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kbdfs: send interrupt note in separate proc to prevent potential deadlock

--- a/sys/src/cmd/aux/kbdfs/kbdfs.c

+++ b/sys/src/cmd/aux/kbdfs/kbdfs.c

@@ -113,6 +113,7 @@

 Channel *conschan;	/* chan(char*) */

 Channel *kbdchan;	/* chan(char*) */

+Channel *intchan;	/* chan(int) */

 /*

  * The codes at 0x79 and 0x7b are produced by the PFU Happy Hacking keyboard.

@@ -544,6 +545,21 @@

 }

 /*

+ * Need to do this in a separate proc because if process we're interrupting

+ * is dying and trying to print tombstone, kernel is blocked holding p->debug lock.

+ */

+void

+intrproc(void *)

+{

+	threadsetname("intrproc");

+

+	for(;;){

+		if(recv(intchan, nil) > 0)

+			write(notefd, "interrupt", 9);

+	}

+}

+

+/*

  * Cook lines for cons

  */

 void

@@ -565,9 +581,8 @@

 			recv(cook, &r);

 			switch(r){

 			case Kdel:

-				if(notefd < 0)

+				if(nbsend(intchan, &notefd) <= 0)

 					continue;

-				write(notefd, "interrupt", 9);

 				/* no break */

 			case '\0':	/* flush */

 				nr = 0;

@@ -711,6 +726,8 @@

 		proccreate(scanproc, nil, STACK);	/* scanfd -> keychan */

 	if(consfd >= 0)

 		proccreate(consproc, nil, STACK);	/* consfd -> runechan */

+	if(notefd >= 0)

+		proccreate(intrproc, nil, STACK);	/* intchan -> notefd */

 	threadcreate(keyproc, nil, STACK);		/* keychan -> rawchan, kbdchan */

 	threadcreate(runeproc, nil, STACK);		/* rawchan -> runechan */

@@ -1382,6 +1399,7 @@

 	runechan = chancreate(sizeof(Rune), 32);

 	conschan = chancreate(sizeof(char*), 16);

 	kbdchan = chancreate(sizeof(char*), 16);

+	intchan = chancreate(sizeof(int), 0);

 	elevate();

 	procrfork(ctlproc, nil, STACK, RFNAMEG|RFNOTEG);