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[PATCH v3 0/3] xen: optimize xenbus performance

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  [PATCH v3 0/3] xen: optimize xenbus performance Juergen Gross <jgross@suse.com> - 2017-01-23 11:10 +0100
    [PATCH v3 2/3] xen: modify xenstore watch event interface Juergen Gross <jgross@suse.com> - 2017-01-23 11:10 +0100
    [PATCH v3 1/3] xen: clean up xenbus internal headers Juergen Gross <jgross@suse.com> - 2017-01-23 11:20 +0100
    Re: [PATCH v3 3/3] xen: optimize xenbus driver for multiple  concurrent xenstore accesses Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2017-01-23 20:00 +0100
      Re: [PATCH v3 3/3] xen: optimize xenbus driver for multiple  concurrent xenstore accesses Boris Ostrovsky <boris.ostrovsky@oracle.com> - 2017-01-24 14:50 +0100
        Re: [PATCH v3 3/3] xen: optimize xenbus driver for multiple  concurrent xenstore accesses Juergen Gross <jgross@suse.com> - 2017-01-24 17:30 +0100

#1564838 — [PATCH v3 0/3] xen: optimize xenbus performance

The xenbus driver used for communication with Xenstore (all kernel
accesses to Xenstore and in case of Xenstore living in another domain
all accesses of the local domain to Xenstore) is rather simple
especially regarding multiple concurrent accesses: they are just being
serialized in spite of Xenstore being capable to handle multiple
parallel accesses.

Clean up the external interface(s) of xenbus and optimize its
performance by allowing multiple concurrent accesses to Xenstore.

V3:
- patch 3: simplify coding as requested by Boris Ostrovsky

V2:
- patch 1: update commit message, re-add lost copyright
- patch 3: address comments of Boris Ostrovsky:
    - guard xs_request_id by lock
    - move state struct definitions to the place where they are being
      used
    - rate limit some warnings
    - use barrier() instead of cpu_relax()
    - add/remove some comments
    - minor changes like naming of variables

Juergen Gross (3):
  xen: clean up xenbus internal headers
  xen: modify xenstore watch event interface
  xen: optimize xenbus driver for multiple concurrent xenstore accesses

 drivers/block/xen-blkback/xenbus.c         |   6 +-
 drivers/net/xen-netback/xenbus.c           |   8 +-
 drivers/xen/cpu_hotplug.c                  |   5 +-
 drivers/xen/manage.c                       |   6 +-
 drivers/xen/xen-balloon.c                  |   2 +-
 drivers/xen/xen-pciback/xenbus.c           |   2 +-
 drivers/xen/xenbus/xenbus.h                | 135 +++++++
 drivers/xen/xenbus/xenbus_client.c         |   6 +-
 drivers/xen/xenbus/xenbus_comms.c          | 315 +++++++++++++++--
 drivers/xen/xenbus/xenbus_comms.h          |  51 ---
 drivers/xen/xenbus/xenbus_dev_backend.c    |   2 +-
 drivers/xen/xenbus/xenbus_dev_frontend.c   | 213 ++++++-----
 drivers/xen/xenbus/xenbus_probe.c          |  14 +-
 drivers/xen/xenbus/xenbus_probe.h          |  88 -----
 drivers/xen/xenbus/xenbus_probe_backend.c  |  11 +-
 drivers/xen/xenbus/xenbus_probe_frontend.c |  17 +-
 drivers/xen/xenbus/xenbus_xs.c             | 544 +++++++++++++----------------
 drivers/xen/xenfs/super.c                  |   2 +-
 drivers/xen/xenfs/xenstored.c              |   2 +-
 include/xen/xenbus.h                       |  18 +-
 20 files changed, 835 insertions(+), 612 deletions(-)
 create mode 100644 drivers/xen/xenbus/xenbus.h
 delete mode 100644 drivers/xen/xenbus/xenbus_comms.h
 delete mode 100644 drivers/xen/xenbus/xenbus_probe.h

Cc: konrad.wilk@oracle.com
Cc: roger.pau@citrix.com
Cc: wei.liu2@citrix.com
Cc: paul.durrant@citrix.com
Cc: netdev@vger.kernel.org
-- 
2.10.2

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#1564842 — [PATCH v3 2/3] xen: modify xenstore watch event interface

Today a Xenstore watch event is delivered via a callback function
declared as:

void (*callback)(struct xenbus_watch *,
                 const char **vec, unsigned int len);

As all watch events only ever come with two parameters (path and token)
changing the prototype to:

void (*callback)(struct xenbus_watch *,
                 const char *path, const char *token);

is the natural thing to do.

Apply this change and adapt all users.

Cc: konrad.wilk@oracle.com
Cc: roger.pau@citrix.com
Cc: wei.liu2@citrix.com
Cc: paul.durrant@citrix.com
Cc: netdev@vger.kernel.org

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 drivers/block/xen-blkback/xenbus.c         |  6 +++---
 drivers/net/xen-netback/xenbus.c           |  8 ++++----
 drivers/xen/cpu_hotplug.c                  |  5 ++---
 drivers/xen/manage.c                       |  6 +++---
 drivers/xen/xen-balloon.c                  |  2 +-
 drivers/xen/xen-pciback/xenbus.c           |  2 +-
 drivers/xen/xenbus/xenbus.h                |  6 +++---
 drivers/xen/xenbus/xenbus_client.c         |  4 ++--
 drivers/xen/xenbus/xenbus_dev_frontend.c   | 21 ++++++++-------------
 drivers/xen/xenbus/xenbus_probe.c          | 11 ++++-------
 drivers/xen/xenbus/xenbus_probe_backend.c  |  8 ++++----
 drivers/xen/xenbus/xenbus_probe_frontend.c | 14 +++++++-------
 drivers/xen/xenbus/xenbus_xs.c             | 29 ++++++++++++++---------------
 include/xen/xenbus.h                       |  6 +++---
 14 files changed, 59 insertions(+), 69 deletions(-)

diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 415e79b..8fe61b5 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -38,8 +38,8 @@ struct backend_info {
 static struct kmem_cache *xen_blkif_cachep;
 static void connect(struct backend_info *);
 static int connect_ring(struct backend_info *);
-static void backend_changed(struct xenbus_watch *, const char **,
-			    unsigned int);
+static void backend_changed(struct xenbus_watch *, const char *,
+			    const char *);
 static void xen_blkif_free(struct xen_blkif *blkif);
 static void xen_vbd_free(struct xen_vbd *vbd);
 
