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[PULL 1/9] virtiofsd: Release vu_dispatch_lock when stopping queue
From: |
Dr. David Alan Gilbert (git) |
Subject: |
[PULL 1/9] virtiofsd: Release vu_dispatch_lock when stopping queue |
Date: |
Mon, 15 Mar 2021 20:12:07 +0000 |
From: Greg Kurz <groug@kaod.org>
QEMU can stop a virtqueue by sending a VHOST_USER_GET_VRING_BASE request
to virtiofsd. As with all other vhost-user protocol messages, the thread
that runs the main event loop in virtiofsd takes the vu_dispatch lock in
write mode. This ensures that no other thread can access virtqueues or
memory tables at the same time.
In the case of VHOST_USER_GET_VRING_BASE, the main thread basically
notifies the queue thread that it should terminate and waits for its
termination:
main()
virtio_loop()
vu_dispatch_wrlock()
vu_dispatch()
vu_process_message()
vu_get_vring_base_exec()
fv_queue_cleanup_thread()
pthread_join()
Unfortunately, the queue thread ends up calling virtio_send_msg()
at some point, which itself needs to grab the lock:
fv_queue_thread()
g_list_foreach()
fv_queue_worker()
fuse_session_process_buf_int()
do_release()
lo_release()
fuse_reply_err()
send_reply()
send_reply_iov()
fuse_send_reply_iov_nofree()
fuse_send_msg()
virtio_send_msg()
vu_dispatch_rdlock() <-- Deadlock !
Simply have the main thread to release the lock before going to
sleep and take it back afterwards. A very similar patch was already
sent by Vivek Goyal sometime back:
https://listman.redhat.com/archives/virtio-fs/2021-January/msg00073.html
The only difference here is that this done in fv_queue_set_started()
because fv_queue_cleanup_thread() can also be called from virtio_loop()
without the lock being held.
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20210312092212.782255-8-groug@kaod.org>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
tools/virtiofsd/fuse_virtio.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
index 523ee64fb7..3e13997406 100644
--- a/tools/virtiofsd/fuse_virtio.c
+++ b/tools/virtiofsd/fuse_virtio.c
@@ -792,7 +792,13 @@ static void fv_queue_set_started(VuDev *dev, int qidx,
bool started)
assert(0);
}
} else {
+ /*
+ * Temporarily drop write-lock taken in virtio_loop() so that
+ * the queue thread doesn't block in virtio_send_msg().
+ */
+ vu_dispatch_unlock(vud);
fv_queue_cleanup_thread(vud, qidx);
+ vu_dispatch_wrlock(vud);
}
}
--
2.30.2
- [PULL 0/9] virtiofs and migration queue, Dr. David Alan Gilbert (git), 2021/03/15
- [PULL 1/9] virtiofsd: Release vu_dispatch_lock when stopping queue,
Dr. David Alan Gilbert (git) <=
- [PULL 2/9] virtiofsd: Add qemu version and copyright info, Dr. David Alan Gilbert (git), 2021/03/15
- [PULL 3/9] virtiofsd: Don't allow empty filenames, Dr. David Alan Gilbert (git), 2021/03/15
- [PULL 4/9] virtiofsd: Don't allow empty paths in lookup_name(), Dr. David Alan Gilbert (git), 2021/03/15
- [PULL 7/9] migration/tls: add error handling in multifd_tls_handshake_thread, Dr. David Alan Gilbert (git), 2021/03/15
- [PULL 5/9] virtiofsd: Convert some functions to return bool, Dr. David Alan Gilbert (git), 2021/03/15
- [PULL 8/9] monitor: Replaced qemu_mutex_lock calls with QEMU_LOCK_GUARD, Dr. David Alan Gilbert (git), 2021/03/15
- [PULL 6/9] migration/tls: fix inverted semantics in multifd_channel_connect, Dr. David Alan Gilbert (git), 2021/03/15
- [PULL 9/9] migration: Replaced qemu_mutex_lock calls with QEMU_LOCK_GUARD, Dr. David Alan Gilbert (git), 2021/03/15
- Re: [PULL 0/9] virtiofs and migration queue, Peter Maydell, 2021/03/17