Re: [dpdk-dev] [PATCH v2] vhost: fix vid allocation race
From: Xia, Chenbo <hidden>
Date: 2021-02-03 02:44:59
Hi Peng,
-----Original Message-----
From: Peng He <redacted>
Sent: Monday, February 1, 2021 4:49 PM
To: dev@dpdk.org; Xia, Chenbo <redacted>
Cc: stable@dpdk.org
Subject: [PATCH v2] vhost: fix vid allocation race
vhost_new_device might be called in different threads at the same time.
thread 1(config thread)
rte_vhost_driver_start
->vhost_user_start_client
->vhost_user_add_connection
-> vhost_new_device
thread 2(vhost-events)
vhost_user_read_cb
->vhost_user_msg_handler (return value < 0)
-> vhost_user_start_client
-> vhost_new_device
So there could be a case that a same vid has been allocated twice, or
some vid might be lost in DPDK lib however still held by the upper
applications.
Another place where race would happen is at the func *vhost_destroy_device*,
but after a detailed investigation, the race does not exist as long as
no two devices have the same vid: Calling vhost_destroy_devices in
different threads with different vids is actually safe.I want to clarify another thing, vhost_destroy_device and get_device may have a thread-safe problem. That is: vhost_user_read_cb() destroys the device while app thread is calling vhost API (with get_device in it) to use that device. A good thing is before vhost_user_read_cb() destroys the device, it notifies the app thread, so vhost app should make sure it avoids this kind of problem. Otherwise we may need to lock all places that uses the global vhost_devices, which is not good since that will affect data path perf a lot. Anyway, your patch fixes the specific problem you mentioned. For this patch: Reviewed-by: Chenbo Xia <redacted>
quoted hunk ↗ jump to hunk
Fixes: a277c715987 ("vhost: refactor code structure") Reported-by: Peng He <redacted> Signed-off-by: Fei Chen <redacted> Reviewed-by: Zhihong Wang <redacted> --- lib/librte_vhost/vhost.c | 6 ++++++ 1 file changed, 6 insertions(+)diff --git a/lib/librte_vhost/vhost.c b/lib/librte_vhost/vhost.c index efb136edd1..52ab93d1ec 100644 --- a/lib/librte_vhost/vhost.c +++ b/lib/librte_vhost/vhost.c@@ -26,6 +26,7 @@ #include "vhost_user.h" struct virtio_net *vhost_devices[MAX_VHOST_DEVICE]; +pthread_mutex_t vhost_dev_lock = PTHREAD_MUTEX_INITIALIZER; /* Called with iotlb_lock read-locked */ uint64_t@@ -645,6 +646,7 @@ vhost_new_device(void) struct virtio_net *dev; int i; + pthread_mutex_lock(&vhost_dev_lock); for (i = 0; i < MAX_VHOST_DEVICE; i++) { if (vhost_devices[i] == NULL) break;@@ -653,6 +655,7 @@ vhost_new_device(void) if (i == MAX_VHOST_DEVICE) { VHOST_LOG_CONFIG(ERR, "Failed to find a free slot for new device.\n"); + pthread_mutex_unlock(&vhost_dev_lock); return -1; }@@ -660,10 +663,13 @@ vhost_new_device(void) if (dev == NULL) { VHOST_LOG_CONFIG(ERR, "Failed to allocate memory for new dev.\n"); + pthread_mutex_unlock(&vhost_dev_lock); return -1; } vhost_devices[i] = dev; + pthread_mutex_unlock(&vhost_dev_lock); + dev->vid = i; dev->flags = VIRTIO_DEV_BUILTIN_VIRTIO_NET; dev->slave_req_fd = -1; --2.23.0