01:00
samples ftrace: Export ftrace_free_filter() to modules 2023-02-01 08:34:37 +01:00
scripts kconfig: Update config changed flag before calling callback 2023-03-22 13:33:52 +01:00
security keys: Do not cache key in task struct if key is requested from kernel thread 2023-03-30 12:49:07 +02:00
sound ASoC: amd: yc: Add DMI entries to support HP OMEN 16-n0xxx (8A43) 2023-03-30 12:49:15 +02:00
tools selftests/x86/amx: Add a ptrace test 2023-03-30 12:49:21 +02:00
usr usr/gen_init_cpio.c: remove unnecessary -1 values from int file 2022-10-03 14:21:44 -07:00
virt KVM: Register /dev/kvm as the _very_ last thing during initialization 2023-03-10 09:34:11 +01:00
.clang-format inet: ping: use hlist_nulls rcu iterator during lookup 2022-12-01 12:42:46 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore Kbuild: add Rust support 2022-09-28 09:02:20 +02:00
.mailmap 9 hotfixes. 6 for MM, 3 for other areas. Four of these patches address 2022-12-10 17:10:52 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Remove Michal Marek from Kbuild maintainers 2022-11-16 14:53:00 +09:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS audit: update the mailing list in MAINTAINERS 2023-02-25 11:25:42 +01:00
Makefile Linux 6.1.21 2023-03-22 13:34:07 +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.