NetBSD Problem Report #50395

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Message-Id: <20151102160550.08718A6558@mollari.NetBSD.org>
Date: Mon,  2 Nov 2015 16:05:50 +0000 (UTC)
From: vchaves@ymail.com
Reply-To: vchaves@ymail.com
To: gnats-bugs@NetBSD.org
Subject: Loss of characters in serial port communication between gdb and kgdb_stub
X-Send-Pr-Version: www-1.0

>Number:         50395
>Category:       kern
>Synopsis:       Loss of characters in serial port communication between gdb and kgdb_stub
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          closed
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Nov 02 16:10:00 +0000 2015
>Closed-Date:    Sun Nov 08 04:39:51 +0000 2015
>Last-Modified:  Sun Nov 08 04:39:51 +0000 2015
>Originator:     Vicente Chaves
>Release:        Netbsd7-current
>Organization:
>Environment:
NetBSD netbsd7.vbox.lab 7.99.21 NetBSD 7.99.21 (GENERIC) #1: Sat Aug 22 15:46:52 UTC 2015  vchaves@netbsd7.vbox.lab:/home/vchaves/current/amd64/sys/arch/amd64/compile/GENERIC amd64
>Description:
During a kernel debug session using the kgdb we can observe
losses that cause communication problems between the stub and the gdb remote.

This is because despite the com0 be reserved for kgdb, the port continues
generating interrupts when characters available on UART, this makes
the interrupt handler comintr() take the character before the stub.

Analyzing the problem, it seems to me that the function comenabledebugport() at com.c:380,
as suggested by the comment, should use the flag IER_ERLS to call the line break interrupt
instead of the flag IER_ERXRDY, as we can see their definitions in comreg. h

#define IER_ERLS 0x4 Enable line status interrupt
#define IER_ERXRDY 0x1 Enable receiver interrupt

Although it is not related to the above problem, it seems to me that the same mistake seems to occur also in comshutdown() at com.c:815.

After these fixes the stub can communicate seamlessly with the gdb remote.
Best regards
Vicente.
>How-To-Repeat:
Try to debug the kernel using kgdb between two vbox VM.
>Fix:
Index: sys/dev/ic/com.c
===================================================================
RCS file: /cvsroot/src/sys/dev/ic/com.c,v
retrieving revision 1.336
diff -u -r1.336 com.c
--- sys/dev/ic/com.c    4 May 2015 22:59:36 -0000       1.336
+++ sys/dev/ic/com.c    2 Nov 2015 14:45:52 -0000
@@ -377,7 +377,7 @@
 {

        /* Turn on line break interrupt, set carrier. */
-       sc->sc_ier = IER_ERXRDY;
+       sc->sc_ier = IER_ERLS;
        if (sc->sc_type == COM_TYPE_PXA2x0)
                sc->sc_ier |= IER_EUART | IER_ERXTOUT;
        if (sc->sc_type == COM_TYPE_INGENIC ||
@@ -812,7 +812,7 @@

        /* Turn off interrupts. */
        if (ISSET(sc->sc_hwflags, COM_HW_CONSOLE)) {
-               sc->sc_ier = IER_ERXRDY; /* interrupt on break */
+               sc->sc_ier = IER_ERLS; /* interrupt on break */
                if ((sc->sc_type == COM_TYPE_PXA2x0) ||
                    (sc->sc_type == COM_TYPE_INGENIC) ||
                    (sc->sc_type == COM_TYPE_TEGRA))

>Release-Note:

>Audit-Trail:
From: christos@zoulas.com (Christos Zoulas)
To: gnats-bugs@NetBSD.org, kern-bug-people@netbsd.org, 
	gnats-admin@netbsd.org, netbsd-bugs@netbsd.org
Cc: 
Subject: Re: kern/50395: Loss of characters in serial port communication between gdb and kgdb_stub
Date: Mon, 2 Nov 2015 11:24:00 -0500

 On Nov 2,  4:10pm, vchaves@ymail.com (vchaves@ymail.com) wrote:
 -- Subject: kern/50395: Loss of characters in serial port communication betwe

 Perhaps this?

