[xen staging] evtchn: let evtchn_set_priority() acquire the per-channel lock

[patchbot@xxxxxxx]

commit b76c3a1b878b1897b7166a46a8cb341ef6dfa854
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Oct 23 10:12:31 2020 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Oct 23 10:12:31 2020 +0200

    evtchn: let evtchn_set_priority() acquire the per-channel lock
    
    Some lock wants to be held to make sure the port doesn't change state,
    but there's no point holding the per-domain event lock here. Switch to
    using the finer grained per-channel lock instead (albeit as a downside
    for the time being this requires disabling interrupts for a short
    period of time).
    
    FAOD this doesn't guarantee anything towards in particular
    evtchn_fifo_set_pending(), as for interdomain channels that function
    would be called with the remote side's per-channel lock held.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/common/event_channel.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/xen/common/event_channel.c b/xen/common/event_channel.c
index 37d0b75384..cd4a2c0501 100644
--- a/xen/common/event_channel.c
+++ b/xen/common/event_channel.c
@@ -1154,20 +1154,17 @@ static long evtchn_set_priority(const struct 
evtchn_set_priority *set_priority)
 {
     struct domain *d = current->domain;
     unsigned int port = set_priority->port;
+    struct evtchn *chn;
     long ret;
-
-    spin_lock(&d->event_lock);
+    unsigned long flags;
 
     if ( !port_is_valid(d, port) )
-    {
-        spin_unlock(&d->event_lock);
         return -EINVAL;
-    }
 
-    ret = evtchn_port_set_priority(d, evtchn_from_port(d, port),
-                                   set_priority->priority);
-
-    spin_unlock(&d->event_lock);
+    chn = evtchn_from_port(d, port);
+    spin_lock_irqsave(&chn->lock, flags);
+    ret = evtchn_port_set_priority(d, chn, set_priority->priority);
+    spin_unlock_irqrestore(&chn->lock, flags);
 
     return ret;
 }
--
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