This is a note to let you know that I've just added the patch titled s390/ap: Fix hanging ioctl caused by orphaned replies to the 5.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: s390-ap-fix-hanging-ioctl-caused-by-orphaned-replies.patch and it can be found in the queue-5.15 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 3826350e6dd435e244eb6e47abad5a47c169ebc2 Mon Sep 17 00:00:00 2001 From: Harald Freudenberger <freude@xxxxxxxxxxxxx> Date: Thu, 14 Oct 2021 09:58:24 +0200 Subject: s390/ap: Fix hanging ioctl caused by orphaned replies From: Harald Freudenberger <freude@xxxxxxxxxxxxx> commit 3826350e6dd435e244eb6e47abad5a47c169ebc2 upstream. When a queue is switched to soft offline during heavy load and later switched to soft online again and now used, it may be that the caller is blocked forever in the ioctl call. The failure occurs because there is a pending reply after the queue(s) have been switched to offline. This orphaned reply is received when the queue is switched to online and is accidentally counted for the outstanding replies. So when there was a valid outstanding reply and this orphaned reply is received it counts as the outstanding one thus dropping the outstanding counter to 0. Voila, with this counter the receive function is not called any more and the real outstanding reply is never received (until another request comes in...) and the ioctl blocks. The fix is simple. However, instead of readjusting the counter when an orphaned reply is detected, I check the queue status for not empty and compare this to the outstanding counter. So if the queue is not empty then the counter must not drop to 0 but at least have a value of 1. Signed-off-by: Harald Freudenberger <freude@xxxxxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/s390/crypto/ap_queue.c | 2 ++ 1 file changed, 2 insertions(+) --- a/drivers/s390/crypto/ap_queue.c +++ b/drivers/s390/crypto/ap_queue.c @@ -157,6 +157,8 @@ static struct ap_queue_status ap_sm_recv switch (status.response_code) { case AP_RESPONSE_NORMAL: aq->queue_count = max_t(int, 0, aq->queue_count - 1); + if (!status.queue_empty && !aq->queue_count) + aq->queue_count++; if (aq->queue_count > 0) mod_timer(&aq->timeout, jiffies + aq->request_timeout); Patches currently in stable-queue which might be from freude@xxxxxxxxxxxxx are queue-5.15/s390-ap-fix-hanging-ioctl-caused-by-orphaned-replies.patch