[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Allen Chan]

Attached below are some stack traces for the different "linux" threads 
after the guest kernel hangs.  I tried to follow the instructions and 
examples from the Kernel Debugging section of the User Mode Linux 
HOWTO, but am unsure of how to get the stack trace from the "last 
call to schedule()".

I hope the stack traces I have attached helps.  If not, please point 
me in the right direction to getting the stack trace that you are 
looking for.

Thanks.

> This resembles the GHz bug, except that one is fixed.  If someone
> could get a stack trace from the last call to schedule(), that would
> be a help. 
> There is some sort of a deadlock on a semaphore, and I'd like to
> know which one it is.


---------- start of debug session ------------
(906)% gdb linux
GNU gdb 6.1-debian
Copyright 2004 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and 
you are
welcome to change it and/or distribute copies of it under certain 
conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for 
details.
This GDB was configured as "i386-linux"...Using host libthread_db 
library "/lib/tls/libthread_db.so.1".

(gdb) break schedule
Breakpoint 1 at 0xa0011c43: file sched.c, line 557.
(gdb) handle SIGSEGV pass nostop noprint
Signal        Stop      Print   Pass to program Description
SIGSEGV       No        No      Yes             Segmentation fault
(gdb) handle SIGUSR1 pass nostop noprint
Signal        Stop      Print   Pass to program Description
SIGUSR1       No        No      Yes             User defined signal 1
(gdb) r umid=tinyuml mem=16M ubd0=umlfs eth0=daemon
Starting program: /usr/bin/linux umid=tinyuml mem=16M ubd0=umlfs 
eth0=daemon
Detaching after fork from child process 23295.
Checking for the skas3 patch in the host...found
Checking for /proc/mm...found
Detaching after fork from child process 23296.
Detaching after fork from child process 23297.
Detaching after fork from child process 23298.
Detaching after fork from child process 23299.
Checking for /dev/anon on the host...Not available (open failed with 
errno 2)
Linux version 2.4.26-2um (root@swale) (gcc version 3.3.4 (Debian 
1:3.3.4-4)) #2 Tue Jul 27 13:34:29 EDT 2004
On node 0 totalpages: 4096
zone(0): 4096 pages.
zone(1): 0 pages.
zone(2): 0 pages.
Kernel command line: mem=16M ubd0=umlfs eth0=daemon root=/dev/ubd0
Calibrating delay loop... 1648.23 BogoMIPS
Memory: 12112k available
Dentry cache hash table entries: 2048 (order: 2, 16384 bytes)
Inode cache hash table entries: 1024 (order: 1, 8192 bytes)
Mount cache hash table entries: 512 (order: 0, 4096 bytes)
Buffer cache hash table entries: 1024 (order: 0, 4096 bytes)
Page-cache hash table entries: 4096 (order: 2, 16384 bytes)
Checking for host processor cmov support...Yes
Checking for host processor xmm support...No
Checking that ptrace can change system call numbers...Detaching after 
fork from child process 23300.
OK
Checking that host ptys support output SIGIO...Yes
Checking that host ptys support SIGIO on close...No, enabling 
workaround
POSIX conformance testing by UNIFIX
Linux NET4.0 for Linux 2.4
Based upon Swansea University Computer Society NET3.039
Initializing RT netlink socket
Starting kswapd
VFS: Disk quotas vdquot_6.5.1
Journalled Block Device driver loaded
devfs: v1.12c (20020818) Richard Gooch (rgooch@atnf.csiro.au)
devfs: boot_options: 0x0
SGI XFS with ACLs, no debug enabled
SGI XFS Quota Management subsystem
Detaching after fork from child process 23301.
pty: 256 Unix98 ptys configured
RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize
loop: loaded (max 8 devices)
Initializing Cryptographic API
Initializing software serial port version 1
Netdevice 0 : daemon backend (uml_switch version 3) - 
unix:/var/run/uml-utilities/uml_switch.ctl
mconsole (version 2) initialized on /home/alydar/.uml/tinyuml/mconsole
Partition check:
 ubda: unknown partition table
Detaching after fork from child process 23302.
Initializing stdio console driver
Detaching after fork from child process 23303.
                            NET4: Linux TCP/IP 1.0 for NET4.0

