[PATCH v6] Work around vhost-user-blk-test hang

Raphael Norwitz posted 1 patch 1 week, 2 days ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20211014043216.10325-1-raphael.norwitz@nutanix.com
Maintainers: Thomas Huth <thuth@redhat.com>, Laurent Vivier <lvivier@redhat.com>, Coiby Xu <Coiby.Xu@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>
tests/qtest/vhost-user-blk-test.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)

[PATCH v6] Work around vhost-user-blk-test hang

Posted by Raphael Norwitz 1 week, 2 days ago
The vhost-user-blk-test qtest has been hanging intermittently for a
while. The root cause is not yet fully understood, but the hang is
impacting enough users that it is important to merge a workaround for
it.

The race which causes the hang occurs early on in vhost-user setup,
where a vhost-user message is never received by the backend. Forcing
QEMU to wait until the storage-daemon has had some time to initialize
prevents the hang. Thus the existing storage-daemon pidfile option can
be used to implement a workaround cleanly and effectively, since it
creates a file only once the storage-daemon initialization is complete.

This change implements a workaround for the vhost-user-blk-test hang by
making QEMU wait until the storage-daemon has written out a pidfile
before attempting to connect and send messages over the vhost-user
socket.

Some relevent mailing list discussions:

[1] https://lore.kernel.org/qemu-devel/CAFEAcA8kYpz9LiPNxnWJAPSjc=nv532bEdyfynaBeMeohqBp3A@mail.gmail.com/
[2] https://lore.kernel.org/qemu-devel/YWaky%2FKVbS%2FKZjlV@stefanha-x1.localdomain/

Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 tests/qtest/vhost-user-blk-test.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/tests/qtest/vhost-user-blk-test.c b/tests/qtest/vhost-user-blk-test.c
index 6f108a1b62..c6626a286b 100644
--- a/tests/qtest/vhost-user-blk-test.c
+++ b/tests/qtest/vhost-user-blk-test.c
@@ -24,6 +24,7 @@
 #define TEST_IMAGE_SIZE         (64 * 1024 * 1024)
 #define QVIRTIO_BLK_TIMEOUT_US  (30 * 1000 * 1000)
 #define PCI_SLOT_HP             0x06
+#define PIDFILE_RETRIES         5
 
 typedef struct {
     pid_t pid;
@@ -885,7 +886,8 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
                                  int num_queues)
 {
     const char *vhost_user_blk_bin = qtest_qemu_storage_daemon_binary();
-    int i;
+    int i, retries;
+    char *daemon_pidfile_path;
     gchar *img_path;
     GString *storage_daemon_command = g_string_new(NULL);
     QemuStorageDaemonState *qsd;
@@ -898,6 +900,8 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
             " -object memory-backend-memfd,id=mem,size=256M,share=on "
             " -M memory-backend=mem -m 256M ");
 
+    daemon_pidfile_path = g_strdup_printf("/tmp/daemon-%d", getpid());
+
     for (i = 0; i < vus_instances; i++) {
         int fd;
         char *sock_path = create_listen_socket(&fd);
@@ -914,6 +918,9 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
                                i + 1, sock_path);
     }
 
+    g_string_append_printf(storage_daemon_command, "--pidfile %s ",
+                           daemon_pidfile_path);
+
     g_test_message("starting vhost-user backend: %s",
                    storage_daemon_command->str);
     pid_t pid = fork();
@@ -930,7 +937,27 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
         execlp("/bin/sh", "sh", "-c", storage_daemon_command->str, NULL);
         exit(1);
     }
+
+    /*
+     * FIXME: The loop here ensures the storage-daemon has come up properly
+     *        before allowing the test to proceed. This is a workaround for
+     *        a race which used to cause the vhost-user-blk-test to hang. It
+     *        should be deleted once the root cause is fully understood and
+     *        fixed.
+     */
+    retries = 0;
+    while (access(daemon_pidfile_path, F_OK) != 0) {
+        g_assert_cmpint(retries, <, PIDFILE_RETRIES);
+
+        retries++;
+        g_usleep(1000);
+    }
+
     g_string_free(storage_daemon_command, true);
+    if (access(daemon_pidfile_path, F_OK) == 0) {
+        unlink(daemon_pidfile_path);
+    }
+    g_free(daemon_pidfile_path);
 