@@ -661,7 +661,7 @@ static int xen_blkbk_probe(struct xenbus_device *dev,
  * ready, connect.
  */
 static void backend_changed(struct xenbus_watch *watch,
-			    const char **vec, unsigned int len)
+			    const char *path, const char *token)
 {
 	int err;
 	unsigned major;
diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 3124eae..d8a40fa 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -723,7 +723,7 @@ static int xen_net_read_mac(struct xenbus_device *dev, u8 mac[])
 }
 
 static void xen_net_rate_changed(struct xenbus_watch *watch,
-				const char **vec, unsigned int len)
+				 const char *path, const char *token)
 {
 	struct xenvif *vif = container_of(watch, struct xenvif, credit_watch);
 	struct xenbus_device *dev = xenvif_to_xenbus_device(vif);
@@ -780,7 +780,7 @@ static void xen_unregister_credit_watch(struct xenvif *vif)
 }
 
 static void xen_mcast_ctrl_changed(struct xenbus_watch *watch,
-				   const char **vec, unsigned int len)
+				   const char *path, const char *token)
 {
 	struct xenvif *vif = container_of(watch, struct xenvif,
 					  mcast_ctrl_watch);
@@ -855,8 +855,8 @@ static void unregister_hotplug_status_watch(struct backend_info *be)
 }
 
 static void hotplug_status_changed(struct xenbus_watch *watch,
-				   const char **vec,
-				   unsigned int vec_size)
+				   const char *path,
+				   const char *token)
 {
 	struct backend_info *be = container_of(watch,
 					       struct backend_info,
diff --git a/drivers/xen/cpu_hotplug.c b/drivers/xen/cpu_hotplug.c
index 5676aef..7a4daa2 100644
--- a/drivers/xen/cpu_hotplug.c
+++ b/drivers/xen/cpu_hotplug.c
@@ -68,13 +68,12 @@ static void vcpu_hotplug(unsigned int cpu)
 }
 
 static void handle_vcpu_hotplug_event(struct xenbus_watch *watch,
-					const char **vec, unsigned int len)
+				      const char *path, const char *token)
 {
 	unsigned int cpu;
 	char *cpustr;
-	const char *node = vec[XS_WATCH_PATH];
 
-	cpustr = strstr(node, "cpu/");
+	cpustr = strstr(path, "cpu/");
 	if (cpustr != NULL) {
 		sscanf(cpustr, "cpu/%u", &cpu);
 		vcpu_hotplug(cpu);
diff --git a/drivers/xen/manage.c b/drivers/xen/manage.c
index 26e5e85..ca62c09 100644
--- a/drivers/xen/manage.c
+++ b/drivers/xen/manage.c
@@ -218,7 +218,7 @@ static struct shutdown_handler shutdown_handlers[] = {
 };
 
 static void shutdown_handler(struct xenbus_watch *watch,
-			     const char **vec, unsigned int len)
+			     const char *path, const char *token)
 {
 	char *str;
 	struct xenbus_transaction xbt;
@@ -266,8 +266,8 @@ static void shutdown_handler(struct xenbus_watch *watch,
 }
 
 #ifdef CONFIG_MAGIC_SYSRQ
-static void sysrq_handler(struct xenbus_watch *watch, const char **vec,
-			  unsigned int len)
+static void sysrq_handler(struct xenbus_watch *watch, const char *path,
+			  const char *token)
 {
 	char sysrq_key = '\0';
 	struct xenbus_transaction xbt;
diff --git a/drivers/xen/xen-balloon.c b/drivers/xen/xen-balloon.c
index 79865b8..e7715cb 100644
--- a/drivers/xen/xen-balloon.c
+++ b/drivers/xen/xen-balloon.c
@@ -55,7 +55,7 @@ static int register_balloon(struct device *dev);
 
 /* React to a change in the target key */
 static void watch_target(struct xenbus_watch *watch,
-			 const char **vec, unsigned int len)
+			 const char *path, const char *token)
 {
 	unsigned long long new_target;
 	int err;
diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c
index 3f0aee0..3814b44 100644
--- a/drivers/xen/xen-pciback/xenbus.c
+++ b/drivers/xen/xen-pciback/xenbus.c
@@ -652,7 +652,7 @@ static int xen_pcibk_setup_backend(struct xen_pcibk_device *pdev)
 }
 
 static void xen_pcibk_be_watch(struct xenbus_watch *watch,
-			     const char **vec, unsigned int len)
+			       const char *path, const char *token)
 {
 	struct xen_pcibk_device *pdev =
 	    container_of(watch, struct xen_pcibk_device, be_watch);
diff --git a/drivers/xen/xenbus/xenbus.h b/drivers/xen/xenbus/xenbus.h
index a6b007d..5199527 100644
--- a/drivers/xen/xenbus/xenbus.h
+++ b/drivers/xen/xenbus/xenbus.h
@@ -40,8 +40,8 @@ struct xen_bus_type {
 	int (*get_bus_id)(char bus_id[XEN_BUS_ID_SIZE], const char *nodename);
 	int (*probe)(struct xen_bus_type *bus, const char *type,
 		     const char *dir);
-	void (*otherend_changed)(struct xenbus_watch *watch, const char **vec,
-				 unsigned int len);
+	void (*otherend_changed)(struct xenbus_watch *watch, const char *path,
+				 const char *token);
 	struct bus_type bus;
 };
 