Program received signal SIGINT, Interrupt.
0xa02177da in nanosleep () at proc_fs.h:155
155                     res->data=data;
(gdb) bt
#0  0xa02177da in nanosleep () at proc_fs.h:155
#1  0xa0153354 in idle_sleep (secs=-516) at time.c:132
#2  0xa014f091 in cpu_idle () at process_kern.c:212
#3  0xa000f635 in rest_init () at init/main.c:364
#4  0xa00025e6 in start_kernel () at init/main.c:458
#5  0xa015b617 in start_kernel_proc (unused=0x0) at process_kern.c:156
#6  0xa014ead9 in run_kernel_thread (fn=0xa015b5f0 
<start_kernel_proc>, arg=0x0, jmp_ptr=0xfffffdfc) at process.c:227
#7  0xa015b360 in new_thread_handler (sig=10) at process_kern.c:70
#8  <signal handler called>
#9  0xa0219c9d in syscall () at proc_fs.h:155
#10 0xbffff4c8 in ?? ()
#11 0xa020128c in siglongjmp () at proc_fs.h:155
#12 0xa015ae39 in start_idle_thread (stack=0xa02a2000, 
switch_buf_ptr=0xa02a057c, fork_buf_ptr=0x0) at process.c:303
#13 0xa015b678 in start_uml_skas () at process_kern.c:170
#14 0xa0154a3d in linux_main (argc=-1610612736, argv=0xbffff924) at 
um_arch.c:397
#15 0xa000f3ee in main (argc=6, argv=0xbffff924, envp=0xbffff940) at 
arch/um/main.c:148
(gdb) det
Detaching from program: /usr/bin/linux, process 23291
(gdb) att 23296
Attaching to program: /usr/bin/linux, process 23296
ptrace: Operation not permitted.
(gdb) att 23301
Attaching to program: /usr/bin/linux, process 23301
0xa0219c9d in syscall () at proc_fs.h:155
155                     res->data=data;
(gdb) bt
#0  0xa0219c9d in syscall () at proc_fs.h:155
#1  0xa015e945 in io_getevents (ctx_id=4294967292, min_nr=-4, nr=-4, 
events=0xfffffffc, timeout=0xfffffffc) at aio.c:58
#2  0xa015eb09 in aio_thread (arg=0x0) at aio.c:128
#3  0xa0219dda in clone () at proc_fs.h:155
(gdb) det
Detaching from program: /usr/bin/linux, process 23301
(gdb) att 23302
Attaching to program: /usr/bin/linux, process 23302
0xa0218aad in read () at proc_fs.h:155
155                     res->data=data;
(gdb) bt
#0  0xa0218aad in read () at proc_fs.h:155
#1  0xa08d8f84 in ?? ()
#2  0xa015fca4 in file_io (fd=12, buf=0xa08d8f84, len=76, 
io_proc=0xa0218a90 <read>, copy_user_proc=0xa014f440 
<copy_from_user_proc>)
    at file.c:489
#3  0xa015fd41 in os_read_file (fd=-512, buf=0xfffffe00, len=-512) at 
file.c:505
#4  0xa018497a in io_thread (arg=0x0) at ubd_user.c:317
#5  0xa0219dda in clone () at proc_fs.h:155
(gdb) det
Detaching from program: /usr/bin/linux, process 23302
(gdb) att 23303
Attaching to program: /usr/bin/linux, process 23303
0xa0219196 in poll () at proc_fs.h:155
155                     res->data=data;
(gdb) bt
#0  0xa0219196 in poll () at proc_fs.h:155
#1  0xa01500a9 in write_sigio_thread (unused=0x0) at sigio_user.c:190
#2  0xa0219dda in clone () at proc_fs.h:155
(gdb)
---------- end of debug session ------------


---------- ps output for "linux" threads -----------
23290 pts/68   S+     0:01 gdb linux
23291 pts/68   T      0:00 /usr/bin/linux
23296 pts/68   T      0:00 /usr/bin/linux
23301 pts/68   T      0:00 /usr/bin/linux
23302 pts/68   T      0:00 /usr/bin/linux
23303 pts/68   T      0:00 /usr/bin/linux
-------------- end ps output ----------------


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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Jeff Dike]

alydar@users.sourceforge.net said:
> #2  0xa014f091 in cpu_idle () at process_kern.c:212 
> #3  0xa000f635 in rest_init () at init/main.c:364
> #4  0xa00025e6 in start_kernel () at init/main.c:458

This is the problem stack.  One of the init functions is tripping over a
semaphore, and no one has been able to tell me which init function it is
or which semaphore.  Although the down isn't showing in this stack, which is
a bit confusing.