     qsd = g_new(QemuStorageDaemonState, 1);
     qsd->pid = pid;
-- 
2.20.1

Re: [PATCH v6] Work around vhost-user-blk-test hang

Posted by Michael S. Tsirkin 5 days, 1 hour ago
On Thu, Oct 14, 2021 at 04:32:23AM +0000, Raphael Norwitz wrote:
> The vhost-user-blk-test qtest has been hanging intermittently for a
> while. The root cause is not yet fully understood, but the hang is
> impacting enough users that it is important to merge a workaround for
> it.
> 
> The race which causes the hang occurs early on in vhost-user setup,
> where a vhost-user message is never received by the backend. Forcing
> QEMU to wait until the storage-daemon has had some time to initialize
> prevents the hang. Thus the existing storage-daemon pidfile option can
> be used to implement a workaround cleanly and effectively, since it
> creates a file only once the storage-daemon initialization is complete.
> 
> This change implements a workaround for the vhost-user-blk-test hang by
> making QEMU wait until the storage-daemon has written out a pidfile
> before attempting to connect and send messages over the vhost-user
> socket.
> 
> Some relevent mailing list discussions:
> 
> [1] https://lore.kernel.org/qemu-devel/CAFEAcA8kYpz9LiPNxnWJAPSjc=nv532bEdyfynaBeMeohqBp3A@mail.gmail.com/
> [2] https://lore.kernel.org/qemu-devel/YWaky%2FKVbS%2FKZjlV@stefanha-x1.localdomain/
> 
> Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>


Um. Does not seem to make things better for me:

**
ERROR:../tests/qtest/vhost-user-blk-test.c:950:start_vhost_user_blk: assertion failed (retries < PIDFILE_RETRIES): (5 < 5)
ERROR qtest-x86_64/qos-test - Bail out! ERROR:../tests/qtest/vhost-user-blk-test.c:950:start_vhost_user_blk: assertion failed (retries < PIDFILE_RETRIES): (5 < 5)

At this point I just disabled the test in meson. No need to make
everyone suffer.


> ---
>  tests/qtest/vhost-user-blk-test.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/qtest/vhost-user-blk-test.c b/tests/qtest/vhost-user-blk-test.c
> index 6f108a1b62..c6626a286b 100644
> --- a/tests/qtest/vhost-user-blk-test.c
> +++ b/tests/qtest/vhost-user-blk-test.c
> @@ -24,6 +24,7 @@
>  #define TEST_IMAGE_SIZE         (64 * 1024 * 1024)
>  #define QVIRTIO_BLK_TIMEOUT_US  (30 * 1000 * 1000)
>  #define PCI_SLOT_HP             0x06
> +#define PIDFILE_RETRIES         5
>  
>  typedef struct {
>      pid_t pid;


Don't like the arbitrary retries counter.

Let's warn maybe, but on a busy machine we might not complete this
in time ...


> @@ -885,7 +886,8 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
>                                   int num_queues)
>  {
>      const char *vhost_user_blk_bin = qtest_qemu_storage_daemon_binary();
> -    int i;
> +    int i, retries;
> +    char *daemon_pidfile_path;
>      gchar *img_path;
>      GString *storage_daemon_command = g_string_new(NULL);
>      QemuStorageDaemonState *qsd;
> @@ -898,6 +900,8 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
>              " -object memory-backend-memfd,id=mem,size=256M,share=on "
>              " -M memory-backend=mem -m 256M ");
>  
> +    daemon_pidfile_path = g_strdup_printf("/tmp/daemon-%d", getpid());
> +

Ugh. Predictable paths directly in /tmp are problematic .. mktemp?

