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Re: [PATCH v4] nbd/server: do not poll within a coroutine context
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From: |
Vladimir Sementsov-Ogievskiy |
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Subject: |
Re: [PATCH v4] nbd/server: do not poll within a coroutine context |
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Date: |
Mon, 8 Apr 2024 11:46:39 +0300 |
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User-agent: |
Mozilla Thunderbird |
On 05.04.24 20:44, Eric Blake wrote:
From: Zhu Yangyang <zhuyangyang14@huawei.com>
Coroutines are not supposed to block. Instead, they should yield.
The client performs TLS upgrade outside of an AIOContext, during
synchronous handshake; this still requires g_main_loop. But the
server responds to TLS upgrade inside a coroutine, so a nested
g_main_loop is wrong. Since the two callbacks no longer share more
than the setting of data.complete and data.error, it's just as easy to
use static helpers instead of trying to share a common code path.
Fixes: f95910f ("nbd: implement TLS support in the protocol negotiation")
Signed-off-by: Zhu Yangyang <zhuyangyang14@huawei.com>
[eblake: move callbacks to their use point]
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
still, some notes below
---
v3: https://lists.gnu.org/archive/html/qemu-devel/2024-04/msg00375.html
in v4, factor even the struct to the .c files, avoiding a union [Vladimir]
nbd/nbd-internal.h | 10 ----------
nbd/client.c | 27 +++++++++++++++++++++++----
nbd/common.c | 11 -----------
nbd/server.c | 29 +++++++++++++++++++++++------
4 files changed, 46 insertions(+), 31 deletions(-)
diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index dfa02f77ee4..91895106a95 100644
--- a/nbd/nbd-internal.h
+++ b/nbd/nbd-internal.h
@@ -72,16 +72,6 @@ static inline int nbd_write(QIOChannel *ioc, const void
*buffer, size_t size,
return qio_channel_write_all(ioc, buffer, size, errp) < 0 ? -EIO : 0;
}
-struct NBDTLSHandshakeData {
- GMainLoop *loop;
- bool complete;
- Error *error;
-};
-
-
-void nbd_tls_handshake(QIOTask *task,
- void *opaque);
-
int nbd_drop(QIOChannel *ioc, size_t size, Error **errp);
#endif
diff --git a/nbd/client.c b/nbd/client.c
index 29ffc609a4b..c7141d7a098 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -596,13 +596,31 @@ static int nbd_request_simple_option(QIOChannel *ioc, int
opt, bool strict,
return 1;
}
+/* Callback to learn when QIO TLS upgrade is complete */
+struct NBDTLSClientHandshakeData {
+ bool complete;
+ Error *error;
+ GMainLoop *loop;
+};
+
+static void nbd_client_tls_handshake(QIOTask *task, void *opaque)
+{
+ struct NBDTLSClientHandshakeData *data = opaque;
+
+ qio_task_propagate_error(task, &data->error);
+ data->complete = true;
+ if (data->loop) {
+ g_main_loop_quit(data->loop);
+ }
+}
+
static QIOChannel *nbd_receive_starttls(QIOChannel *ioc,
QCryptoTLSCreds *tlscreds,
const char *hostname, Error **errp)
{
int ret;
QIOChannelTLS *tioc;
- struct NBDTLSHandshakeData data = { 0 };
+ struct NBDTLSClientHandshakeData data = { 0 };
ret = nbd_request_simple_option(ioc, NBD_OPT_STARTTLS, true, errp);
if (ret <= 0) {
@@ -619,18 +637,19 @@ static QIOChannel *nbd_receive_starttls(QIOChannel *ioc,
return NULL;
}
qio_channel_set_name(QIO_CHANNEL(tioc), "nbd-client-tls");
- data.loop = g_main_loop_new(g_main_context_default(), FALSE);
trace_nbd_receive_starttls_tls_handshake();
qio_channel_tls_handshake(tioc,
- nbd_tls_handshake,
+ nbd_client_tls_handshake,
&data,
NULL,
NULL);
if (!data.complete) {
+ data.loop = g_main_loop_new(g_main_context_default(), FALSE);
g_main_loop_run(data.loop);
+ g_main_loop_unref(data.loop);
probably good to assert(data.complete);
}
- g_main_loop_unref(data.loop);
+
if (data.error) {
error_propagate(errp, data.error);
object_unref(OBJECT(tioc));
diff --git a/nbd/common.c b/nbd/common.c
index 3247c1d618a..589a748cfe6 100644
--- a/nbd/common.c
+++ b/nbd/common.c
@@ -47,17 +47,6 @@ int nbd_drop(QIOChannel *ioc, size_t size, Error **errp)
}
-void nbd_tls_handshake(QIOTask *task,
- void *opaque)
-{
- struct NBDTLSHandshakeData *data = opaque;
-
- qio_task_propagate_error(task, &data->error);
- data->complete = true;
- g_main_loop_quit(data->loop);
-}
-
-
const char *nbd_opt_lookup(uint32_t opt)
{
switch (opt) {
diff --git a/nbd/server.c b/nbd/server.c
index c3484cc1ebc..ea13cf0e766 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -748,6 +748,23 @@ static int nbd_negotiate_handle_info(NBDClient *client,
Error **errp)
return rc;
}
+/* Callback to learn when QIO TLS upgrade is complete */
+struct NBDTLSServerHandshakeData {
+ bool complete;
+ Error *error;
+ Coroutine *co;
+};
+
+static void nbd_server_tls_handshake(QIOTask *task, void *opaque)
+{
+ struct NBDTLSServerHandshakeData *data = opaque;
+
+ qio_task_propagate_error(task, &data->error);
+ data->complete = true;
+ if (!qemu_coroutine_entered(data->co)) {
+ aio_co_wake(data->co);
+ }
+}
/* Handle NBD_OPT_STARTTLS. Return NULL to drop connection, or else the
* new channel for all further (now-encrypted) communication. */
@@ -756,7 +773,7 @@ static QIOChannel *nbd_negotiate_handle_starttls(NBDClient
*client,
{
QIOChannel *ioc;
QIOChannelTLS *tioc;
- struct NBDTLSHandshakeData data = { 0 };
+ struct NBDTLSServerHandshakeData data = { 0 };
assert(client->opt == NBD_OPT_STARTTLS);
@@ -777,17 +794,17 @@ static QIOChannel
*nbd_negotiate_handle_starttls(NBDClient *client,
preexisting: lack coroutine_fn, as well as caller nbd_negotiate_options()
qio_channel_set_name(QIO_CHANNEL(tioc), "nbd-server-tls");
trace_nbd_negotiate_handle_starttls_handshake();
- data.loop = g_main_loop_new(g_main_context_default(), FALSE);
+ data.co = qemu_coroutine_self();
qio_channel_tls_handshake(tioc,
- nbd_tls_handshake,
+ nbd_server_tls_handshake,
&data,
NULL,
NULL);
- if (!data.complete) {
- g_main_loop_run(data.loop);
+ while (!data.complete) {
not "if", but "while".. Do we expect entering from somewhere except
nbd_server_tls_handshake?
if not, probably safer construction would be
if (!data.complete) {
qemu_coroutine_yield();
assert(data.complete);
}
- to avoid hiding unexpected coroutine switching bugs
+ qemu_coroutine_yield();
}
- g_main_loop_unref(data.loop);
+
if (data.error) {
object_unref(OBJECT(tioc));
error_propagate(errp, data.error);
--
Best regards,
Vladimir