				Jeff



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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Allen Chan]

I had no luck trying to get a better backtrace.  However, since this 
problem only showed up between 2.4.26-1um and 2.4.26-2um, I 
systematically backed out the CVS changes until the problem went 
away.

It turns out that the following changes caused the problem to show up:

arch/um/drivers/chan_kern.c 1.39 Fri 07-16-2004 02:27 PM EDT jdike Exp 
+65 -0
  Moved some non-userspace code from chan_user.c to chan_kern.c.
arch/um/drivers/chan_user.c 1.33 Fri 07-16-2004 02:27 PM EDT jdike Exp 
+0 -64
  Moved some non-userspace code from chan_user.c to chan_kern.c.

I cannot explain why simply moving a few functions from one file to 
another will have any real effect on the resulting kernel, but my 
2.4.26-2um guest kernel is now running fine without these changes.


On Wednesday 28 July 2004 01:22 pm, Jeff Dike wrote:
> alydar@users.sourceforge.net said:
> > #2  0xa014f091 in cpu_idle () at process_kern.c:212
> > #3  0xa000f635 in rest_init () at init/main.c:364
> > #4  0xa00025e6 in start_kernel () at init/main.c:458
>
> This is the problem stack.  One of the init functions is tripping
> over a semaphore, and no one has been able to tell me which init
> function it is or which semaphore.  Although the down isn't showing
> in this stack, which is a bit confusing.
>
> 				Jeff
>


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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Allen Chan]

More details on the problem after some more investigation and 
testing... the specific function that was moved from chan_user.c to 
chan_kern.c that caused the problem is generic_console_write().  
Notice the isatty() calls.  They probably explain the earlier 
observation that piping or redirecting the stdout gets around the 
problem.

int generic_console_write(int fd, const char *buf, int n, void 
*unused)
{
        struct termios save, new;
        int err;

        if(isatty(fd)){
                tcgetattr(fd, &save);
                new = save;
                new.c_oflag |= OPOST;
                tcsetattr(fd, TCSAFLUSH, &new);
        }
        err = generic_write(fd, buf, n, NULL);
        if(isatty(fd)) tcsetattr(fd, TCSAFLUSH, &save);
        return(err);
}

Note also the output for chan_kern.c while the kernel is compiling:

gcc -D__KERNEL__ -I/home/alydar/play/kernel/linux-2.4.26/include -Wall 
-Wstrict-prototypes -Wno-trigraphs -O2 -fno-strict-aliasing 
-fno-common  -U__i386__ -Ui386 -DUM_FASTCALL -g -D__arch_um__ 
-DSUBARCH="i386" -D_LARGEFILE64_SOURCE 
-I/home/alydar/play/kernel/linux-2.4.26/arch/um/include 
-Derrno=kernel_errno 
-I/home/alydar/play/kernel/linux-2.4.26/arch/um/kernel/tt/include 
-I/home/alydar/play/kernel/linux-2.4.26/arch/um/kernel/skas/include    
-nostdinc -iwithprefix include -DKBUILD_BASENAME=chan_kern  -c -o 
chan_kern.o chan_kern.c
chan_kern.c: In function `generic_console_write':
chan_kern.c:121: warning: implicit declaration of function `isatty'
chan_kern.c:122: warning: implicit declaration of function `tcgetattr'
chan_kern.c:125: warning: implicit declaration of function `tcsetattr'


On Thursday 29 July 2004 02:30 pm, Allen Chan wrote:
>
> It turns out that the following changes caused the problem to show
> up:
>
> arch/um/drivers/chan_kern.c 1.39 Fri 07-16-2004 02:27 PM EDT jdike
> Exp +65 -0
>   Moved some non-userspace code from chan_user.c to chan_kern.c.
> arch/um/drivers/chan_user.c 1.33 Fri 07-16-2004 02:27 PM EDT jdike
> Exp +0 -64
>   Moved some non-userspace code from chan_user.c to chan_kern.c.
>


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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Matt Clay]

Jeff Dike wrote:
> 
> The move_console_write patch at http://user-mode-linux.sourceforge.net/patches.html
> backs out this part of that change.
> 
> Can anyone who's seeing this check that it fixes the hang?

