ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 132 insertions, 0 deletions

diff --git a/Documentation/usb/acm.rst b/Documentation/usb/acm.rst
new file mode 100644
index 000000000..e8bda98e9
--- /dev/null
+++ b/Documentation/usb/acm.rst
@@ -0,0 +1,132 @@
+======================
+Linux ACM driver v0.16
+======================
+
+Copyright (c) 1999 Vojtech Pavlik <vojtech@suse.cz>
+
+Sponsored by SuSE
+
+0. Disclaimer
+~~~~~~~~~~~~~
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 2 of the License, or (at your option)
+any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+more details.
+
+You should have received a copy of the GNU General Public License along
+with this program; if not, write to the Free Software Foundation, Inc., 59
+Temple Place, Suite 330, Boston, MA 02111-1307 USA
+
+Should you need to contact me, the author, you can do so either by e-mail -
+mail your message to <vojtech@suse.cz>, or by paper mail: Vojtech Pavlik,
+Ucitelska 1576, Prague 8, 182 00 Czech Republic
+
+For your convenience, the GNU General Public License version 2 is included
+in the package: See the file COPYING.
+
+1. Usage
+~~~~~~~~
+The drivers/usb/class/cdc-acm.c drivers works with USB modems and USB ISDN terminal
+adapters that conform to the Universal Serial Bus Communication Device Class
+Abstract Control Model (USB CDC ACM) specification.
+
+Many modems do, here is a list of those I know of:
+
+	- 3Com OfficeConnect 56k
+	- 3Com Voice FaxModem Pro
+	- 3Com Sportster
+	- MultiTech MultiModem 56k
+	- Zoom 2986L FaxModem
+	- Compaq 56k FaxModem
+	- ELSA Microlink 56k
+
+I know of one ISDN TA that does work with the acm driver:
+
+	- 3Com USR ISDN Pro TA
+
+Some cell phones also connect via USB. I know the following phones work:
+
+	- SonyEricsson K800i
+
+Unfortunately many modems and most ISDN TAs use proprietary interfaces and
+thus won't work with this drivers. Check for ACM compliance before buying.
+
+To use the modems you need these modules loaded::
+
+	usbcore.ko
+	uhci-hcd.ko ohci-hcd.ko or ehci-hcd.ko
+	cdc-acm.ko
+
+After that, the modem[s] should be accessible. You should be able to use
+minicom, ppp and mgetty with them.
+
+2. Verifying that it works
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The first step would be to check /sys/kernel/debug/usb/devices, it should look
+like this::
+
+  T:  Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#=  1 Spd=12  MxCh= 2
+  B:  Alloc=  0/900 us ( 0%), #Int=  0, #Iso=  0
+  D:  Ver= 1.00 Cls=09(hub  ) Sub=00 Prot=00 MxPS= 8 #Cfgs=  1
+  P:  Vendor=0000 ProdID=0000 Rev= 0.00
+  S:  Product=USB UHCI Root Hub
+  S:  SerialNumber=6800
+  C:* #Ifs= 1 Cfg#= 1 Atr=40 MxPwr=  0mA
+  I:  If#= 0 Alt= 0 #EPs= 1 Cls=09(hub  ) Sub=00 Prot=00 Driver=hub
+  E:  Ad=81(I) Atr=03(Int.) MxPS=   8 Ivl=255ms
+  T:  Bus=01 Lev=01 Prnt=01 Port=01 Cnt=01 Dev#=  2 Spd=12  MxCh= 0
+  D:  Ver= 1.00 Cls=02(comm.) Sub=00 Prot=00 MxPS= 8 #Cfgs=  2
+  P:  Vendor=04c1 ProdID=008f Rev= 2.07
+  S:  Manufacturer=3Com Inc.
+  S:  Product=3Com U.S. Robotics Pro ISDN TA
+  S:  SerialNumber=UFT53A49BVT7
+  C:  #Ifs= 1 Cfg#= 1 Atr=60 MxPwr=  0mA
+  I:  If#= 0 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=ff Prot=ff Driver=acm
+  E:  Ad=85(I) Atr=02(Bulk) MxPS=  64 Ivl=  0ms
+  E:  Ad=04(O) Atr=02(Bulk) MxPS=  64 Ivl=  0ms
+  E:  Ad=81(I) Atr=03(Int.) MxPS=  16 Ivl=128ms
+  C:* #Ifs= 2 Cfg#= 2 Atr=60 MxPwr=  0mA
+  I:  If#= 0 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=02 Prot=01 Driver=acm
+  E:  Ad=81(I) Atr=03(Int.) MxPS=  16 Ivl=128ms
+  I:  If#= 1 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=acm
+  E:  Ad=85(I) Atr=02(Bulk) MxPS=  64 Ivl=  0ms
+  E:  Ad=04(O) Atr=02(Bulk) MxPS=  64 Ivl=  0ms
+
+The presence of these three lines (and the Cls= 'comm' and 'data' classes)
+is important, it means it's an ACM device. The Driver=acm means the acm
+driver is used for the device. If you see only Cls=ff(vend.) then you're out
+of luck, you have a device with vendor specific-interface::
+
+  D:  Ver= 1.00 Cls=02(comm.) Sub=00 Prot=00 MxPS= 8 #Cfgs=  2
+  I:  If#= 0 Alt= 0 #EPs= 1 Cls=02(comm.) Sub=02 Prot=01 Driver=acm
+  I:  If#= 1 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=acm
+
+In the system log you should see::
+
+  usb.c: USB new device connect, assigned device number 2
+  usb.c: kmalloc IF c7691fa0, numif 1
+  usb.c: kmalloc IF c7b5f3e0, numif 2
+  usb.c: skipped 4 class/vendor specific interface descriptors
+  usb.c: new device strings: Mfr=1, Product=2, SerialNumber=3
+  usb.c: USB device number 2 default language ID 0x409
+  Manufacturer: 3Com Inc.
+  Product: 3Com U.S. Robotics Pro ISDN TA
+  SerialNumber: UFT53A49BVT7
+  acm.c: probing config 1
+  acm.c: probing config 2
+  ttyACM0: USB ACM device
+  acm.c: acm_control_msg: rq: 0x22 val: 0x0 len: 0x0 result: 0
+  acm.c: acm_control_msg: rq: 0x20 val: 0x0 len: 0x7 result: 7
+  usb.c: acm driver claimed interface c7b5f3e0
+  usb.c: acm driver claimed interface c7b5f3f8
+  usb.c: acm driver claimed interface c7691fa0
+
+If all this seems to be OK, fire up minicom and set it to talk to the ttyACM
+device and try typing 'at'. If it responds with 'OK', then everything is
+working.