@@ -84,7 +84,7 @@ int xenbus_dev_resume(struct device *dev);
 int xenbus_dev_cancel(struct device *dev);
 
 void xenbus_otherend_changed(struct xenbus_watch *watch,
-			     const char **vec, unsigned int len,
+			     const char *path, const char *token,
 			     int ignore_on_shutdown);
 
 int xenbus_read_otherend_details(struct xenbus_device *xendev,
diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
index 23edf53..9586c24 100644
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -115,7 +115,7 @@ EXPORT_SYMBOL_GPL(xenbus_strstate);
 int xenbus_watch_path(struct xenbus_device *dev, const char *path,
 		      struct xenbus_watch *watch,
 		      void (*callback)(struct xenbus_watch *,
-				       const char **, unsigned int))
+				       const char *, const char *))
 {
 	int err;
 
@@ -153,7 +153,7 @@ EXPORT_SYMBOL_GPL(xenbus_watch_path);
 int xenbus_watch_pathfmt(struct xenbus_device *dev,
 			 struct xenbus_watch *watch,
 			 void (*callback)(struct xenbus_watch *,
-					const char **, unsigned int),
+					  const char *, const char *),
 			 const char *pathfmt, ...)
 {
 	int err;
diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index e2bc9b3..e4b9847 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -258,26 +258,23 @@ static struct watch_adapter *alloc_watch_adapter(const char *path,
 }
 
 static void watch_fired(struct xenbus_watch *watch,
-			const char **vec,
-			unsigned int len)
+			const char *path,
+			const char *token)
 {
 	struct watch_adapter *adap;
 	struct xsd_sockmsg hdr;
-	const char *path, *token;
-	int path_len, tok_len, body_len, data_len = 0;
+	const char *token_caller;
+	int path_len, tok_len, body_len;
 	int ret;
 	LIST_HEAD(staging_q);
 
 	adap = container_of(watch, struct watch_adapter, watch);
 
-	path = vec[XS_WATCH_PATH];
-	token = adap->token;
+	token_caller = adap->token;
 
 	path_len = strlen(path) + 1;
-	tok_len = strlen(token) + 1;
-	if (len > 2)
-		data_len = vec[len] - vec[2] + 1;
-	body_len = path_len + tok_len + data_len;
+	tok_len = strlen(token_caller) + 1;
+	body_len = path_len + tok_len;
 
 	hdr.type = XS_WATCH_EVENT;
 	hdr.len = body_len;
@@ -288,9 +285,7 @@ static void watch_fired(struct xenbus_watch *watch,
 	if (!ret)
 		ret = queue_reply(&staging_q, path, path_len);
 	if (!ret)
-		ret = queue_reply(&staging_q, token, tok_len);
-	if (!ret && len > 2)
-		ret = queue_reply(&staging_q, vec[2], data_len);
+		ret = queue_reply(&staging_q, token_caller, tok_len);
 
 	if (!ret) {
 		/* success: pass reply list onto watcher */
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 6baffbb..74888ca 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -169,7 +169,7 @@ int xenbus_read_otherend_details(struct xenbus_device *xendev,
 EXPORT_SYMBOL_GPL(xenbus_read_otherend_details);
 
 void xenbus_otherend_changed(struct xenbus_watch *watch,
-			     const char **vec, unsigned int len,
+			     const char *path, const char *token,
 			     int ignore_on_shutdown)
 {
 	struct xenbus_device *dev =
@@ -180,18 +180,15 @@ void xenbus_otherend_changed(struct xenbus_watch *watch,
 	/* Protect us against watches firing on old details when the otherend
 	   details change, say immediately after a resume. */
 	if (!dev->otherend ||
-	    strncmp(dev->otherend, vec[XS_WATCH_PATH],
-		    strlen(dev->otherend))) {
-		dev_dbg(&dev->dev, "Ignoring watch at %s\n",
-			vec[XS_WATCH_PATH]);
+	    strncmp(dev->otherend, path, strlen(dev->otherend))) {
+		dev_dbg(&dev->dev, "Ignoring watch at %s\n", path);
 		return;
 	}
 
 	state = xenbus_read_driver_state(dev->otherend);
 
 	dev_dbg(&dev->dev, "state is %d, (%s), %s, %s\n",
-		state, xenbus_strstate(state), dev->otherend_watch.node,
-		vec[XS_WATCH_PATH]);
+		state, xenbus_strstate(state), dev->otherend_watch.node, path);
 
 	/*
 	 * Ignore xenbus transitions during shutdown. This prevents us doing
diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
index f46b4dc..b0bed4f 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -181,9 +181,9 @@ static int xenbus_probe_backend(struct xen_bus_type *bus, const char *type,
 }
 
 static void frontend_changed(struct xenbus_watch *watch,
-			    const char **vec, unsigned int len)
+			     const char *path, const char *token)
 {
-	xenbus_otherend_changed(watch, vec, len, 0);
+	xenbus_otherend_changed(watch, path, token, 0);
 }
 
 static struct xen_bus_type xenbus_backend = {
@@ -204,11 +204,11 @@ static struct xen_bus_type xenbus_backend = {
 };
 
 static void backend_changed(struct xenbus_watch *watch,
-			    const char **vec, unsigned int len)
+			    const char *path, const char *token)
 {
 	DPRINTK("");
 
-	xenbus_dev_changed(vec[XS_WATCH_PATH], &xenbus_backend);
+	xenbus_dev_changed(path, &xenbus_backend);
 }
 
 static struct xenbus_watch be_watch = {
diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c b/drivers/xen/xenbus/xenbus_probe_frontend.c
index d7b77a6..19e45ce 100644
--- a/drivers/xen/xenbus/xenbus_probe_frontend.c
+++ b/drivers/xen/xenbus/xenbus_probe_frontend.c
@@ -86,9 +86,9 @@ static int xenbus_uevent_frontend(struct device *_dev,
 
 
 static void backend_changed(struct xenbus_watch *watch,
-			    const char **vec, unsigned int len)
+			    const char *path, const char *token)
 {
-	xenbus_otherend_changed(watch, vec, len, 1);
+	xenbus_otherend_changed(watch, path, token, 1);
 }
 
 static void xenbus_frontend_delayed_resume(struct work_struct *w)
@@ -153,11 +153,11 @@ static struct xen_bus_type xenbus_frontend = {
 };
 
 static void frontend_changed(struct xenbus_watch *watch,
-			     const char **vec, unsigned int len)
+			     const char *path, const char *token)
 {
 	DPRINTK("");
 