Works for me.  What still bothers me is that turning on debugging 
symbols was "fixing" it for me as well.

  - Matt


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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Jeff Dike]

alydar@users.sourceforge.net said:
> More details on the problem after some more investigation and
> testing... the specific function that was moved from chan_user.c to
> chan_kern.c that caused the problem is generic_console_write().
> Notice the isatty() calls.  They probably explain the earlier
> observation that piping or redirecting the stdout gets around the
> problem. 

The move_console_write patch at http://user-mode-linux.sourceforge.net/patches.html
backs out this part of that change.

Can anyone who's seeing this check that it fixes the hang?

				Jeff



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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Allen Chan]

Works for me.  Thanks.

On Friday 30 July 2004 01:19 pm, Matt Clay wrote:
> Jeff Dike wrote:
> > The move_console_write patch at
> > http://user-mode-linux.sourceforge.net/patches.html backs out
> > this part of that change.
> >
> > Can anyone who's seeing this check that it fixes the hang?
>
> Works for me.  What still bothers me is that turning on debugging
> symbols was "fixing" it for me as well.
>
>   - Matt


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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Jeff Dike]

mattclay@hevanet.com said:
> Works for me.  What still bothers me is that turning on debugging
> symbols was "fixing" it for me as well.

Yeah, this definitely needs more investigation.

				Jeff



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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Allen Chan]

FYI... The same problem occurs in the 2.6.7-1um kernel after applying 
the remove-user-code patch from the "Current patches" site.  Except 
this time, instead of hanging, the guest kernel simply exits without 
warning.  The last output lines before exiting were:

...... [snipped] ......
Initializing stdio console driver
kjournald starting.  Commit interval 5 seconds

While compiling chan_kern.c, the following warnings were issued:

  CC      arch/um/drivers/chan_kern.o
arch/um/drivers/chan_kern.c: In function `generic_console_write':
arch/um/drivers/chan_kern.c:121: warning: implicit declaration of 
function `isatty'
arch/um/drivers/chan_kern.c:122: warning: implicit declaration of 
function `tcgetattr'
arch/um/drivers/chan_kern.c:125: warning: implicit declaration of 
function `tcsetattr'
arch/um/drivers/chan_kern.c: At top level:
arch/um/drivers/chan_kern.c:79: warning: `not_configged_ops' defined 
but not used

While isatty() is in <unistd.h> and tcgetattr() and tcsetattr() are in 
<termios.h> in /usr/include, there does not appear to exist 
equivalent kernel header files that will make those warnings go away 
for chan_kern.c.  Do these functions have to be implemented 
differently if placed at the kernel level?

On Friday 30 July 2004 02:49 pm, Jeff Dike wrote:
> Yeah, this definitely needs more investigation.



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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Daniel Heemann]

On Friday 30 July 2004 19:23, Jeff Dike wrote:
> The move_console_write patch at
> http://user-mode-linux.sourceforge.net/patches.html backs out this part
> of that change.
>
> Can anyone who's seeing this check that it fixes the hang?
>
> 				Jeff

Fixes the hang here, too.

Regards
Daniel

-- 
"Those who would give up essential liberty, to purchase a little temporary 
safety, deserve neither liberty nor safety."  - Benjamin Franklin


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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Nicholas Lee]

On Fri, Jul 30, 2004 at 01:23:40PM -0400, Jeff Dike wrote:
> Can anyone who's seeing this check that it fixes the hang?

Yep.

Nicholas


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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Jeff Dike]

On Fri, Jul 30, 2004 at 05:44:00PM -0400, Allen Chan wrote:
> While isatty() is in <unistd.h> and tcgetattr() and tcsetattr() are in 
> <termios.h> in /usr/include, there does not appear to exist 
> equivalent kernel header files that will make those warnings go away 
> for chan_kern.c.  Do these functions have to be implemented 
> differently if placed at the kernel level?

No, because there really is no difference.  There are "user" files and 
"kernel" files only because user files include libc headers and kernel
files include kernel headers, and you can't mix kernel and libc headers
in the same file.

