[PATCH for-4.22 v2 3/4] xen/irq: handle IRQ being disabled while executing its handler

[Roger Pau Monne <roger.pau@citrix.com>]

It's possible for IRQ_DISABLED to be set while running the handler
execution loop in do_IRQ().  Such disabling can be done by the handler
itself, or from a remote CPU.

Check for IRQ_DISABLED not being set in the loop condition, as to not
execute the handler if the IRQ has been disabled.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
I wanted to add a fixes tag, but this has been broken since forever, and
hence I should add:

Fixes: 4676bbf96dc8 ("bitkeeper revision 1.2 (3ddb79c9KusG02eh7i-uXkgY0IksKA)")

Which is pointless IMO.
---
 xen/arch/x86/irq.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index 739fc04bd16a..2082ad489d74 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -2088,7 +2088,9 @@ void do_IRQ(struct cpu_user_regs *regs)
     desc->status |= IRQ_INPROGRESS;
 
     action = desc->action;
-    while ( desc->status & IRQ_PENDING )
+
+    /* Deal with IRQ_DISABLED being set while inside the loop body. */
+    while ( (desc->status & (IRQ_PENDING | IRQ_DISABLED)) == IRQ_PENDING )
     {
         desc->status &= ~IRQ_PENDING;
         spin_unlock_irq(&desc->lock);
-- 
2.53.0