1. Patchew
  2. QEMU
  3. [Qemu-devel] [PATCH v4 0/4] monitor: let Monitor be thread safe
  4. View patch

[Qemu-devel] [PATCH v4 2/4] monitor: protect mon->fds with mon_lock

Peter Xu posted 4 patches 7 years, 6 months ago
There is a newer version of this series
[Qemu-devel] [PATCH v4 2/4] monitor: protect mon->fds with mon_lock
Posted by Peter Xu 7 years, 6 months ago 
mon->fds were protected by BQL.  Now protect it by mon_lock so that it
can even be used in monitor iothread.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 monitor.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/monitor.c b/monitor.c
index 48882d28ae..9f361ec21e 100644
--- a/monitor.c
+++ b/monitor.c
@@ -213,7 +213,6 @@ struct Monitor {
     BlockCompletionFunc *password_completion_cb;
     void *password_opaque;
     mon_cmd_t *cmd_table;
-    QLIST_HEAD(,mon_fd_t) fds;
     QTAILQ_ENTRY(Monitor) entry;
 
     /*
@@ -225,6 +224,7 @@ struct Monitor {
     /*
      * Fields that are protected by the per-monitor lock.
      */
+    QLIST_HEAD(, mon_fd_t) fds;
     QString *outbuf;
     guint out_watch;
     /* Read under either BQL or mon_lock, written with BQL+mon_lock.  */
@@ -2207,6 +2207,7 @@ void qmp_getfd(const char *fdname, Error **errp)
         return;
     }
 
+    qemu_mutex_lock(&cur_mon->mon_lock);
     QLIST_FOREACH(monfd, &cur_mon->fds, next) {
         if (strcmp(monfd->name, fdname) != 0) {
             continue;
@@ -2214,6 +2215,7 @@ void qmp_getfd(const char *fdname, Error **errp)
 
         close(monfd->fd);
         monfd->fd = fd;
+        qemu_mutex_unlock(&cur_mon->mon_lock);
         return;
     }
 
@@ -2222,12 +2224,14 @@ void qmp_getfd(const char *fdname, Error **errp)
     monfd->fd = fd;
 
     QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
+    qemu_mutex_unlock(&cur_mon->mon_lock);
 }
 
 void qmp_closefd(const char *fdname, Error **errp)
 {
     mon_fd_t *monfd;
 
+    qemu_mutex_lock(&cur_mon->mon_lock);
     QLIST_FOREACH(monfd, &cur_mon->fds, next) {
         if (strcmp(monfd->name, fdname) != 0) {
             continue;
@@ -2237,9 +2241,11 @@ void qmp_closefd(const char *fdname, Error **errp)
         close(monfd->fd);
         g_free(monfd->name);
         g_free(monfd);
+        qemu_mutex_unlock(&cur_mon->mon_lock);
         return;
     }
 
+    qemu_mutex_unlock(&cur_mon->mon_lock);
     error_setg(errp, QERR_FD_NOT_FOUND, fdname);
 }
 
@@ -2247,6 +2253,7 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
 {
     mon_fd_t *monfd;
 
+    qemu_mutex_lock(&mon->mon_lock);
     QLIST_FOREACH(monfd, &mon->fds, next) {
         int fd;
 
@@ -2260,10 +2267,12 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
         QLIST_REMOVE(monfd, next);
         g_free(monfd->name);
         g_free(monfd);
+        qemu_mutex_unlock(&mon->mon_lock);
 