>      for (i = 0; i < vus_instances; i++) {
>          int fd;
>          char *sock_path = create_listen_socket(&fd);
> @@ -914,6 +918,9 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
>                                 i + 1, sock_path);
>      }
>  
> +    g_string_append_printf(storage_daemon_command, "--pidfile %s ",
> +                           daemon_pidfile_path);
> +
>      g_test_message("starting vhost-user backend: %s",
>                     storage_daemon_command->str);
>      pid_t pid = fork();
> @@ -930,7 +937,27 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
>          execlp("/bin/sh", "sh", "-c", storage_daemon_command->str, NULL);
>          exit(1);
>      }
> +
> +    /*
> +     * FIXME: The loop here ensures the storage-daemon has come up properly
> +     *        before allowing the test to proceed. This is a workaround for
> +     *        a race which used to cause the vhost-user-blk-test to hang. It
> +     *        should be deleted once the root cause is fully understood and
> +     *        fixed.
> +     */
> +    retries = 0;
> +    while (access(daemon_pidfile_path, F_OK) != 0) {
> +        g_assert_cmpint(retries, <, PIDFILE_RETRIES);
> +
> +        retries++;
> +        g_usleep(1000);
> +    }
> +
>      g_string_free(storage_daemon_command, true);
> +    if (access(daemon_pidfile_path, F_OK) == 0) {
> +        unlink(daemon_pidfile_path);
> +    }
> +    g_free(daemon_pidfile_path);
>  
>      qsd = g_new(QemuStorageDaemonState, 1);
>      qsd->pid = pid;
> -- 
> 2.20.1


Re: [PATCH v6] Work around vhost-user-blk-test hang

Posted by Raphael Norwitz 5 days, 1 hour ago
On Mon, Oct 18, 2021 at 05:50:41PM -0400, Michael S. Tsirkin wrote:
> On Thu, Oct 14, 2021 at 04:32:23AM +0000, Raphael Norwitz wrote:
> > The vhost-user-blk-test qtest has been hanging intermittently for a
> > while. The root cause is not yet fully understood, but the hang is
> > impacting enough users that it is important to merge a workaround for
> > it.
> > 
> > The race which causes the hang occurs early on in vhost-user setup,
> > where a vhost-user message is never received by the backend. Forcing
> > QEMU to wait until the storage-daemon has had some time to initialize
> > prevents the hang. Thus the existing storage-daemon pidfile option can
> > be used to implement a workaround cleanly and effectively, since it
> > creates a file only once the storage-daemon initialization is complete.
> > 
> > This change implements a workaround for the vhost-user-blk-test hang by
> > making QEMU wait until the storage-daemon has written out a pidfile
> > before attempting to connect and send messages over the vhost-user
> > socket.
> > 
> > Some relevent mailing list discussions:
> > 
> > [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_qemu-2Ddevel_CAFEAcA8kYpz9LiPNxnWJAPSjc-3Dnv532bEdyfynaBeMeohqBp3A-40mail.gmail.com_&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=In4gmR1pGzKB8G5p6LUrWqkSMec2L5EtXZow_FZNJZk&m=eDRDFhe3H61BSSpDvy3PKzwQIa2grX5hNMhigtjMCJ8&s=c6OKIl0NMsDqP0-ZNnVjHhDq2psXIVszz-uBKw_8pEo&e= 
> > [2] https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_qemu-2Ddevel_YWaky-252FKVbS-252FKZjlV-40stefanha-2Dx1.localdomain_&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=In4gmR1pGzKB8G5p6LUrWqkSMec2L5EtXZow_FZNJZk&m=eDRDFhe3H61BSSpDvy3PKzwQIa2grX5hNMhigtjMCJ8&s=B4EM_0f7TXqsh18YEKOg-cFHabUjsVA5Ie1riDXaB7A&e= 
> > 
> > Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> > Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> 
> Um. Does not seem to make things better for me:
> 
> **
> ERROR:../tests/qtest/vhost-user-blk-test.c:950:start_vhost_user_blk: assertion failed (retries < PIDFILE_RETRIES): (5 < 5)
> ERROR qtest-x86_64/qos-test - Bail out! ERROR:../tests/qtest/vhost-user-blk-test.c:950:start_vhost_user_blk: assertion failed (retries < PIDFILE_RETRIES): (5 < 5)
> 
> At this point I just disabled the test in meson. No need to make
> everyone suffer.

