[PATCH v2 4/4] pps: generators: wake up PPS_GEN_FETCHEVENT readers on unregister

[Danish Khateeb <danishkhateeb03@gmail.com>]

A reader sleeping in PPS_GEN_FETCHEVENT waits for the next event, but
no event comes after pps_gen_unregister_source(), so the reader sleeps
until it gets a signal. A PPS_GEN_FETCHEVENT issued after the
unregister sleeps the same way.

Wake up the readers on unregister, and make PPS_GEN_FETCHEVENT fail
with -ENODEV once the generator is gone, like the other ioctls. The
wait checks info without info_lock, so clear it with WRITE_ONCE().

Fixes: 86b525bed275 ("drivers pps: add PPS generators support")
Suggested-by: Rodolfo Giometti <giometti@enneenne.com>
Assisted-by: LLM
Signed-off-by: Danish Khateeb <danishkhateeb03@gmail.com>
---

Notes:
    Tested in the same setup. With a reader asleep in PPS_GEN_FETCHEVENT,
    unbinding the test driver used to leave it asleep until its alarm(5)
    fired (-EINTR after 5 s), and a PPS_GEN_FETCHEVENT after the unbind
    did the same. With this patch both return -ENODEV right away. Normal
    use of pps_gen-dummy, including PPS_GEN_FETCHEVENT, is unchanged.

 drivers/pps/generators/pps_gen.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/pps/generators/pps_gen.c b/drivers/pps/generators/pps_gen.c
index 452cc12a96f2..474e17c36458 100644
--- a/drivers/pps/generators/pps_gen.c
+++ b/drivers/pps/generators/pps_gen.c
@@ -103,11 +103,14 @@ static long pps_gen_cdev_ioctl(struct file *file,
 		dev_dbg(&pps_gen->dev, "PPS_GEN_FETCHEVENT\n");
 
 		ret = wait_event_interruptible(pps_gen->queue,
-				ev != pps_gen->last_ev);
+				ev != pps_gen->last_ev ||
+				!READ_ONCE(pps_gen->info));
 		if (ret == -ERESTARTSYS) {
 			dev_dbg(&pps_gen->dev, "pending signal caught\n");
 			return -EINTR;
 		}
+		if (!READ_ONCE(pps_gen->info))
+			return -ENODEV;
 
 		spin_lock_irq(&pps_gen->lock);
 		info.sequence = pps_gen->sequence;
@@ -238,9 +241,12 @@ static void pps_gen_unregister_cdev(struct pps_gen_device *pps_gen)
 			pps_gen->info->enable(pps_gen, false);
 			pps_gen->enabled = false;
 		}
-		pps_gen->info = NULL;
+		WRITE_ONCE(pps_gen->info, NULL);
 	}
 
+	/* Wake up the readers in PPS_GEN_FETCHEVENT, they fail now as well */
+	wake_up_interruptible_all(&pps_gen->queue);
+
 	put_device(&pps_gen->dev);
 }
 
-- 
2.55.0