         return fd;
     }
 
+    qemu_mutex_unlock(&mon->mon_lock);
     error_setg(errp, "File descriptor named '%s' has not been found", fdname);
     return -1;
 }
-- 
2.14.3
Re: [Qemu-devel] [PATCH v4 2/4] monitor: protect mon->fds with mon_lock
Posted by Dr. David Alan Gilbert 7 years, 6 months ago 
* Peter Xu (peterx@redhat.com) wrote:
> mon->fds were protected by BQL.  Now protect it by mon_lock so that it
> can even be used in monitor iothread.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  monitor.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/monitor.c b/monitor.c
> index 48882d28ae..9f361ec21e 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -213,7 +213,6 @@ struct Monitor {
>      BlockCompletionFunc *password_completion_cb;
>      void *password_opaque;
>      mon_cmd_t *cmd_table;
> -    QLIST_HEAD(,mon_fd_t) fds;
>      QTAILQ_ENTRY(Monitor) entry;
>  
>      /*
> @@ -225,6 +224,7 @@ struct Monitor {
>      /*
>       * Fields that are protected by the per-monitor lock.
>       */
> +    QLIST_HEAD(, mon_fd_t) fds;
>      QString *outbuf;
>      guint out_watch;
>      /* Read under either BQL or mon_lock, written with BQL+mon_lock.  */
> @@ -2207,6 +2207,7 @@ void qmp_getfd(const char *fdname, Error **errp)
>          return;
>      }
>  
> +    qemu_mutex_lock(&cur_mon->mon_lock);
>      QLIST_FOREACH(monfd, &cur_mon->fds, next) {
>          if (strcmp(monfd->name, fdname) != 0) {
>              continue;
> @@ -2214,6 +2215,7 @@ void qmp_getfd(const char *fdname, Error **errp)
>  
>          close(monfd->fd);
>          monfd->fd = fd;
> +        qemu_mutex_unlock(&cur_mon->mon_lock);

Why is it safe to have a close() in a mon_lock'd region?
We've got to make sure everything that happens in it is non-blocking.

Dave

>          return;
>      }
>  
> @@ -2222,12 +2224,14 @@ void qmp_getfd(const char *fdname, Error **errp)
>      monfd->fd = fd;
>  
>      QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
> +    qemu_mutex_unlock(&cur_mon->mon_lock);
>  }
>  
>  void qmp_closefd(const char *fdname, Error **errp)
>  {
>      mon_fd_t *monfd;
>  
> +    qemu_mutex_lock(&cur_mon->mon_lock);
>      QLIST_FOREACH(monfd, &cur_mon->fds, next) {
>          if (strcmp(monfd->name, fdname) != 0) {
>              continue;
> @@ -2237,9 +2241,11 @@ void qmp_closefd(const char *fdname, Error **errp)
>          close(monfd->fd);
>          g_free(monfd->name);
>          g_free(monfd);
> +        qemu_mutex_unlock(&cur_mon->mon_lock);
>          return;
>      }
>  
> +    qemu_mutex_unlock(&cur_mon->mon_lock);
>      error_setg(errp, QERR_FD_NOT_FOUND, fdname);
>  }
>  
> @@ -2247,6 +2253,7 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
>  {
>      mon_fd_t *monfd;
>  
> +    qemu_mutex_lock(&mon->mon_lock);
>      QLIST_FOREACH(monfd, &mon->fds, next) {
>          int fd;
>  
> @@ -2260,10 +2267,12 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
>          QLIST_REMOVE(monfd, next);
>          g_free(monfd->name);
>          g_free(monfd);
> +        qemu_mutex_unlock(&mon->mon_lock);
>  
>          return fd;
>      }
>  
> +    qemu_mutex_unlock(&mon->mon_lock);
>      error_setg(errp, "File descriptor named '%s' has not been found", fdname);
>      return -1;
>  }
> -- 
> 2.14.3
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
Re: [Qemu-devel] [PATCH v4 2/4] monitor: protect mon->fds with mon_lock
Posted by Peter Xu 7 years, 6 months ago 
On Wed, May 02, 2018 at 12:15:07PM +0100, Dr. David Alan Gilbert wrote:
> * Peter Xu (peterx@redhat.com) wrote:
> > mon->fds were protected by BQL.  Now protect it by mon_lock so that it
> > can even be used in monitor iothread.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  monitor.c | 11 ++++++++++-
> >  1 file changed, 10 insertions(+), 1 deletion(-)
> > 
> > diff --git a/monitor.c b/monitor.c
> > index 48882d28ae..9f361ec21e 100644
> > --- a/monitor.c
> > +++ b/monitor.c
> > @@ -213,7 +213,6 @@ struct Monitor {
> >      BlockCompletionFunc *password_completion_cb;
> >      void *password_opaque;
> >      mon_cmd_t *cmd_table;
> > -    QLIST_HEAD(,mon_fd_t) fds;
> >      QTAILQ_ENTRY(Monitor) entry;
> >  
> >      /*
> > @@ -225,6 +224,7 @@ struct Monitor {
> >      /*
> >       * Fields that are protected by the per-monitor lock.
> >       */
> > +    QLIST_HEAD(, mon_fd_t) fds;
> >      QString *outbuf;
> >      guint out_watch;
> >      /* Read under either BQL or mon_lock, written with BQL+mon_lock.  */
> > @@ -2207,6 +2207,7 @@ void qmp_getfd(const char *fdname, Error **errp)
> >          return;
> >      }
> >  
> > +    qemu_mutex_lock(&cur_mon->mon_lock);
> >      QLIST_FOREACH(monfd, &cur_mon->fds, next) {
> >          if (strcmp(monfd->name, fdname) != 0) {
> >              continue;
> > @@ -2214,6 +2215,7 @@ void qmp_getfd(const char *fdname, Error **errp)
> >  
> >          close(monfd->fd);
> >          monfd->fd = fd;
> > +        qemu_mutex_unlock(&cur_mon->mon_lock);
> 
> Why is it safe to have a close() in a mon_lock'd region?
> We've got to make sure everything that happens in it is non-blocking.

