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Re: [PATCH] virtiofsd: vu_dispatch locking should never fail
From: |
Vivek Goyal |
Subject: |
Re: [PATCH] virtiofsd: vu_dispatch locking should never fail |
Date: |
Wed, 3 Feb 2021 10:59:34 -0500 |
On Fri, Jan 29, 2021 at 04:53:12PM +0100, Greg Kurz wrote:
> pthread_rwlock_rdlock() and pthread_rwlock_wrlock() can fail if a
> deadlock condition is detected or the current thread already owns
> the lock. They can also fail, like pthread_rwlock_unlock(), if the
> mutex wasn't properly initialized. None of these are ever expected
> to happen with fv_VuDev::vu_dispatch_rwlock.
>
> Some users already check the return value and assert, some others
> don't. Introduce rdlock/wrlock/unlock wrappers that just do the
> former and use them everywhere.
>
> Signed-off-by: Greg Kurz <groug@kaod.org>
> ---
> tools/virtiofsd/fuse_virtio.c | 42 +++++++++++++++++++++++------------
> 1 file changed, 28 insertions(+), 14 deletions(-)
>
> diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
> index ddcefee4272f..7ea269c4b65d 100644
> --- a/tools/virtiofsd/fuse_virtio.c
> +++ b/tools/virtiofsd/fuse_virtio.c
> @@ -187,6 +187,24 @@ static void copy_iov(struct iovec *src_iov, int
> src_count,
> }
> }
>
> +/*
> + * pthread_rwlock_rdlock() and pthread_rwlock_wrlock can fail if
> + * a deadlock condition is detected or the current thread already
> + * owns the lock. They can also fail, like pthread_rwlock_unlock(),
> + * if the mutex wasn't properly initialized. None of these are ever
> + * expected to happen.
> + */
> +#define VU_DISPATCH_LOCK_OP(op) \
> +static inline void vu_dispatch_##op(struct fv_VuDev *vud) \
> +{ \
> + int ret = pthread_rwlock_##op(&vud->vu_dispatch_rwlock); \
> + assert(ret == 0); \
> +}
> +
> +VU_DISPATCH_LOCK_OP(rdlock);
> +VU_DISPATCH_LOCK_OP(wrlock);
> +VU_DISPATCH_LOCK_OP(unlock);
> +
I generally do not prefer using macros to define functions as searching
to functions declarations/definitions becomes harder. But I see lot
of people prefer that because they can reduce number of lines of code.
Apart from that one issue of using rdlock in fv_queue_thread(), stefan
pointed, it looks good to me.
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Vivek
> /*
> * Called back by ll whenever it wants to send a reply/message back
> * The 1st element of the iov starts with the fuse_out_header
> @@ -240,12 +258,12 @@ int virtio_send_msg(struct fuse_session *se, struct
> fuse_chan *ch,
>
> copy_iov(iov, count, in_sg, in_num, tosend_len);
>
> - pthread_rwlock_rdlock(&qi->virtio_dev->vu_dispatch_rwlock);
> + vu_dispatch_rdlock(qi->virtio_dev);
> pthread_mutex_lock(&qi->vq_lock);
> vu_queue_push(dev, q, elem, tosend_len);
> vu_queue_notify(dev, q);
> pthread_mutex_unlock(&qi->vq_lock);
> - pthread_rwlock_unlock(&qi->virtio_dev->vu_dispatch_rwlock);
> + vu_dispatch_unlock(qi->virtio_dev);
>
> req->reply_sent = true;
>
> @@ -403,12 +421,12 @@ int virtio_send_data_iov(struct fuse_session *se,
> struct fuse_chan *ch,
>
> ret = 0;
>
> - pthread_rwlock_rdlock(&qi->virtio_dev->vu_dispatch_rwlock);
> + vu_dispatch_rdlock(qi->virtio_dev);
> pthread_mutex_lock(&qi->vq_lock);
> vu_queue_push(dev, q, elem, tosend_len);
> vu_queue_notify(dev, q);
> pthread_mutex_unlock(&qi->vq_lock);
> - pthread_rwlock_unlock(&qi->virtio_dev->vu_dispatch_rwlock);
> + vu_dispatch_unlock(qi->virtio_dev);
>
> err:
> if (ret == 0) {
> @@ -558,12 +576,12 @@ out:
> fuse_log(FUSE_LOG_DEBUG, "%s: elem %d no reply sent\n", __func__,
> elem->index);
>
> - pthread_rwlock_rdlock(&qi->virtio_dev->vu_dispatch_rwlock);
> + vu_dispatch_rdlock(qi->virtio_dev);
> pthread_mutex_lock(&qi->vq_lock);
> vu_queue_push(dev, q, elem, 0);
> vu_queue_notify(dev, q);
> pthread_mutex_unlock(&qi->vq_lock);
> - pthread_rwlock_unlock(&qi->virtio_dev->vu_dispatch_rwlock);
> + vu_dispatch_unlock(qi->virtio_dev);
> }
>
> pthread_mutex_destroy(&req->ch.lock);
> @@ -596,7 +614,6 @@ static void *fv_queue_thread(void *opaque)
> qi->qidx, qi->kick_fd);
> while (1) {
> struct pollfd pf[2];
> - int ret;
>
> pf[0].fd = qi->kick_fd;
> pf[0].events = POLLIN;
> @@ -645,8 +662,7 @@ static void *fv_queue_thread(void *opaque)
> break;
> }
> /* Mutual exclusion with virtio_loop() */
> - ret = pthread_rwlock_rdlock(&qi->virtio_dev->vu_dispatch_rwlock);
> - assert(ret == 0); /* there is no possible error case */
> + vu_dispatch_wrlock(qi->virtio_dev);
> pthread_mutex_lock(&qi->vq_lock);
> /* out is from guest, in is too guest */
> unsigned int in_bytes, out_bytes;
> @@ -672,7 +688,7 @@ static void *fv_queue_thread(void *opaque)
> }
>
> pthread_mutex_unlock(&qi->vq_lock);
> - pthread_rwlock_unlock(&qi->virtio_dev->vu_dispatch_rwlock);
> + vu_dispatch_unlock(qi->virtio_dev);
>
> /* Process all the requests. */
> if (!se->thread_pool_size && req_list != NULL) {
> @@ -799,7 +815,6 @@ int virtio_loop(struct fuse_session *se)
> while (!fuse_session_exited(se)) {
> struct pollfd pf[1];
> bool ok;
> - int ret;
> pf[0].fd = se->vu_socketfd;
> pf[0].events = POLLIN;
> pf[0].revents = 0;
> @@ -825,12 +840,11 @@ int virtio_loop(struct fuse_session *se)
> assert(pf[0].revents & POLLIN);
> fuse_log(FUSE_LOG_DEBUG, "%s: Got VU event\n", __func__);
> /* Mutual exclusion with fv_queue_thread() */
> - ret = pthread_rwlock_wrlock(&se->virtio_dev->vu_dispatch_rwlock);
> - assert(ret == 0); /* there is no possible error case */
> + vu_dispatch_wrlock(se->virtio_dev);
>
> ok = vu_dispatch(&se->virtio_dev->dev);
>
> - pthread_rwlock_unlock(&se->virtio_dev->vu_dispatch_rwlock);
> + vu_dispatch_unlock(se->virtio_dev);
>
> if (!ok) {
> fuse_log(FUSE_LOG_ERR, "%s: vu_dispatch failed\n", __func__);
> --
> 2.26.2
>