Possibly, in the libc headers, isatty et al, are macros which expand to
calling something else.  When you use kernel headers without those definitions,
you might get some functions with those names that do the wrong thing somehow.

It would be interesting to see a cpp expansion of that function in both
chan_user.c and chan_kern.c

				Jeff


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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Matt Clay]

Jeff Dike wrote:
> 
>>Works for me.  What still bothers me is that turning on debugging
>>symbols was "fixing" it for me as well.
> 
> Yeah, this definitely needs more investigation.

Looking at the code for generic_console_write I noticed the return codes 
for tcgetattr and tcsetattr are not being checked.  After I added checks 
for the return codes, I found out that both calls to tcsetattr always 
return a non-zero status, which, according to the man pages, indicates a 
failure.  I have no idea if that is important or not.

This happens with or without the patch you supplied.

BTW: I also noticed that commenting out the second call to tcsetattr 
makes the problem go away as well.

  - Matt


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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Matt Clay]

Jeff Dike wrote:
> 
>>Works for me.  What still bothers me is that turning on debugging
>>symbols was "fixing" it for me as well.
> 
> Yeah, this definitely needs more investigation.

This patch seems to fix the problem by adding error handling to
the tcsetattr call in generic_console_write.

  - Matt

--- um.orig/arch/um/drivers/chan_kern.c	2004-07-26 11:43:52.000000000 -0700
+++ um/arch/um/drivers/chan_kern.c	2004-07-31 19:38:51.000000000 -0700
@@ -117,15 +117,15 @@
  {
  	struct termios save, new;
  	int err;
+	int changed = 0;

-	if(isatty(fd)){
-		tcgetattr(fd, &save);
+	if(isatty(fd) && tcgetattr(fd, &save) == 0) {
  		new = save;
  		new.c_oflag |= OPOST;
-		tcsetattr(fd, TCSAFLUSH, &new);
+		if(tcsetattr(fd, TCSAFLUSH, &new) == 0) changed = 1;
  	}
  	err = generic_write(fd, buf, n, NULL);
-	if(isatty(fd)) tcsetattr(fd, TCSAFLUSH, &save);
+	if(changed) tcsetattr(fd, TCSAFLUSH, &save);
  	return(err);
  }



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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Matt Clay]

[-- Attachment #1: Type: text/plain, Size: 237 bytes --]

Matt Clay wrote:
> 
> This patch seems to fix the problem by adding error handling to
> the tcsetattr call in generic_console_write.

Looks like pasting the patch inline wasn't a good idea.  I've attached the 
patch this time.

  - Matt

[-- Attachment #2: tcsetattr_check --]
[-- Type: text/plain, Size: 616 bytes --]

--- um.orig/arch/um/drivers/chan_kern.c	2004-07-26 11:43:52.000000000 -0700
+++ um/arch/um/drivers/chan_kern.c	2004-07-31 19:38:51.000000000 -0700
@@ -117,15 +117,15 @@
 {
 	struct termios save, new;
 	int err;
+	int changed = 0;
 
-	if(isatty(fd)){
-		tcgetattr(fd, &save);
+	if(isatty(fd) && tcgetattr(fd, &save) == 0) {
 		new = save;
 		new.c_oflag |= OPOST;
-		tcsetattr(fd, TCSAFLUSH, &new);
+		if(tcsetattr(fd, TCSAFLUSH, &new) == 0) changed = 1;
 	}
 	err = generic_write(fd, buf, n, NULL);
-	if(isatty(fd)) tcsetattr(fd, TCSAFLUSH, &save);
+	if(changed) tcsetattr(fd, TCSAFLUSH, &save);
 	return(err);
 }
 

Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Jeff Dike]

On Sat, Jul 31, 2004 at 08:28:39PM -0700, Matt Clay wrote:
> This patch seems to fix the problem by adding error handling to
> the tcsetattr call in generic_console_write.

What are the errnos from the failures?

				Jeff


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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Matt Clay]

Jeff Dike wrote:
> 
>>This patch seems to fix the problem by adding error handling to
>>the tcsetattr call in generic_console_write.
> 
> What are the errnos from the failures?

When it does fail (it is not consistent), errno retains whatever value 
it had before tcsetattr was called.  After tcsetattr fails, calling 
tcgetattr shows c_oflag is unchanged.