Makes sense. Do you still want to persue the workaround?

If so, can you share some details on how you're running the test?

I've gone through 1000+ iterations using the script I posted here:
https://lore.kernel.org/qemu-devel/20210827165253.GA14291@raphael-debian-dev/
without hitting a failure.

>
> 
> > ---
> >  tests/qtest/vhost-user-blk-test.c | 29 ++++++++++++++++++++++++++++-
> >  1 file changed, 28 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tests/qtest/vhost-user-blk-test.c b/tests/qtest/vhost-user-blk-test.c
> > index 6f108a1b62..c6626a286b 100644
> > --- a/tests/qtest/vhost-user-blk-test.c
> > +++ b/tests/qtest/vhost-user-blk-test.c
> > @@ -24,6 +24,7 @@
> >  #define TEST_IMAGE_SIZE         (64 * 1024 * 1024)
> >  #define QVIRTIO_BLK_TIMEOUT_US  (30 * 1000 * 1000)
> >  #define PCI_SLOT_HP             0x06
> > +#define PIDFILE_RETRIES         5
> >  
> >  typedef struct {
> >      pid_t pid;
> 
> 
> Don't like the arbitrary retries counter.
> 
> Let's warn maybe, but on a busy machine we might not complete this
> in time ...

So you would like it to warn and keep trying forever? Or would you
rather set a much more lenient deadline? (1 min? 5 min?)

> 
> 
> > @@ -885,7 +886,8 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
> >                                   int num_queues)
> >  {
> >      const char *vhost_user_blk_bin = qtest_qemu_storage_daemon_binary();
> > -    int i;
> > +    int i, retries;
> > +    char *daemon_pidfile_path;
> >      gchar *img_path;
> >      GString *storage_daemon_command = g_string_new(NULL);
> >      QemuStorageDaemonState *qsd;
> > @@ -898,6 +900,8 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
> >              " -object memory-backend-memfd,id=mem,size=256M,share=on "
> >              " -M memory-backend=mem -m 256M ");
> >  
> > +    daemon_pidfile_path = g_strdup_printf("/tmp/daemon-%d", getpid());
> > +
> 
> Ugh. Predictable paths directly in /tmp are problematic .. mktemp?
> 

Ack

> >      for (i = 0; i < vus_instances; i++) {
> >          int fd;
> >          char *sock_path = create_listen_socket(&fd);
> > @@ -914,6 +918,9 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
> >                                 i + 1, sock_path);
> >      }
> >  
> > +    g_string_append_printf(storage_daemon_command, "--pidfile %s ",
> > +                           daemon_pidfile_path);
> > +
> >      g_test_message("starting vhost-user backend: %s",
> >                     storage_daemon_command->str);
> >      pid_t pid = fork();
> > @@ -930,7 +937,27 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
> >          execlp("/bin/sh", "sh", "-c", storage_daemon_command->str, NULL);
> >          exit(1);
> >      }
> > +
> > +    /*
> > +     * FIXME: The loop here ensures the storage-daemon has come up properly
> > +     *        before allowing the test to proceed. This is a workaround for
> > +     *        a race which used to cause the vhost-user-blk-test to hang. It
> > +     *        should be deleted once the root cause is fully understood and
> > +     *        fixed.
> > +     */
> > +    retries = 0;
> > +    while (access(daemon_pidfile_path, F_OK) != 0) {
> > +        g_assert_cmpint(retries, <, PIDFILE_RETRIES);
> > +
> > +        retries++;
> > +        g_usleep(1000);
> > +    }
> > +
> >      g_string_free(storage_daemon_command, true);
> > +    if (access(daemon_pidfile_path, F_OK) == 0) {
> > +        unlink(daemon_pidfile_path);
> > +    }
> > +    g_free(daemon_pidfile_path);
> >  
> >      qsd = g_new(QemuStorageDaemonState, 1);
> >      qsd->pid = pid;
> > -- 
> > 2.20.1
> 