-	xenbus_dev_changed(vec[XS_WATCH_PATH], &xenbus_frontend);
+	xenbus_dev_changed(path, &xenbus_frontend);
 }
 
 
@@ -332,13 +332,13 @@ static DECLARE_WAIT_QUEUE_HEAD(backend_state_wq);
 static int backend_state;
 
 static void xenbus_reset_backend_state_changed(struct xenbus_watch *w,
-					const char **v, unsigned int l)
+					const char *path, const char *token)
 {
-	if (xenbus_scanf(XBT_NIL, v[XS_WATCH_PATH], "", "%i",
+	if (xenbus_scanf(XBT_NIL, path, "", "%i",
 			 &backend_state) != 1)
 		backend_state = XenbusStateUnknown;
 	printk(KERN_DEBUG "XENBUS: backend %s %s\n",
-			v[XS_WATCH_PATH], xenbus_strstate(backend_state));
+	       path, xenbus_strstate(backend_state));
 	wake_up(&backend_state_wq);
 }
 
diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index 4c49d87..ebc768f 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -64,8 +64,8 @@ struct xs_stored_msg {
 		/* Queued watch events. */
 		struct {
 			struct xenbus_watch *handle;
-			char **vec;
-			unsigned int vec_size;
+			const char *path;
+			const char *token;
 		} watch;
 	} u;
 };
@@ -765,7 +765,7 @@ void unregister_xenbus_watch(struct xenbus_watch *watch)
 		if (msg->u.watch.handle != watch)
 			continue;
 		list_del(&msg->list);
-		kfree(msg->u.watch.vec);
+		kfree(msg->u.watch.path);
 		kfree(msg);
 	}
 	spin_unlock(&watch_events_lock);
@@ -833,11 +833,10 @@ static int xenwatch_thread(void *unused)
 
 		if (ent != &watch_events) {
 			msg = list_entry(ent, struct xs_stored_msg, list);
-			msg->u.watch.handle->callback(
-				msg->u.watch.handle,
-				(const char **)msg->u.watch.vec,
-				msg->u.watch.vec_size);
-			kfree(msg->u.watch.vec);
+			msg->u.watch.handle->callback(msg->u.watch.handle,
+						      msg->u.watch.path,
+						      msg->u.watch.token);
+			kfree(msg->u.watch.path);
 			kfree(msg);
 		}
 
@@ -903,24 +902,24 @@ static int process_msg(void)
 	body[msg->hdr.len] = '\0';
 
 	if (msg->hdr.type == XS_WATCH_EVENT) {
-		msg->u.watch.vec = split(body, msg->hdr.len,
-					 &msg->u.watch.vec_size);
-		if (IS_ERR(msg->u.watch.vec)) {
-			err = PTR_ERR(msg->u.watch.vec);
+		if (count_strings(body, msg->hdr.len) != 2) {
+			err = -EINVAL;
 			kfree(msg);
+			kfree(body);
 			goto out;
 		}
+		msg->u.watch.path = (const char *)body;
+		msg->u.watch.token = (const char *)strchr(body, '\0') + 1;
 
 		spin_lock(&watches_lock);
-		msg->u.watch.handle = find_watch(
-			msg->u.watch.vec[XS_WATCH_TOKEN]);
+		msg->u.watch.handle = find_watch(msg->u.watch.token);
 		if (msg->u.watch.handle != NULL) {
 			spin_lock(&watch_events_lock);
 			list_add_tail(&msg->list, &watch_events);
 			wake_up(&watch_events_waitq);
 			spin_unlock(&watch_events_lock);
 		} else {
-			kfree(msg->u.watch.vec);
+			kfree(body);
 			kfree(msg);
 		}
 		spin_unlock(&watches_lock);
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 98f73a2..869c816 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -61,7 +61,7 @@ struct xenbus_watch
 
 	/* Callback (executed in a process context with no locks held). */
 	void (*callback)(struct xenbus_watch *,
-			 const char **vec, unsigned int len);
+			 const char *path, const char *token);
 };
 
 
@@ -193,11 +193,11 @@ void xenbus_probe(struct work_struct *);
 int xenbus_watch_path(struct xenbus_device *dev, const char *path,
 		      struct xenbus_watch *watch,
 		      void (*callback)(struct xenbus_watch *,
-				       const char **, unsigned int));
+				       const char *, const char *));
 __printf(4, 5)
 int xenbus_watch_pathfmt(struct xenbus_device *dev, struct xenbus_watch *watch,
 			 void (*callback)(struct xenbus_watch *,
-					  const char **, unsigned int),
+					  const char *, const char *),
 			 const char *pathfmt, ...);
 
 int xenbus_switch_state(struct xenbus_device *dev, enum xenbus_state new_state);
-- 
2.10.2

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#1564844 — [PATCH v3 1/3] xen: clean up xenbus internal headers

The xenbus driver has an awful mixture of internally and globally
visible headers: some of the internally used only stuff is defined in
the global header include/xen/xenbus.h while some stuff defined in
internal headers is used by other drivers, too.

