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[PATCH 087/104] virtiofsd: prevent fv_queue_thread() vs virtio_loop() ra
From: |
Dr. David Alan Gilbert (git) |
Subject: |
[PATCH 087/104] virtiofsd: prevent fv_queue_thread() vs virtio_loop() races |
Date: |
Thu, 12 Dec 2019 16:38:47 +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>
Merged with log changes
pull request 12
---
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 a364f23d5d..2c1e524852 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
@@ -413,6 +425,8 @@ 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;
@@ -459,6 +473,9 @@ 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);
@@ -467,6 +484,7 @@ 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;
@@ -595,6 +613,8 @@ 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);
@@ -701,6 +721,8 @@ 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;
@@ -725,7 +747,15 @@ 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;
}
@@ -871,6 +901,7 @@ 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);
@@ -887,6 +918,7 @@ void virtio_session_close(struct fuse_session *se)
close(se->vu_socketfd);
free(se->virtio_dev->qi);
+ pthread_rwlock_destroy(&se->virtio_dev->vu_dispatch_rwlock);
free(se->virtio_dev);
se->virtio_dev = NULL;
}
--
2.23.0
- [PATCH 077/104] virtiofsd: fix error handling in main(), (continued)
- [PATCH 077/104] virtiofsd: fix error handling in main(), Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 078/104] virtiofsd: cleanup allocated resource in se, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 079/104] virtiofsd: fix memory leak on lo.source, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 080/104] virtiofsd: add helper for lo_data cleanup, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 081/104] virtiofsd: Prevent multiply running with same vhost_user_socket, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 082/104] virtiofsd: enable PARALLEL_DIROPS during INIT, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 084/104] Virtiofsd: fix memory leak on fuse queueinfo, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 083/104] virtiofsd: fix incorrect error handling in lo_do_lookup, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 086/104] virtiofsd: use fuse_lowlevel_is_virtio() in fuse_session_destroy(), Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 085/104] virtiofsd: Support remote posix locks, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 087/104] virtiofsd: prevent fv_queue_thread() vs virtio_loop() races,
Dr. David Alan Gilbert (git) <=
- [PATCH 089/104] virtiofsd: prevent races with lo_dirp_put(), Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 088/104] virtiofsd: make lo_release() atomic, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 091/104] libvhost-user: Fix some memtable remap cases, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 090/104] virtiofsd: rename inode->refcount to inode->nlookup, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 092/104] virtiofsd: add man page, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 094/104] virtiofsd: do not always set FUSE_FLOCK_LOCKS, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 095/104] virtiofsd: convert more fprintf and perror to use fuse log infra, Dr. David Alan Gilbert (git), 2019/12/12
- [PATCH 093/104] virtiofsd: introduce inode refcount to prevent use-after-free, Dr. David Alan Gilbert (git), 2019/12/12