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After ptrace_freeze_traced succeeds it is known that the tracee has a __state value of __TASK_TRACED and that no __ptrace_unlink will happen because the tracer is waiting for the tracee, and the tracee is in ptrace_stop. The function ptrace_freeze_traced can succeed at any point after ptrace_stop has set TASK_TRACED and dropped siglock. The read_lock on tasklist_lock only excludes ptrace_attach. This means that the !current->ptrace which executes under a read_lock of tasklist_lock will never see a ptrace_freeze_trace as the tracer must have gone away before the tasklist_lock was taken and ptrace_attach can not occur until the read_lock is dropped. As ptrace_freeze_traced depends upon ptrace_attach running before it can run that excludes ptrace_freeze_traced until __state is set to TASK_RUNNING. This means that task_is_traced will fail in ptrace_freeze_attach and ptrace_freeze_attached will fail. On the current->ptrace branch of ptrace_stop which will be reached any time after ptrace_freeze_traced has succeed it is known that __state is __TASK_TRACED and schedule() will be called with that state. Use a WARN_ON_ONCE to document that wait_task_inactive(TASK_TRACED) should never fail. Remove the stale comment about may_ptrace_stop. Strictly speaking this is not true because if PREEMPT_RT is enabled wait_task_inactive can fail because __state can be changed. I don't see this as a problem as the ptrace code is currently broken on PREMPT_RT, and this is one of the issues. Failing and warning when the assumptions of the code are broken is good. Tested-by: Kees Cook <keescook@chromium.org> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Link: https://lkml.kernel.org/r/20220505182645.497868-8-ebiederm@xmission.com Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
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.