Clean this up by moving the externally used symbols to
include/xen/xenbus.h and the symbols used internally only to a new
header drivers/xen/xenbus/xenbus.h replacing xenbus_comms.h and
xenbus_probe.h

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
v2: update commit message, re-add lost copyright
---
 drivers/xen/xenbus/{xenbus_probe.h => xenbus.h} | 63 ++++++++++++++-----------
 drivers/xen/xenbus/xenbus_client.c              |  2 +-
 drivers/xen/xenbus/xenbus_comms.c               |  2 +-
 drivers/xen/xenbus/xenbus_comms.h               | 51 --------------------
 drivers/xen/xenbus/xenbus_dev_backend.c         |  2 +-
 drivers/xen/xenbus/xenbus_dev_frontend.c        |  4 +-
 drivers/xen/xenbus/xenbus_probe.c               |  3 +-
 drivers/xen/xenbus/xenbus_probe_backend.c       |  3 +-
 drivers/xen/xenbus/xenbus_probe_frontend.c      |  3 +-
 drivers/xen/xenbus/xenbus_xs.c                  |  3 +-
 drivers/xen/xenfs/super.c                       |  2 +-
 drivers/xen/xenfs/xenstored.c                   |  2 +-
 include/xen/xenbus.h                            | 12 ++---
 13 files changed, 52 insertions(+), 100 deletions(-)
 rename drivers/xen/xenbus/{xenbus_probe.h => xenbus.h} (59%)
 delete mode 100644 drivers/xen/xenbus/xenbus_comms.h

diff --git a/drivers/xen/xenbus/xenbus_probe.h b/drivers/xen/xenbus/xenbus.h
similarity index 59%
rename from drivers/xen/xenbus/xenbus_probe.h
rename to drivers/xen/xenbus/xenbus.h
index c9ec7ca..a6b007d 100644
--- a/drivers/xen/xenbus/xenbus_probe.h
+++ b/drivers/xen/xenbus/xenbus.h
@@ -1,7 +1,5 @@
-/******************************************************************************
- * xenbus_probe.h
- *
- * Talks to Xen Store to figure out what devices we have.
+/*
+ * Private include for xenbus communications.
  *
  * Copyright (C) 2005 Rusty Russell, IBM Corporation
  * Copyright (C) 2005 XenSource Ltd.
@@ -31,8 +29,8 @@
  * IN THE SOFTWARE.
  */
 
-#ifndef _XENBUS_PROBE_H
-#define _XENBUS_PROBE_H
+#ifndef _XENBUS_XENBUS_H
+#define _XENBUS_XENBUS_H
 
 #define XEN_BUS_ID_SIZE			20
 
@@ -54,35 +52,46 @@ enum xenstore_init {
 	XS_LOCAL,
 };
 
+extern enum xenstore_init xen_store_domain_type;
 extern const struct attribute_group *xenbus_dev_groups[];
 
-extern int xenbus_match(struct device *_dev, struct device_driver *_drv);
-extern int xenbus_dev_probe(struct device *_dev);
-extern int xenbus_dev_remove(struct device *_dev);
-extern int xenbus_register_driver_common(struct xenbus_driver *drv,
-					 struct xen_bus_type *bus,
-					 struct module *owner,
-					 const char *mod_name);
-extern int xenbus_probe_node(struct xen_bus_type *bus,
-			     const char *type,
-			     const char *nodename);
-extern int xenbus_probe_devices(struct xen_bus_type *bus);
+int xs_init(void);
+int xb_init_comms(void);
+void xb_deinit_comms(void);
+int xb_write(const void *data, unsigned int len);
+int xb_read(void *data, unsigned int len);
+int xb_data_to_read(void);
+int xb_wait_for_data_to_read(void);
 
-extern void xenbus_dev_changed(const char *node, struct xen_bus_type *bus);
+int xenbus_match(struct device *_dev, struct device_driver *_drv);
+int xenbus_dev_probe(struct device *_dev);
+int xenbus_dev_remove(struct device *_dev);
+int xenbus_register_driver_common(struct xenbus_driver *drv,
+				  struct xen_bus_type *bus,
+				  struct module *owner,
+				  const char *mod_name);
+int xenbus_probe_node(struct xen_bus_type *bus,
+		      const char *type,
+		      const char *nodename);
+int xenbus_probe_devices(struct xen_bus_type *bus);
 
-extern void xenbus_dev_shutdown(struct device *_dev);
+void xenbus_dev_changed(const char *node, struct xen_bus_type *bus);
 
-extern int xenbus_dev_suspend(struct device *dev);
-extern int xenbus_dev_resume(struct device *dev);
-extern int xenbus_dev_cancel(struct device *dev);
+void xenbus_dev_shutdown(struct device *_dev);
 
-extern void xenbus_otherend_changed(struct xenbus_watch *watch,
-				    const char **vec, unsigned int len,
-				    int ignore_on_shutdown);
+int xenbus_dev_suspend(struct device *dev);
+int xenbus_dev_resume(struct device *dev);
+int xenbus_dev_cancel(struct device *dev);
 
-extern int xenbus_read_otherend_details(struct xenbus_device *xendev,
-					char *id_node, char *path_node);
+void xenbus_otherend_changed(struct xenbus_watch *watch,
+			     const char **vec, unsigned int len,
+			     int ignore_on_shutdown);
+
+int xenbus_read_otherend_details(struct xenbus_device *xendev,
+				 char *id_node, char *path_node);
 
 void xenbus_ring_ops_init(void);
 
+void *xenbus_dev_request_and_reply(struct xsd_sockmsg *msg);
+
 #endif
diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
index 056da6e..23edf53 100644
--- a/drivers/xen/xenbus/xenbus_client.c
+++ b/drivers/xen/xenbus/xenbus_client.c
@@ -47,7 +47,7 @@
 #include <xen/xen.h>
 #include <xen/features.h>
 
-#include "xenbus_probe.h"
+#include "xenbus.h"
 