Re: [PATCH v6] Work around vhost-user-blk-test hang

Posted by Michael S. Tsirkin 4 days, 17 hours ago
On Mon, Oct 18, 2021 at 10:33:02PM +0000, Raphael Norwitz wrote:
> On Mon, Oct 18, 2021 at 05:50:41PM -0400, Michael S. Tsirkin wrote:
> > On Thu, Oct 14, 2021 at 04:32:23AM +0000, Raphael Norwitz wrote:
> > > The vhost-user-blk-test qtest has been hanging intermittently for a
> > > while. The root cause is not yet fully understood, but the hang is
> > > impacting enough users that it is important to merge a workaround for
> > > it.
> > > 
> > > The race which causes the hang occurs early on in vhost-user setup,
> > > where a vhost-user message is never received by the backend. Forcing
> > > QEMU to wait until the storage-daemon has had some time to initialize
> > > prevents the hang. Thus the existing storage-daemon pidfile option can
> > > be used to implement a workaround cleanly and effectively, since it
> > > creates a file only once the storage-daemon initialization is complete.
> > > 
> > > This change implements a workaround for the vhost-user-blk-test hang by
> > > making QEMU wait until the storage-daemon has written out a pidfile
> > > before attempting to connect and send messages over the vhost-user
> > > socket.
> > > 
> > > Some relevent mailing list discussions:
> > > 
> > > [1] https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_qemu-2Ddevel_CAFEAcA8kYpz9LiPNxnWJAPSjc-3Dnv532bEdyfynaBeMeohqBp3A-40mail.gmail.com_&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=In4gmR1pGzKB8G5p6LUrWqkSMec2L5EtXZow_FZNJZk&m=eDRDFhe3H61BSSpDvy3PKzwQIa2grX5hNMhigtjMCJ8&s=c6OKIl0NMsDqP0-ZNnVjHhDq2psXIVszz-uBKw_8pEo&e= 
> > > [2] https://urldefense.proofpoint.com/v2/url?u=https-3A__lore.kernel.org_qemu-2Ddevel_YWaky-252FKVbS-252FKZjlV-40stefanha-2Dx1.localdomain_&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=In4gmR1pGzKB8G5p6LUrWqkSMec2L5EtXZow_FZNJZk&m=eDRDFhe3H61BSSpDvy3PKzwQIa2grX5hNMhigtjMCJ8&s=B4EM_0f7TXqsh18YEKOg-cFHabUjsVA5Ie1riDXaB7A&e= 
> > > 
> > > Signed-off-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> > > Reviewed-by: Eric Blake <eblake@redhat.com>
> > 
> > 
> > Um. Does not seem to make things better for me:
> > 
> > **
> > ERROR:../tests/qtest/vhost-user-blk-test.c:950:start_vhost_user_blk: assertion failed (retries < PIDFILE_RETRIES): (5 < 5)
> > ERROR qtest-x86_64/qos-test - Bail out! ERROR:../tests/qtest/vhost-user-blk-test.c:950:start_vhost_user_blk: assertion failed (retries < PIDFILE_RETRIES): (5 < 5)
> > 
> > At this point I just disabled the test in meson. No need to make
> > everyone suffer.
> 
> Makes sense. Do you still want to persue the workaround?
> 
> If so, can you share some details on how you're running the test?
> 
> I've gone through 1000+ iterations using the script I posted here:
> https://lore.kernel.org/qemu-devel/20210827165253.GA14291@raphael-debian-dev/
> without hitting a failure.

Hmm my box was busy... now that it's idle I can't repro the failure.