Hmm indeed.  Let me move that close() out of the critical section. I
think I need to touch up below [1] too since it'll has similar
problem.

I'll wait for some more comments to repost.  Thanks,

> 
> Dave
> 
> >          return;
> >      }
> >  
> > @@ -2222,12 +2224,14 @@ void qmp_getfd(const char *fdname, Error **errp)
> >      monfd->fd = fd;
> >  
> >      QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
> > +    qemu_mutex_unlock(&cur_mon->mon_lock);
> >  }
> >  
> >  void qmp_closefd(const char *fdname, Error **errp)
> >  {
> >      mon_fd_t *monfd;
> >  
> > +    qemu_mutex_lock(&cur_mon->mon_lock);
> >      QLIST_FOREACH(monfd, &cur_mon->fds, next) {
> >          if (strcmp(monfd->name, fdname) != 0) {
> >              continue;
> > @@ -2237,9 +2241,11 @@ void qmp_closefd(const char *fdname, Error **errp)
> >          close(monfd->fd);
> >          g_free(monfd->name);
> >          g_free(monfd);
> > +        qemu_mutex_unlock(&cur_mon->mon_lock);

[1]

> >          return;
> >      }
> >  
> > +    qemu_mutex_unlock(&cur_mon->mon_lock);
> >      error_setg(errp, QERR_FD_NOT_FOUND, fdname);
> >  }
> >  
> > @@ -2247,6 +2253,7 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
> >  {
> >      mon_fd_t *monfd;
> >  
> > +    qemu_mutex_lock(&mon->mon_lock);
> >      QLIST_FOREACH(monfd, &mon->fds, next) {
> >          int fd;
> >  
> > @@ -2260,10 +2267,12 @@ int monitor_get_fd(Monitor *mon, const char *fdname, Error **errp)
> >          QLIST_REMOVE(monfd, next);
> >          g_free(monfd->name);
> >          g_free(monfd);
> > +        qemu_mutex_unlock(&mon->mon_lock);
> >  
> >          return fd;
> >      }
> >  
> > +    qemu_mutex_unlock(&mon->mon_lock);
> >      error_setg(errp, "File descriptor named '%s' has not been found", fdname);
> >      return -1;
> >  }
> > -- 
> > 2.14.3
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

-- 
Peter Xu

Patchew 2.1-devel-b67e4c2

© 2016 - 2025 Red Hat, Inc.