 #define XENBUS_PAGES(_grants)	(DIV_ROUND_UP(_grants, XEN_PFN_PER_PAGE))
 
diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index ecdecce..c21ec02 100644
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -40,7 +40,7 @@
 #include <asm/xen/hypervisor.h>
 #include <xen/events.h>
 #include <xen/page.h>
-#include "xenbus_comms.h"
+#include "xenbus.h"
 
 static int xenbus_irq;
 
diff --git a/drivers/xen/xenbus/xenbus_comms.h b/drivers/xen/xenbus/xenbus_comms.h
deleted file mode 100644
index 867a2e4..0000000
--- a/drivers/xen/xenbus/xenbus_comms.h
+++ /dev/null
@@ -1,51 +0,0 @@
-/*
- * Private include for xenbus communications.
- *
- * Copyright (C) 2005 Rusty Russell, IBM Corporation
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License version 2
- * as published by the Free Software Foundation; or, when distributed
- * separately from the Linux kernel or incorporated into other
- * software packages, subject to the following license:
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this source file (the "Software"), to deal in the Software without
- * restriction, including without limitation the rights to use, copy, modify,
- * merge, publish, distribute, sublicense, and/or sell copies of the Software,
- * and to permit persons to whom the Software is furnished to do so, subject to
- * the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in
- * all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
- * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
- * IN THE SOFTWARE.
- */
-
-#ifndef _XENBUS_COMMS_H
-#define _XENBUS_COMMS_H
-
-#include <linux/fs.h>
-
-int xs_init(void);
-int xb_init_comms(void);
-void xb_deinit_comms(void);
-
-/* Low level routines. */
-int xb_write(const void *data, unsigned len);
-int xb_read(void *data, unsigned len);
-int xb_data_to_read(void);
-int xb_wait_for_data_to_read(void);
-extern struct xenstore_domain_interface *xen_store_interface;
-extern int xen_store_evtchn;
-extern enum xenstore_init xen_store_domain_type;
-
-extern const struct file_operations xen_xenbus_fops;
-
-#endif /* _XENBUS_COMMS_H */
diff --git a/drivers/xen/xenbus/xenbus_dev_backend.c b/drivers/xen/xenbus/xenbus_dev_backend.c
index 4a41ac9..1126701 100644
--- a/drivers/xen/xenbus/xenbus_dev_backend.c
+++ b/drivers/xen/xenbus/xenbus_dev_backend.c
@@ -16,7 +16,7 @@
 #include <xen/events.h>
 #include <asm/xen/hypervisor.h>
 
-#include "xenbus_comms.h"
+#include "xenbus.h"
 
 static int xenbus_backend_open(struct inode *inode, struct file *filp)
 {
diff --git a/drivers/xen/xenbus/xenbus_dev_frontend.c b/drivers/xen/xenbus/xenbus_dev_frontend.c
index 79130b3..e2bc9b3 100644
--- a/drivers/xen/xenbus/xenbus_dev_frontend.c
+++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
@@ -57,12 +57,12 @@
 #include <linux/miscdevice.h>
 #include <linux/init.h>
 
-#include "xenbus_comms.h"
-
 #include <xen/xenbus.h>
 #include <xen/xen.h>
 #include <asm/xen/hypervisor.h>
 
+#include "xenbus.h"
+
 /*
  * An element of a list of outstanding transactions, for which we're
  * still waiting a reply.
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 4bdf654..6baffbb 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -62,8 +62,7 @@
 
 #include <xen/hvm.h>
 
-#include "xenbus_comms.h"
-#include "xenbus_probe.h"
+#include "xenbus.h"
 
 
 int xen_store_evtchn;
diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
index 37929df..f46b4dc 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -53,8 +53,7 @@
 #include <xen/xenbus.h>
 #include <xen/features.h>
 
-#include "xenbus_comms.h"
-#include "xenbus_probe.h"
+#include "xenbus.h"
 
 /* backend/<type>/<fe-uuid>/<id> => <type>-<fe-domid>-<id> */
 static int backend_bus_id(char bus_id[XEN_BUS_ID_SIZE], const char *nodename)
diff --git a/drivers/xen/xenbus/xenbus_probe_frontend.c b/drivers/xen/xenbus/xenbus_probe_frontend.c
index 6d40a97..d7b77a6 100644
--- a/drivers/xen/xenbus/xenbus_probe_frontend.c
+++ b/drivers/xen/xenbus/xenbus_probe_frontend.c
@@ -27,8 +27,7 @@
 
 #include <xen/platform_pci.h>
 
-#include "xenbus_comms.h"
-#include "xenbus_probe.h"
+#include "xenbus.h"
 
 
 
diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index 6afb993..4c49d87 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -48,8 +48,7 @@
 #include <asm/xen/hypervisor.h>
 #include <xen/xenbus.h>
 #include <xen/xen.h>
-#include "xenbus_comms.h"
-#include "xenbus_probe.h"
+#include "xenbus.h"
 
 struct xs_stored_msg {
 	struct list_head list;
diff --git a/drivers/xen/xenfs/super.c b/drivers/xen/xenfs/super.c
index 8559a71..328c398 100644
--- a/drivers/xen/xenfs/super.c
+++ b/drivers/xen/xenfs/super.c
@@ -16,10 +16,10 @@
 #include <linux/magic.h>
 
 #include <xen/xen.h>
+#include <xen/xenbus.h>
 
 #include "xenfs.h"
 #include "../privcmd.h"
-#include "../xenbus/xenbus_comms.h"
 
 #include <asm/xen/hypervisor.h>
 
diff --git a/drivers/xen/xenfs/xenstored.c b/drivers/xen/xenfs/xenstored.c
index fef20db..82fd2a3 100644
--- a/drivers/xen/xenfs/xenstored.c
+++ b/drivers/xen/xenfs/xenstored.c
@@ -4,9 +4,9 @@
 #include <linux/fs.h>
 
 #include <xen/page.h>
+#include <xen/xenbus.h>
 
 #include "xenfs.h"
-#include "../xenbus/xenbus_comms.h"
 
 static ssize_t xsd_read(struct file *file, char __user *buf,
 			    size_t size, loff_t *off)
diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
index 271ba62..98f73a2 100644
--- a/include/xen/xenbus.h
+++ b/include/xen/xenbus.h
@@ -38,6 +38,7 @@
 #include <linux/notifier.h>
 #include <linux/mutex.h>
 #include <linux/export.h>
+#include <linux/fs.h>
 #include <linux/completion.h>
 #include <linux/init.h>
 #include <linux/slab.h>
@@ -175,16 +176,9 @@ void xs_suspend(void);
 void xs_resume(void);
 void xs_suspend_cancel(void);
 
