kern: awake & dev9p: do not interrupt Tflush to avoid consuming all tags

sys/src/kern/port/awake.c

@@ -239,6 +239,19 @@ awake_fell_asleep(Proc *p)
 	}
 }
 
+Syscalls
+awake_disable(void)
+{
+	Syscalls blockingsc = up->wakeups[up->notified].blockingsc;
+	up->wakeups[up->notified].blockingsc = 0;
+	return blockingsc;
+}
+void
+awake_enable(Syscalls s)
+{
+	up->wakeups[up->notified].blockingsc = s;
+}
+
 int
 awake_should_wake_up(Proc *p)
 {

sys/src/kern/port/dev9p.c

@@ -805,6 +805,7 @@ mountio(Mnt *mnt, Mntrpc *r)
 {
 	Block *b;
 	int n;
+	Syscalls awksysc;
 
 	while(waserror()) {
 		if(mnt->rip == up)
@@ -854,7 +855,28 @@ mountio(Mnt *mnt, Mntrpc *r)
 		if(mnt->rip == nil)
 			break;
 		unlock(&mnt->l);
+		if(r->request.type == Tflush){
+			/* Tflush must not be interrupted by awake
+			 * or we will consume all tags trying: since
+			 * awake cannot know that it's not worth to
+			 * flush an interrupted flush it will interrupt
+			 * them all and each interrupt will cause
+			 * a new flush to be sent.
+			 *
+			 * TODO: verify we do not have to do the same
+			 * with notes
+			 */
+			awksysc = awake_disable();
+			if(waserror()){
+				awake_enable(awksysc);
+				nexterror();
+			}
+		}
 		sleep(r->z, rpcattn, r);
+		if(r->request.type == Tflush){
+			awake_enable(awksysc);
+			poperror();
+		}
 		if(r->done){
 			poperror();
 			mntflushfree(mnt, r);

sys/src/kern/port/portfns.h

@@ -33,6 +33,8 @@ Block*		allocb(int);
 Block*		allocbalign(int, int);
 int		anyhigher(void);
 int		anyready(void);
+Syscalls	awake_disable(void);
+void		awake_enable(Syscalls s);
 void		awake_tick(unsigned long tick);
 void		awake_timer(void*);
 void		awake_ringer(void*);