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[PULL 087/108] virtiofsd: prevent fv_queue_thread() vs virtio_loop() rac
From: |
Dr. David Alan Gilbert (git) |
Subject: |
[PULL 087/108] virtiofsd: prevent fv_queue_thread() vs virtio_loop() races |
Date: |
Thu, 23 Jan 2020 16:46:09 +0000 |
From: Stefan Hajnoczi <address@hidden>
We call into libvhost-user from the virtqueue handler thread and the
vhost-user message processing thread without a lock. There is nothing
protecting the virtqueue handler thread if the vhost-user message
processing thread changes the virtqueue or memory table while it is
running.
This patch introduces a read-write lock. Virtqueue handler threads are
readers. The vhost-user message processing thread is a writer. This
will allow concurrency for multiqueue in the future while protecting
against fv_queue_thread() vs virtio_loop() races.
Note that the critical sections could be made smaller but it would be
more invasive and require libvhost-user changes. Let's start simple and
improve performance later, if necessary. Another option would be an
RCU-style approach with lighter-weight primitives.
Signed-off-by: Stefan Hajnoczi <address@hidden>
Reviewed-by: Daniel P. Berrangé <address@hidden>
Signed-off-by: Dr. David Alan Gilbert <address@hidden>
---
tools/virtiofsd/fuse_virtio.c | 34 +++++++++++++++++++++++++++++++++-
1 file changed, 33 insertions(+), 1 deletion(-)
diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
index fb8d6d1379..f6242f9338 100644
--- a/tools/virtiofsd/fuse_virtio.c
+++ b/tools/virtiofsd/fuse_virtio.c
@@ -58,6 +58,18 @@ struct fv_VuDev {
VuDev dev;
struct fuse_session *se;
+ /*
+ * Either handle virtqueues or vhost-user protocol messages. Don't do
+ * both at the same time since that could lead to race conditions if
+ * virtqueues or memory tables change while another thread is accessing
+ * them.
+ *
+ * The assumptions are:
+ * 1. fv_queue_thread() reads/writes to virtqueues and only reads VuDev.
+ * 2. virtio_loop() reads/writes virtqueues and VuDev.
+ */
+ pthread_rwlock_t vu_dispatch_rwlock;
+
/*
* The following pair of fields are only accessed in the main
* virtio_loop
@@ -415,6 +427,8 @@ 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;
pf[0].revents = 0;
@@ -461,6 +475,9 @@ static void *fv_queue_thread(void *opaque)
fuse_log(FUSE_LOG_ERR, "Eventfd_read for queue: %m\n");
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 */
/* out is from guest, in is too guest */
unsigned int in_bytes, out_bytes;
vu_queue_get_avail_bytes(dev, q, &in_bytes, &out_bytes, ~0, ~0);
@@ -469,6 +486,7 @@ static void *fv_queue_thread(void *opaque)
"%s: Queue %d gave evalue: %zx available: in: %u out: %u\n",
__func__, qi->qidx, (size_t)evalue, in_bytes, out_bytes);
+
while (1) {
bool allocated_bufv = false;
struct fuse_bufvec bufv;
@@ -597,6 +615,8 @@ static void *fv_queue_thread(void *opaque)
free(elem);
elem = NULL;
}
+
+ pthread_rwlock_unlock(&qi->virtio_dev->vu_dispatch_rwlock);
}
out:
pthread_mutex_destroy(&ch.lock);
@@ -711,6 +731,8 @@ 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;
@@ -735,7 +757,15 @@ int virtio_loop(struct fuse_session *se)
}
assert(pf[0].revents & POLLIN);
fuse_log(FUSE_LOG_DEBUG, "%s: Got VU event\n", __func__);
- if (!vu_dispatch(&se->virtio_dev->dev)) {
+ /* 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 */
+
+ ok = vu_dispatch(&se->virtio_dev->dev);
+
+ pthread_rwlock_unlock(&se->virtio_dev->vu_dispatch_rwlock);
+
+ if (!ok) {
fuse_log(FUSE_LOG_ERR, "%s: vu_dispatch failed\n", __func__);
break;
}
@@ -877,6 +907,7 @@ int virtio_session_mount(struct fuse_session *se)
se->vu_socketfd = data_sock;
se->virtio_dev->se = se;
+ pthread_rwlock_init(&se->virtio_dev->vu_dispatch_rwlock, NULL);
vu_init(&se->virtio_dev->dev, 2, se->vu_socketfd, fv_panic, fv_set_watch,
fv_remove_watch, &fv_iface);
@@ -892,6 +923,7 @@ void virtio_session_close(struct fuse_session *se)
}
free(se->virtio_dev->qi);
+ pthread_rwlock_destroy(&se->virtio_dev->vu_dispatch_rwlock);
free(se->virtio_dev);
se->virtio_dev = NULL;
}
--
2.24.1
- [PULL 080/108] virtiofsd: add helper for lo_data cleanup, (continued)
- [PULL 080/108] virtiofsd: add helper for lo_data cleanup, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 078/108] virtiofsd: cleanup allocated resource in se, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 079/108] virtiofsd: fix memory leak on lo.source, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 081/108] virtiofsd: Prevent multiply running with same vhost_user_socket, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 082/108] virtiofsd: enable PARALLEL_DIROPS during INIT, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 083/108] virtiofsd: fix incorrect error handling in lo_do_lookup, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 084/108] Virtiofsd: fix memory leak on fuse queueinfo, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 086/108] virtiofsd: use fuse_lowlevel_is_virtio() in fuse_session_destroy(), Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 085/108] virtiofsd: Support remote posix locks, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 088/108] virtiofsd: make lo_release() atomic, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 087/108] virtiofsd: prevent fv_queue_thread() vs virtio_loop() races,
Dr. David Alan Gilbert (git) <=
- [PULL 090/108] virtiofsd: rename inode->refcount to inode->nlookup, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 089/108] virtiofsd: prevent races with lo_dirp_put(), Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 091/108] libvhost-user: Fix some memtable remap cases, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 092/108] virtiofsd: passthrough_ll: fix refcounting on remove/rename, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 097/108] virtiofsd: Fix data corruption with O_APPEND write in writeback mode, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 096/108] virtiofsd: Reset O_DIRECT flag during file open, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 095/108] virtiofsd: convert more fprintf and perror to use fuse log infra, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 094/108] virtiofsd: do not always set FUSE_FLOCK_LOCKS, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 093/108] virtiofsd: introduce inode refcount to prevent use-after-free, Dr. David Alan Gilbert (git), 2020/01/23
- [PULL 098/108] virtiofsd: passthrough_ll: Use cache_readdir for directory open, Dr. David Alan Gilbert (git), 2020/01/23