-/* Used by xenbus_dev to borrow kernel's store connection. */
-void *xenbus_dev_request_and_reply(struct xsd_sockmsg *msg);
-
 struct work_struct;
 
-/* Prepare for domain suspend: then resume or cancel the suspend. */
-void xenbus_suspend(void);
-void xenbus_resume(void);
 void xenbus_probe(struct work_struct *);
-void xenbus_suspend_cancel(void);
 
 #define XENBUS_IS_ERR_READ(str) ({			\
 	if (!IS_ERR(str) && strlen(str) == 0) {		\
@@ -235,4 +229,8 @@ const char *xenbus_strstate(enum xenbus_state state);
 int xenbus_dev_is_online(struct xenbus_device *dev);
 int xenbus_frontend_closed(struct xenbus_device *dev);
 
+extern const struct file_operations xen_xenbus_fops;
+extern struct xenstore_domain_interface *xen_store_interface;
+extern int xen_store_evtchn;
+
 #endif /* _XEN_XENBUS_H */
-- 
2.10.2

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#1565246 — Re: [PATCH v3 3/3] xen: optimize xenbus driver for multiple concurrent xenstore accesses

On 01/23/2017 05:09 AM, Juergen Gross wrote:
> Handling of multiple concurrent Xenstore accesses through xenbus driver
> either from the kernel or user land is rather lame today: xenbus is
> capable to have one access active only at one point of time.
>
> Rewrite xenbus to handle multiple requests concurrently by making use
> of the request id of the Xenstore protocol. This requires to:
>
> - Instead of blocking inside xb_read() when trying to read data from
>   the xenstore ring buffer do so only in the main loop of
>   xenbus_thread().
>
> - Instead of doing writes to the xenstore ring buffer in the context of
>   the caller just queue the request and do the write in the dedicated
>   xenbus thread.
>
> - Instead of just forwarding the request id specified by the caller of
>   xenbus to xenstore use a xenbus internal unique request id. This will
>   allow multiple outstanding requests.
>
> - Modify the locking scheme in order to allow multiple requests being
>   active in parallel.
>
> - Instead of waiting for the reply of a user's xenstore request after
>   writing the request to the xenstore ring buffer return directly to
>   the caller and do the waiting in the read path.
>
> Additionally signal handling was optimized by avoiding waking up the
> xenbus thread or sending an event to Xenstore in case the addressed
> entity is known to be running already.
>
> As a result communication with Xenstore is sped up by a factor of up
> to 5: depending on the request type (read or write) and the amount of
> data transferred the gain was at least 20% (small reads) and went up to
> a factor of 5 for large writes.
>
> In the end some more rough edges of xenbus have been smoothed:
>
> - Handling of memory shortage when reading from xenstore ring buffer in
>   the xenbus driver was not optimal: it was busy looping and issuing a
>   warning in each loop.
>
> - In case of xenstore not running in dom0 but in a stubdom we end up
>   with two xenbus threads running as the initialization of xenbus in
>   dom0 expecting a local xenstored will be redone later when connecting
>   to the xenstore domain. Up to now this was no problem as locking
>   would prevent the two xenbus threads interfering with each other, but
>   this was just a waste of kernel resources.
>
> - An out of memory situation while writing to or reading from the
>   xenstore ring buffer no longer will lead to a possible loss of
>   synchronization with xenstore.
>
> - The user read and write part are now interruptible by signals.
>
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

[toc] | [prev] | [next] | [standalone]

#1565862 — Re: [PATCH v3 3/3] xen: optimize xenbus driver for multiple concurrent xenstore accesses

On 01/23/2017 01:59 PM, Boris Ostrovsky wrote:
> On 01/23/2017 05:09 AM, Juergen Gross wrote:
>> Handling of multiple concurrent Xenstore accesses through xenbus driver
>> either from the kernel or user land is rather lame today: xenbus is
>> capable to have one access active only at one point of time.
>>
>>


This patch appears to break save/restore:

