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4f07ec0d76
The recent rework of the requeue PI code introduced a possibility for
going back to user space in inconsistent state:
CPU 0 CPU 1
requeue_futex()
if (lock_pifutex_user()) {
dequeue_waiter();
wake_waiter(task);
sched_in(task);
return_from_futex_syscall();
---> Inconsistent state because PI state is not established
It becomes worse if the woken up task immediately exits:
sys_exit();
attach_pistate(vpid); <--- FAIL
Attach the pi state before dequeuing and waking the waiter. If the waiter
gets a spurious wakeup before the dequeue operation it will wait in
futex_requeue_pi_wakeup_sync() and therefore cannot return and exit.
Fixes: 07d91ef510 ("futex: Prevent requeue_pi() lock nesting issue on RT")
Reported-by: syzbot+4d1bd0725ef09168e1a0@syzkaller.appspotmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210902094414.558914045@linutronix.de
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.