 --- com.c       4 May 2015 22:59:36 -0000       1.336
 +++ com.c       2 Nov 2015 16:23:11 -0000
 @@ -377,7 +377,7 @@
  {

         /* Turn on line break interrupt, set carrier. */
 -       sc->sc_ier = IER_ERXRDY;
 +       sc->sc_ier = IER_ERLS;
         if (sc->sc_type == COM_TYPE_PXA2x0)
                 sc->sc_ier |= IER_EUART | IER_ERXTOUT;
         if (sc->sc_type == COM_TYPE_INGENIC ||
 @@ -812,7 +812,10 @@

         /* Turn off interrupts. */
         if (ISSET(sc->sc_hwflags, COM_HW_CONSOLE)) {
 -               sc->sc_ier = IER_ERXRDY; /* interrupt on break */
 +               if (ISSET(sc->sc_hwflags, COM_HW_KGDB))
 +                       sc->sc_ier = IER_ERLS; /* interrupt on line break */
 +               else
 +                       sc->sc_ier = IER_ERXRDY; /* interrupt on receive */
                 if ((sc->sc_type == COM_TYPE_PXA2x0) ||
                     (sc->sc_type == COM_TYPE_INGENIC) ||
                     (sc->sc_type == COM_TYPE_TEGRA))


 Or do we always want ERLS on shutdown?

 christos

From: Vicente Chaves de Melo <vchaves@ymail.com>
To: gnats-bugs@NetBSD.org
Cc: 
Subject: Re: kern/50395: Loss of characters in serial port communication
 between gdb and kgdb_stub
Date: Mon, 2 Nov 2015 15:29:55 -0200

 Hey Christos,
 about fix in function comshutdown () I stand by my suggestion.

 I believe that changing the flag IER_ERXRDY to IER_ERLS we will obtain 
 the following two benefits

 1) there will be no more interruptions generated for this COM after the 
 shutdown. That would seem to be the intent of this part of the code.

 2) Allow the user to enter the debugger even after the shutdown, sending 
 a BREAK on the serial port.

 I also believe that it wasn't such a wise idea to mix the com_shutdown 
 subject in the same PR problem with kgdb.
 Wouldn't it be better if I open another PR to deal with this matter?

 Best regards
 Vicente.

 On 02/11/2015 14:25, Christos Zoulas wrote:
 > The following reply was made to PR kern/50395; it has been noted by GNATS.
 >
 > From: christos@zoulas.com (Christos Zoulas)
 > To: gnats-bugs@NetBSD.org, kern-bug-people@netbsd.org,
 > 	gnats-admin@netbsd.org, netbsd-bugs@netbsd.org
 > Cc:
 > Subject: Re: kern/50395: Loss of characters in serial port communication between gdb and kgdb_stub
 > Date: Mon, 2 Nov 2015 11:24:00 -0500
 >
 >   On Nov 2,  4:10pm, vchaves@ymail.com (vchaves@ymail.com) wrote:
 >   -- Subject: kern/50395: Loss of characters in serial port communication betwe
 >   
 >   Perhaps this?
 >   
 >   --- com.c       4 May 2015 22:59:36 -0000       1.336
 >   +++ com.c       2 Nov 2015 16:23:11 -0000
 >   @@ -377,7 +377,7 @@
 >    {
 >    
 >           /* Turn on line break interrupt, set carrier. */
 >   -       sc->sc_ier = IER_ERXRDY;
 >   +       sc->sc_ier = IER_ERLS;
 >           if (sc->sc_type == COM_TYPE_PXA2x0)
 >                   sc->sc_ier |= IER_EUART | IER_ERXTOUT;
 >           if (sc->sc_type == COM_TYPE_INGENIC ||
 >   @@ -812,7 +812,10 @@
 >    
 >           /* Turn off interrupts. */
 >           if (ISSET(sc->sc_hwflags, COM_HW_CONSOLE)) {
 >   -               sc->sc_ier = IER_ERXRDY; /* interrupt on break */
 >   +               if (ISSET(sc->sc_hwflags, COM_HW_KGDB))
 >   +                       sc->sc_ier = IER_ERLS; /* interrupt on line break */
 >   +               else
 >   +                       sc->sc_ier = IER_ERXRDY; /* interrupt on receive */
 >                   if ((sc->sc_type == COM_TYPE_PXA2x0) ||
 >                       (sc->sc_type == COM_TYPE_INGENIC) ||
 >                       (sc->sc_type == COM_TYPE_TEGRA))
 >   
 >   
 >   Or do we always want ERLS on shutdown?
 >   
 >   christos
 >   

From: christos@zoulas.com (Christos Zoulas)
To: gnats-bugs@NetBSD.org, kern-bug-people@netbsd.org, 
	gnats-admin@netbsd.org, netbsd-bugs@netbsd.org, vchaves@ymail.com
Cc: 
Subject: Re: kern/50395: Loss of characters in serial port communication between gdb and kgdb_stub
Date: Mon, 2 Nov 2015 12:43:00 -0500

