Input: uinput - avoid FF flush when destroying device

Normally, when input device supporting force feedback effects is being
destroyed, we try to "flush" currently playing effects, so that the
physical device does not continue vibrating (or executing other effects).
Unfortunately this does not work well for uinput as flushing of the effects
deadlocks with the destroy action:

- if device is being destroyed because the file descriptor is being closed,
  then there is noone to even service FF requests;

- if device is being destroyed because userspace sent UI_DEV_DESTROY,
  while theoretically it could be possible to service FF requests,
  userspace is unlikely to do so (they'd need to make sure FF handling
  happens on a separate thread) even if kernel solves the issue with FF
  ioctls deadlocking with UI_DEV_DESTROY ioctl on udev->mutex.

To avoid lockups like the one below, let's install a custom input device
flush handler, and avoid trying to flush force feedback effects when we
destroying the device, and instead rely on uinput to shut off the device
properly.

NMI watchdog: Watchdog detected hard LOCKUP on cpu 3
...
 <<EOE>>  [<ffffffff817a0307>] _raw_spin_lock_irqsave+0x37/0x40
 [<ffffffff810e633d>] complete+0x1d/0x50
 [<ffffffffa00ba08c>] uinput_request_done+0x3c/0x40 [uinput]
 [<ffffffffa00ba587>] uinput_request_submit.part.7+0x47/0xb0 [uinput]
 [<ffffffffa00bb62b>] uinput_dev_erase_effect+0x5b/0x76 [uinput]
 [<ffffffff815d91ad>] erase_effect+0xad/0xf0
 [<ffffffff815d929d>] flush_effects+0x4d/0x90
 [<ffffffff815d4cc0>] input_flush_device+0x40/0x60
 [<ffffffff815daf1c>] evdev_cleanup+0xac/0xc0
 [<ffffffff815daf5b>] evdev_disconnect+0x2b/0x60
 [<ffffffff815d74ac>] __input_unregister_device+0xac/0x150
 [<ffffffff815d75f7>] input_unregister_device+0x47/0x70
 [<ffffffffa00bac45>] uinput_destroy_device+0xb5/0xc0 [uinput]
 [<ffffffffa00bb2de>] uinput_ioctl_handler.isra.9+0x65e/0x740 [uinput]
 [<ffffffff811231ab>] ? do_futex+0x12b/0xad0
 [<ffffffffa00bb3f8>] uinput_ioctl+0x18/0x20 [uinput]
 [<ffffffff81241248>] do_vfs_ioctl+0x298/0x480
 [<ffffffff81337553>] ? security_file_ioctl+0x43/0x60
 [<ffffffff812414a9>] SyS_ioctl+0x79/0x90
 [<ffffffff817a04ee>] entry_SYSCALL_64_fastpath+0x12/0x71

Reported-by: Rodrigo Rivas Costa <rodrigorivascosta@gmail.com>
Reported-by: Clément VUCHENER <clement.vuchener@gmail.com>
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=193741
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 18 insertions, 0 deletions

diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c
index 022be0e22eba..2cff40be8860 100644
--- a/drivers/input/misc/uinput.c
+++ b/drivers/input/misc/uinput.c
@@ -230,6 +230,18 @@ static int uinput_dev_erase_effect(struct input_dev *dev, int effect_id)
 	return uinput_request_submit(udev, &request);
 }
 
+static int uinput_dev_flush(struct input_dev *dev, struct file *file)
+{
+	/*
+	 * If we are called with file == NULL that means we are tearing
+	 * down the device, and therefore we can not handle FF erase
+	 * requests: either we are handling UI_DEV_DESTROY (and holding
+	 * the udev->mutex), or the file descriptor is closed and there is
+	 * nobody on the other side anymore.
+	 */
+	return file ? input_ff_flush(dev, file) : 0;
+}
+
 static void uinput_destroy_device(struct uinput_device *udev)
 {
 	const char *name, *phys;
@@ -297,6 +309,12 @@ static int uinput_create_device(struct uinput_device *udev)
 		dev->ff->playback = uinput_dev_playback;
 		dev->ff->set_gain = uinput_dev_set_gain;
 		dev->ff->set_autocenter = uinput_dev_set_autocenter;
+		/*
+		 * The standard input_ff_flush() implementation does
+		 * not quite work for uinput as we can't reasonably
+		 * handle FF requests during device teardown.
+		 */
+		dev->flush = uinput_dev_flush;
 	}
 
 	error = input_register_device(udev->dev);