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From: Jan Beulich <jbeulich@suse.com>
To: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Ian Jackson <iwj@xenproject.org>, Julien Grall <julien@xen.org>,
	Wei Liu <wl@xen.org>, Stefano Stabellini <sstabellini@kernel.org>
Subject: [PATCH v5 3/6] evtchn: slightly defer lock acquire where possible
Date: Wed, 27 Jan 2021 09:16:36 +0100	[thread overview]
Message-ID: <d005ccb8-e4d3-7cc5-3734-c8afeb7b3bb0@suse.com> (raw)
In-Reply-To: <306e62e8-9070-2db9-c959-858465c50c1d@suse.com>

port_is_valid() and evtchn_from_port() are fine to use without holding
any locks. Accordingly acquire the per-domain lock slightly later in
evtchn_close() and evtchn_bind_vcpu().

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
v4: New.

--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -610,17 +610,14 @@ int evtchn_close(struct domain *d1, int
     int            port2;
     long           rc = 0;
 
- again:
-    write_lock(&d1->event_lock);
-
     if ( !port_is_valid(d1, port1) )
-    {
-        rc = -EINVAL;
-        goto out;
-    }
+        return -EINVAL;
 
     chn1 = evtchn_from_port(d1, port1);
 
+ again:
+    write_lock(&d1->event_lock);
+
     /* Guest cannot close a Xen-attached event channel. */
     if ( unlikely(consumer_is_xen(chn1)) && guest )
     {
@@ -1044,16 +1041,13 @@ long evtchn_bind_vcpu(unsigned int port,
     if ( (v = domain_vcpu(d, vcpu_id)) == NULL )
         return -ENOENT;
 
-    write_lock(&d->event_lock);
-
     if ( !port_is_valid(d, port) )
-    {
-        rc = -EINVAL;
-        goto out;
-    }
+        return -EINVAL;
 
     chn = evtchn_from_port(d, port);
 
+    write_lock(&d->event_lock);
+
     /* Guest cannot re-bind a Xen-attached event channel. */
     if ( unlikely(consumer_is_xen(chn)) )
     {



  parent reply	other threads:[~2021-01-27  8:16 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-27  8:13 [PATCH v5 0/6] evtchn: (not so) recent XSAs follow-on Jan Beulich
2021-01-27  8:15 ` [PATCH v5 1/6] evtchn: use per-channel lock where possible Jan Beulich
2021-01-27  8:16 ` [PATCH v5 2/6] evtchn: convert domain event lock to an r/w one Jan Beulich
2021-05-27 11:01   ` Roger Pau Monné
2021-05-27 11:16     ` Jan Beulich
2022-07-07 18:00   ` Julien Grall
2021-01-27  8:16 ` Jan Beulich [this message]
2021-01-27  8:16 ` [PATCH v5 4/6] evtchn: add helper for port_is_valid() + evtchn_from_port() Jan Beulich
2021-01-27  8:17 ` [PATCH v5 5/6] evtchn: type adjustments Jan Beulich
2021-01-27  8:17 ` [PATCH v5 6/6] evtchn: drop acquiring of per-channel lock from send_guest_{global,vcpu}_virq() Jan Beulich
2021-04-21 15:23 ` Ping: [PATCH v5 0/6] evtchn: (not so) recent XSAs follow-on Jan Beulich
2021-04-21 15:56   ` Julien Grall
2021-04-22  8:53     ` Jan Beulich
2021-05-14 15:29       ` Roger Pau Monné
2021-05-17  7:15         ` Jan Beulich

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