From 4617721c502b2ddaa4e324e86da4997edf738fa5 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 2 Sep 2026 09:55:01 -0400 Subject: ftrace: Synchronize the initialization of ftrace_ops 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 --- Documentation/filesystems/devpts.rst | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) create mode 100644 Documentation/filesystems/devpts.rst (limited to 'Documentation/filesystems/devpts.rst') diff --git a/Documentation/filesystems/devpts.rst b/Documentation/filesystems/devpts.rst new file mode 100644 index 000000000..b6324ab19 --- /dev/null +++ b/Documentation/filesystems/devpts.rst @@ -0,0 +1,36 @@ +.. SPDX-License-Identifier: GPL-2.0 + +===================== +The Devpts Filesystem +===================== + +Each mount of the devpts filesystem is now distinct such that ptys +and their indices allocated in one mount are independent from ptys +and their indices in all other mounts. + +All mounts of the devpts filesystem now create a ``/dev/pts/ptmx`` node +with permissions ``0000``. + +To retain backwards compatibility the a ptmx device node (aka any node +created with ``mknod name c 5 2``) when opened will look for an instance +of devpts under the name ``pts`` in the same directory as the ptmx device +node. + +As an option instead of placing a ``/dev/ptmx`` device node at ``/dev/ptmx`` +it is possible to place a symlink to ``/dev/pts/ptmx`` at ``/dev/ptmx`` or +to bind mount ``/dev/ptx/ptmx`` to ``/dev/ptmx``. If you opt for using +the devpts filesystem in this manner devpts should be mounted with +the ``ptmxmode=0666``, or ``chmod 0666 /dev/pts/ptmx`` should be called. + +Total count of pty pairs in all instances is limited by sysctls:: + + kernel.pty.max = 4096 - global limit + kernel.pty.reserve = 1024 - reserved for filesystems mounted from the initial mount namespace + kernel.pty.nr - current count of ptys + +Per-instance limit could be set by adding mount option ``max=``. + +This feature was added in kernel 3.4 together with +``sysctl kernel.pty.reserve``. + +In kernels older than 3.4 sysctl ``kernel.pty.max`` works as per-instance limit. -- cgit v1.3.1