 On Nov 2,  5:35pm, vchaves@ymail.com (Vicente Chaves de Melo) wrote:
 -- Subject: Re: kern/50395: Loss of characters in serial port communication b

 | The following reply was made to PR kern/50395; it has been noted by GNATS.
 | 
 | From: Vicente Chaves de Melo <vchaves@ymail.com>
 | To: gnats-bugs@NetBSD.org
 | Cc: 
 | Subject: Re: kern/50395: Loss of characters in serial port communication
 |  between gdb and kgdb_stub
 | Date: Mon, 2 Nov 2015 15:29:55 -0200
 | 
 |  Hey Christos,
 |  about fix in function comshutdown () I stand by my suggestion.
 |  
 |  I believe that changing the flag IER_ERXRDY to IER_ERLS we will obtain 
 |  the following two benefits
 |  
 |  1) there will be no more interruptions generated for this COM after the 
 |  shutdown. That would seem to be the intent of this part of the code.
 |  
 |  2) Allow the user to enter the debugger even after the shutdown, sending 
 |  a BREAK on the serial port.
 |  
 |  I also believe that it wasn't such a wise idea to mix the com_shutdown 
 |  subject in the same PR problem with kgdb.
 |  Wouldn't it be better if I open another PR to deal with this matter?

 Sure, I agree with the current changes. If you want, please open another
 PR to fix the shutdown issue in a better way. 

 Thanks,

 christos

From: "Christos Zoulas" <christos@netbsd.org>
To: gnats-bugs@gnats.NetBSD.org
Cc: 
Subject: PR/50395 CVS commit: src/sys/dev/ic
Date: Mon, 2 Nov 2015 12:45:13 -0500

 Module Name:	src
 Committed By:	christos
 Date:		Mon Nov  2 17:45:13 UTC 2015

 Modified Files:
 	src/sys/dev/ic: com.c

 Log Message:
 PR/50395: Vicente Chaves de Melo: Loss of characters in serial port
 communication between gdb and kgdb_stub: switch to line break interrupt
 both when entering KGDB and also on shutdown so we can re-enter the debugger
 with BREAK.


 To generate a diff of this commit:
 cvs rdiff -u -r1.336 -r1.337 src/sys/dev/ic/com.c

 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.

From: Vicente Chaves de Melo <vchaves@ymail.com>
To: Christos Zoulas <christos@zoulas.com>, gnats-bugs@NetBSD.org,
 kern-bug-people@netbsd.org, gnats-admin@netbsd.org, netbsd-bugs@netbsd.org
Cc: 
Subject: Re: kern/50395: Loss of characters in serial port communication
 between gdb and kgdb_stub
Date: Sun, 8 Nov 2015 00:20:47 -0200

 On 02/11/2015 15:43, Christos Zoulas wrote:
 > On Nov 2,  5:35pm, vchaves@ymail.com (Vicente Chaves de Melo) wrote:
 > -- Subject: Re: kern/50395: Loss of characters in serial port communication b
 >
 > | The following reply was made to PR kern/50395; it has been noted by GNATS.
 > |
 > | From: Vicente Chaves de Melo <vchaves@ymail.com>
 > | To: gnats-bugs@NetBSD.org
 > | Cc:
 > | Subject: Re: kern/50395: Loss of characters in serial port communication
 > |  between gdb and kgdb_stub
 > | Date: Mon, 2 Nov 2015 15:29:55 -0200
 > |
 > |  Hey Christos,
 > |  about fix in function comshutdown () I stand by my suggestion.
 > |
 > |  I believe that changing the flag IER_ERXRDY to IER_ERLS we will obtain
 > |  the following two benefits
 > |
 > |  1) there will be no more interruptions generated for this COM after the
 > |  shutdown. That would seem to be the intent of this part of the code.
 > |
 > |  2) Allow the user to enter the debugger even after the shutdown, sending
 > |  a BREAK on the serial port.
 > |
 > |  I also believe that it wasn't such a wise idea to mix the com_shutdown
 > |  subject in the same PR problem with kgdb.
 > |  Wouldn't it be better if I open another PR to deal with this matter?
 >
 > Sure, I agree with the current changes. If you want, please open another
 > PR to fix the shutdown issue in a better way.
 >
 > Thanks,
 >
 > christos
 Hey Christos,
 I noticed that you already applied the fixes, so I don't think it's 
 necessary to open a new PR.
 I believe that this PR can be close.
 Thank you very much
 Vicente.

State-Changed-From-To: open->closed
State-Changed-By: christos@NetBSD.org
State-Changed-When: Sat, 07 Nov 2015 23:39:51 -0500
State-Changed-Why:
patch applied to head


>Unformatted:

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