From mboxrd@z Thu Jan 1 00:00:00 1970 From: Halil Pasic Subject: [PATCH 1/1] virtio/s390: fix race on airq_areas[] Date: Wed, 24 Jul 2019 00:58:17 +0200 Message-ID: <20190723225817.12800-1-pasic@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Cornelia Huck , kvm@vger.kernel.org, linux-s390@vger.kernel.org Cc: Halil Pasic , Christian Borntraeger , Marc Hartmayer , Janosch Frank , virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org The access to airq_areas was racy ever since the adapter interrupts got introduced to virtio-ccw, but since commit 39c7dcb15892 ("virtio/s390: make airq summary indicators DMA") this became an issue in practice as well. Namely before that commit the airq_info that got overwritten was still functional. After that commit however the two infos share a summary_indicator, which aggravates the situation. Which means auto-online mechanism occasionally hangs the boot with virtio_blk. Signed-off-by: Halil Pasic Reported-by: Marc Hartmayer Fixes: 96b14536d935 ("virtio-ccw: virtio-ccw adapter interrupt support.") --- * We need definitely this fixed for 5.3. For older stable kernels it is to be discussed. @Connie what do you think: do we need a cc stable? * I have a variant that does not need the extra mutex but uses cmpxchg(). Decided to post this one because that one is more complex. But if there is interest we can have a look at it as well. --- drivers/s390/virtio/virtio_ccw.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c index 1a55e5942d36..d97742662755 100644 --- a/drivers/s390/virtio/virtio_ccw.c +++ b/drivers/s390/virtio/virtio_ccw.c @@ -145,6 +145,8 @@ struct airq_info { struct airq_iv *aiv; }; static struct airq_info *airq_areas[MAX_AIRQ_AREAS]; +DEFINE_MUTEX(airq_areas_lock); + static u8 *summary_indicators; static inline u8 *get_summary_indicator(struct airq_info *info) @@ -265,9 +267,11 @@ static unsigned long get_airq_indicator(struct virtqueue *vqs[], int nvqs, unsigned long bit, flags; for (i = 0; i < MAX_AIRQ_AREAS && !indicator_addr; i++) { + mutex_lock(&airq_areas_lock); if (!airq_areas[i]) airq_areas[i] = new_airq_info(i); info = airq_areas[i]; + mutex_unlock(&airq_areas_lock); if (!info) return 0; write_lock_irqsave(&info->lock, flags); -- 2.17.1