> >
> > 
> > > ---
> > >  tests/qtest/vhost-user-blk-test.c | 29 ++++++++++++++++++++++++++++-
> > >  1 file changed, 28 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/tests/qtest/vhost-user-blk-test.c b/tests/qtest/vhost-user-blk-test.c
> > > index 6f108a1b62..c6626a286b 100644
> > > --- a/tests/qtest/vhost-user-blk-test.c
> > > +++ b/tests/qtest/vhost-user-blk-test.c
> > > @@ -24,6 +24,7 @@
> > >  #define TEST_IMAGE_SIZE         (64 * 1024 * 1024)
> > >  #define QVIRTIO_BLK_TIMEOUT_US  (30 * 1000 * 1000)
> > >  #define PCI_SLOT_HP             0x06
> > > +#define PIDFILE_RETRIES         5
> > >  
> > >  typedef struct {
> > >      pid_t pid;
> > 
> > 
> > Don't like the arbitrary retries counter.
> > 
> > Let's warn maybe, but on a busy machine we might not complete this
> > in time ...
> 
> So you would like it to warn and keep trying forever? Or would you
> rather set a much more lenient deadline? (1 min? 5 min?)

I'm not entirely sure ... Maybe 1 min is enough.
But we want to check that daemon is alive.
And maybe print something about still waiting for it to come up
every X seconds?

> > 
> > 
> > > @@ -885,7 +886,8 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
> > >                                   int num_queues)
> > >  {
> > >      const char *vhost_user_blk_bin = qtest_qemu_storage_daemon_binary();
> > > -    int i;
> > > +    int i, retries;
> > > +    char *daemon_pidfile_path;
> > >      gchar *img_path;
> > >      GString *storage_daemon_command = g_string_new(NULL);
> > >      QemuStorageDaemonState *qsd;
> > > @@ -898,6 +900,8 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
> > >              " -object memory-backend-memfd,id=mem,size=256M,share=on "
> > >              " -M memory-backend=mem -m 256M ");
> > >  
> > > +    daemon_pidfile_path = g_strdup_printf("/tmp/daemon-%d", getpid());
> > > +
> > 
> > Ugh. Predictable paths directly in /tmp are problematic .. mktemp?
> > 
> 
> Ack
> 
> > >      for (i = 0; i < vus_instances; i++) {
> > >          int fd;
> > >          char *sock_path = create_listen_socket(&fd);
> > > @@ -914,6 +918,9 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
> > >                                 i + 1, sock_path);
> > >      }
> > >  
> > > +    g_string_append_printf(storage_daemon_command, "--pidfile %s ",
> > > +                           daemon_pidfile_path);
> > > +
> > >      g_test_message("starting vhost-user backend: %s",
> > >                     storage_daemon_command->str);
> > >      pid_t pid = fork();
> > > @@ -930,7 +937,27 @@ static void start_vhost_user_blk(GString *cmd_line, int vus_instances,
> > >          execlp("/bin/sh", "sh", "-c", storage_daemon_command->str, NULL);
> > >          exit(1);
> > >      }
> > > +
> > > +    /*
> > > +     * FIXME: The loop here ensures the storage-daemon has come up properly
> > > +     *        before allowing the test to proceed. This is a workaround for
> > > +     *        a race which used to cause the vhost-user-blk-test to hang. It
> > > +     *        should be deleted once the root cause is fully understood and
> > > +     *        fixed.
> > > +     */
> > > +    retries = 0;
> > > +    while (access(daemon_pidfile_path, F_OK) != 0) {
> > > +        g_assert_cmpint(retries, <, PIDFILE_RETRIES);
> > > +
> > > +        retries++;
> > > +        g_usleep(1000);
> > > +    }
> > > +
> > >      g_string_free(storage_daemon_command, true);
> > > +    if (access(daemon_pidfile_path, F_OK) == 0) {
> > > +        unlink(daemon_pidfile_path);
> > > +    }
> > > +    g_free(daemon_pidfile_path);
> > >  
> > >      qsd = g_new(QemuStorageDaemonState, 1);
> > >      qsd->pid = pid;
> > > -- 
> > > 2.20.1
> >