diff options
author | Kevin Wolf <kwolf@redhat.com> | 2024-03-14 17:58:24 +0100 |
---|---|---|
committer | Kevin Wolf <kwolf@redhat.com> | 2024-03-18 12:38:02 +0100 |
commit | 9c707525cbb1dd1e56876e45c70c0c08f2876d41 (patch) | |
tree | 1670192108968d8efaafd8246ea0710678e4a81b /nbd/server.c | |
parent | ae5a40e8581185654a667fbbf7e4adbc2a2a3e45 (diff) |
nbd/server: Fix race in draining the export
When draining an NBD export, nbd_drained_begin() first sets
client->quiescing so that nbd_client_receive_next_request() won't start
any new request coroutines. Then nbd_drained_poll() tries to makes sure
that we wait for any existing request coroutines by checking that
client->nb_requests has become 0.
However, there is a small window between creating a new request
coroutine and increasing client->nb_requests. If a coroutine is in this
state, it won't be waited for and drain returns too early.
In the context of switching to a different AioContext, this means that
blk_aio_attached() will see client->recv_coroutine != NULL and fail its
assertion.
Fix this by increasing client->nb_requests immediately when starting the
coroutine. Doing this after the checks if we should create a new
coroutine is okay because client->lock is held.
Cc: qemu-stable@nongnu.org
Fixes: fd6afc501a01 ("nbd/server: Use drained block ops to quiesce the server")
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20240314165825.40261-2-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'nbd/server.c')
-rw-r--r-- | nbd/server.c | 15 |
1 files changed, 7 insertions, 8 deletions
diff --git a/nbd/server.c b/nbd/server.c index 941832f178..c3484cc1eb 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -3007,8 +3007,8 @@ static coroutine_fn int nbd_handle_request(NBDClient *client, /* Owns a reference to the NBDClient passed as opaque. */ static coroutine_fn void nbd_trip(void *opaque) { - NBDClient *client = opaque; - NBDRequestData *req = NULL; + NBDRequestData *req = opaque; + NBDClient *client = req->client; NBDRequest request = { 0 }; /* GCC thinks it can be used uninitialized */ int ret; Error *local_err = NULL; @@ -3037,8 +3037,6 @@ static coroutine_fn void nbd_trip(void *opaque) goto done; } - req = nbd_request_get(client); - /* * nbd_co_receive_request() returns -EAGAIN when nbd_drained_begin() has * set client->quiescing but by the time we get back nbd_drained_end() may @@ -3112,9 +3110,7 @@ static coroutine_fn void nbd_trip(void *opaque) } done: - if (req) { - nbd_request_put(req); - } + nbd_request_put(req); qemu_mutex_unlock(&client->lock); @@ -3143,10 +3139,13 @@ disconnect: */ static void nbd_client_receive_next_request(NBDClient *client) { + NBDRequestData *req; + if (!client->recv_coroutine && client->nb_requests < MAX_NBD_REQUESTS && !client->quiescing) { nbd_client_get(client); - client->recv_coroutine = qemu_coroutine_create(nbd_trip, client); + req = nbd_request_get(client); + client->recv_coroutine = qemu_coroutine_create(nbd_trip, req); aio_co_schedule(client->exp->common.ctx, client->recv_coroutine); } } |