x86/intr: allow mutex recursion in intr_remove_handler

This is needed so interrupt handlers can be removed while the PIC is
resuming, it was previously not possible due to intr_resume holding the
intr_table_lock and intr_remove_handler recursing on it.

Sponsored by:		Citrix Systems R&D
Reviewed by:		kib (previous version)
MFC after:		2 weeks
Differential Revision:	https://reviews.freebsd.org/D4114

1 files changed, 12 insertions, 3 deletions

diff --git a/sys/x86/x86/intr_machdep.c b/sys/x86/x86/intr_machdep.c
index d81c9132dd8c..35ec99253be4 100644
--- a/sys/x86/x86/intr_machdep.c
+++ b/sys/x86/x86/intr_machdep.c
@@ -197,19 +197,28 @@ int
 intr_remove_handler(void *cookie)
 {
 	struct intsrc *isrc;
-	int error;
+	int error, mtx_owned;
 
 	isrc = intr_handler_source(cookie);
 	error = intr_event_remove_handler(cookie);
 	if (error == 0) {
-		mtx_lock(&intr_table_lock);
+		/*
+		 * Recursion is needed here so PICs can remove interrupts
+		 * while resuming. It was previously not possible due to
+		 * intr_resume holding the intr_table_lock and
+		 * intr_remove_handler recursing on it.
+		 */
+		mtx_owned = mtx_owned(&intr_table_lock);
+		if (mtx_owned == 0)
+			mtx_lock(&intr_table_lock);
 		isrc->is_handlers--;
 		if (isrc->is_handlers == 0) {
 			isrc->is_pic->pic_disable_source(isrc, PIC_NO_EOI);
 			isrc->is_pic->pic_disable_intr(isrc);
 		}
 		intrcnt_updatename(isrc);
-		mtx_unlock(&intr_table_lock);
+		if (mtx_owned == 0)
+			mtx_unlock(&intr_table_lock);
 	}
 	return (error);
 }