[   39.979281] Freezing user space processes ... (elapsed 0.000 seconds)
done.
[   39.981347] Freezing remaining freezable tasks ... (elapsed 0.000
seconds) done.
[   39.983853] PM: freeze of devices complete after 0.537 msecs
[   39.984955] suspending xenstore...
[  246.751144] INFO: task xenwatch:35 blocked for more than 120 seconds.
[  246.752286]       Not tainted 4.10.0-rc5upstream-00311-g3eda026 #2
[  246.753378] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
disables this message.
[  246.754489] xenwatch        D12056    35      2 0x00000000
[  246.755624] Call Trace:
[  246.756732]  __schedule+0x225/0x6f0
[  246.757834]  schedule+0x3c/0xb0
[  246.758918]  xs_suspend+0x84/0xc0
[  246.759983]  ? woken_wake_function+0x10/0x10
[  246.761039]  do_suspend+0x52/0x190
[  246.762079]  ? xenbus_transaction_end+0x2f/0x40
[  246.763097]  shutdown_handler+0xfc/0x130
[  246.764086]  xenwatch_thread+0xaa/0x150
[  246.765076]  ? woken_wake_function+0x10/0x10
[  246.766042]  ? schedule+0x3c/0xb0
[  246.766951]  ? _raw_spin_unlock_irqrestore+0x15/0x20
[  246.767869]  ? xenbus_printf+0xa0/0xa0
[  246.768603]  kthread+0x109/0x140
[  246.769057]  ? __kthread_init_worker+0x30/0x30
[  246.769514]  ret_from_fork+0x2c/0x40
[  246.769963] NMI backtrace for cpu 1
[  246.770422] CPU: 1 PID: 322 Comm: khungtaskd Not tainted
4.10.0-rc5upstream-00311-g3eda026 #2
[  246.770898] Call Trace:
[  246.771366]  dump_stack+0x67/0x98
[  246.771413]  ? x86_vector_alloc_irqs+0x111/0x1a0
[  246.771413]  nmi_cpu_backtrace+0xae/0xb0
[  246.771413]  ? hw_nmi_get_sample_period+0x20/0x20
[  246.771413]  nmi_trigger_cpumask_backtrace+0x126/0x160
[  246.771413]  arch_trigger_cpumask_backtrace+0x14/0x20
[  246.771413]  watchdog+0x3bf/0x470
[  246.771413]  ? reset_hung_task_detector+0x20/0x20
[  246.771413]  ? schedule+0x3c/0xb0
[  246.771413]  ? _raw_spin_unlock_irqrestore+0x15/0x20
[  246.771413]  ? reset_hung_task_detector+0x20/0x20
[  246.771413]  kthread+0x109/0x140
[  246.771413]  ? proc_cap_handler+0x1a0/0x1a0
[  246.771413]  ? __kthread_init_worker+0x30/0x30
[  246.771413]  ? proc_cap_handler+0x1a0/0x1a0
[  246.771413]  ? proc_cap_handler+0x1a0/0x1a0
[  246.771413]  ret_from_fork+0x2c/0x40
[  246.778690] Sending NMI from CPU 1 to CPUs 0:
[  246.779265] NMI backtrace for cpu 0
[  246.779609] CPU: 0 PID: 0 Comm: swapper/0 Not tainted
4.10.0-rc5upstream-00311-g3eda026 #2
[  246.779961] task: ffffffff81e11500 task.stack: ffffffff81e00000
[  246.780257] RIP: e030:xen_hypercall_sched_op+0xa/0x20
[  246.780257] RSP: e02b:ffffffff81e03dd0 EFLAGS: 00000246
[  246.780257] RAX: 0000000000000000 RBX: ffffffff81e11500 RCX:
ffffffff810013aa
[  246.780257] RDX: 0000000000000001 RSI: deadbeefdeadf00d RDI:
deadbeefdeadf00d
[  246.780257] RBP: ffffffff81e03de8 R08: 0100000000000000 R09:
ffff88003f212940
[  246.780257] R10: 0000000000000000 R11: 0000000000000246 R12:
0000000000000000
[  246.780257] R13: 0000000000000000 R14: ffffffff81e11502 R15:
ffffffff81e11500
[  246.780257] FS:  00007f53626e9700(0000) GS:ffff88003f200000(0000)
knlGS:0000000000000000
[  246.780257] CS:  e033 DS: 0000 ES: 0000 CR0: 0000000080050033
[  246.780257] CR2: ffffffffff600400 CR3: 0000000007616000 CR4:
0000000000042660
[  246.780257] Call Trace:
[  246.780257]  ? xen_safe_halt+0x10/0x20
[  246.780257]  default_idle+0x1d/0x100
[  246.780257]  arch_cpu_idle+0xa/0x10
[  246.780257]  default_idle_call+0x1e/0x30
[  246.780257]  do_idle+0x17c/0x250
[  246.780257]  cpu_startup_entry+0x1d/0x20
[  246.780257]  rest_init+0x80/0x90
[  246.780257]  start_kernel+0x483/0x490
[  246.780257]  ? set_init_arg+0x5e/0x5e
[  246.780257]  x86_64_start_reservations+0x2a/0x2c
[  246.780257]  xen_start_kernel+0x51b/0x51d
[  246.780257] Code: cc 51 41 53 b8 1c 00 00 00 0f 05 41 5b 59 c3 cc cc
cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 51 41 53 b8 1d 00 00 00
0f 05 <41> 5b 59 c3 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc
[  246.952336] Kernel panic - not syncing: hung_task: blocked tasks
[  246.952818] CPU: 1 PID: 322 Comm: khungtaskd Not tainted
4.10.0-rc5upstream-00311-g3eda026 #2
[  246.953318] Call Trace:
[  246.953318]  dump_stack+0x67/0x98
[  246.953318]  panic+0xcd/0x22c
[  246.953318]  ? find_next_bit+0xb/0x10
[  246.953318]  watchdog+0x3cd/0x470
[  246.953318]  ? reset_hung_task_detector+0x20/0x20
[  246.953318]  ? schedule+0x3c/0xb0
[  246.953318]  ? _raw_spin_unlock_irqrestore+0x15/0x20
[  246.953318]  ? reset_hung_task_detector+0x20/0x20
[  246.953318]  kthread+0x109/0x140
[  246.953318]  ? proc_cap_handler+0x1a0/0x1a0
[  246.953318]  ? __kthread_init_worker+0x30/0x30
[  246.953318]  ? proc_cap_handler+0x1a0/0x1a0
[  246.953318]  ? proc_cap_handler+0x1a0/0x1a0
[  246.953318]  ret_from_fork+0x2c/0x40
[  246.953318] Kernel Offset: disabled
-bash-4.1# xl destroy bootstrap-x86_64




-boris

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#1565977 — Re: [PATCH v3 3/3] xen: optimize xenbus driver for multiple concurrent xenstore accesses

On 24/01/17 14:47, Boris Ostrovsky wrote:
> On 01/23/2017 01:59 PM, Boris Ostrovsky wrote:
>> On 01/23/2017 05:09 AM, Juergen Gross wrote:
>>> Handling of multiple concurrent Xenstore accesses through xenbus driver
>>> either from the kernel or user land is rather lame today: xenbus is
>>> capable to have one access active only at one point of time.
>>>
>>>
> 
> 
> This patch appears to break save/restore:

Hmm, tried multiple times, but I can't reproduce this issue.

Anything special in the setup? I tried a 64 bit pv guest and did
"xl save".

Do I have to run some load in parallel?


Juergen

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