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Syzbot reports a potential deadlock in do_fcntl: ======================================================== WARNING: possible irq lock inversion dependency detected 5.12.0-syzkaller #0 Not tainted -------------------------------------------------------- syz-executor132/8391 just changed the state of lock: ffff888015967bf8 (&f->f_owner.lock){.+..}-{2:2}, at: f_getown_ex fs/fcntl.c:211 [inline] ffff888015967bf8 (&f->f_owner.lock){.+..}-{2:2}, at: do_fcntl+0x8b4/0x1200 fs/fcntl.c:395 but this lock was taken by another, HARDIRQ-safe lock in the past: (&dev->event_lock){-...}-{2:2} and interrupts could create inverse lock ordering between them. other info that might help us debug this: Chain exists of: &dev->event_lock --> &new->fa_lock --> &f->f_owner.lock Possible interrupt unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&f->f_owner.lock); local_irq_disable(); lock(&dev->event_lock); lock(&new->fa_lock); <Interrupt> lock(&dev->event_lock); *** DEADLOCK *** This happens because there is a lock hierarchy of &dev->event_lock --> &new->fa_lock --> &f->f_owner.lock from the following call chain: input_inject_event(): spin_lock_irqsave(&dev->event_lock,...); input_handle_event(): input_pass_values(): input_to_handler(): evdev_events(): evdev_pass_values(): spin_lock(&client->buffer_lock); __pass_event(): kill_fasync(): kill_fasync_rcu(): read_lock(&fa->fa_lock); send_sigio(): read_lock_irqsave(&fown->lock,...); However, since &dev->event_lock is HARDIRQ-safe, interrupts have to be disabled while grabbing &f->f_owner.lock, otherwise we invert the lock hierarchy. Hence, we replace calls to read_lock/read_unlock on &f->f_owner.lock, with read_lock_irq/read_unlock_irq. Reported-and-tested-by: syzbot+e6d5398a02c516ce5e70@syzkaller.appspotmail.com Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com> Signed-off-by: Jeff Layton <jlayton@kernel.org>
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.