  - Matt


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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Allen Chan]

After a little poking around, it appears that chan_kern.c and 
chan_user.c have very different interpretations of what struct 
termios should be . On my debian unstable system,

In chan_kern.c:
	sizeof(struct termios) == 36

In chan_user.c:
	sizeof(struct termios) == 60

It appears that the tcgetattr() and tcsetattr() calls are expecting 
pointers to structures of size 60, but are getting pointers to 
structures of size 36 instead when placed inside chan_kern.c.  On a 
tcgetattr() call, the next 24 bytes on the stack after the local 
structure become open game for memory corruption.  On a tcsetattr() 
call, actions may be taken based on 24 bytes worth of data which is 
likely to be garbage.


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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Matt Clay]

Allen Chan wrote:
> After a little poking around, it appears that chan_kern.c and 
> chan_user.c have very different interpretations of what struct 
> termios should be . On my debian unstable system,

Now that you point it out, I see the same thing on my Slackware 10 system.

Here is the definition in my /usr/include/bits/termios.h

typedef unsigned char	cc_t;
typedef unsigned int	speed_t;
typedef unsigned int	tcflag_t;

#define NCCS 32
struct termios
   {
     tcflag_t c_iflag;		/* input mode flags */
     tcflag_t c_oflag;		/* output mode flags */
     tcflag_t c_cflag;		/* control mode flags */
     tcflag_t c_lflag;		/* local mode flags */
     cc_t c_line;			/* line discipline */
     cc_t c_cc[NCCS];		/* control characters */
     speed_t c_ispeed;		/* input speed */
     speed_t c_ospeed;		/* output speed */
   };

And the one from um/include/asm/arch/termbits.h

typedef unsigned char	cc_t;
typedef unsigned int	speed_t;
typedef unsigned int	tcflag_t;

#define NCCS 19
struct termios {
	tcflag_t c_iflag;		/* input mode flags */
	tcflag_t c_oflag;		/* output mode flags */
	tcflag_t c_cflag;		/* control mode flags */
	tcflag_t c_lflag;		/* local mode flags */
	cc_t c_line;			/* line discipline */
	cc_t c_cc[NCCS];		/* control characters */
};

This would certainly explain the random behavior I've been seeing with calls 
to tcsetattr failing sometimes.

  - Matt


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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Matt Clay]

Allen Chan wrote:
> After a little poking around, it appears that chan_kern.c and 
> chan_user.c have very different interpretations of what struct 
> termios should be . On my debian unstable system,

I updated my um/include/asm/arch/termbits.h to match the standard 60 byte 
termios struct, and this fixed the kernel hang during boot.  However, it did 
not make the random failures on calls to tcsetattr go away.

The result is that I sometimes get the following during boot:

<snip>
NET4: Linux TCP/IP 1.0 for NET4.0
                                  IP Protocols: ICMP, UDP, TCP
IP: routing cache hash table of 512 buckets, 4Kbytes
<snip>

Instead of the correct output:

<snip>
NET4: Linux TCP/IP 1.0 for NET4.0
IP Protocols: ICMP, UDP, TCP
IP: routing cache hash table of 512 buckets, 4Kbytes
<snip>

Notice the indented "IP Protocols"?  That's where tcsetattr failed.

  - Matt


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[uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Jeff Dike]

allen@home0.com said:
> It appears that the tcgetattr() and tcsetattr() calls are expecting
> pointers to structures of size 60, but are getting pointers to
> structures of size 36 instead when placed inside chan_kern.c.  On a
> tcgetattr() call, the next 24 bytes on the stack after the local
> structure become open game for memory corruption.  On a tcsetattr()
> call, actions may be taken based on 24 bytes worth of data which is
> likely to be garbage. 

Right, this looks like a real explanation.  Thanks for chasing it down.

				Jeff



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Re: [uml-devel] Re: Bug#260111: user-mode-linux: upgrade hangs at "NET4: Linux TCP/IP 1.0 for NET4.0 "

[Matt Clay]

Jeff Dike wrote:
> 
>>This patch seems to fix the problem by adding error handling to
>>the tcsetattr call in generic_console_write.
> 
> What are the errnos from the failures?

Ignore what I said before about errno not being set, I was wrong.

The answer is that tcsetattr is failing with EINTR rather frequently. 
It never seems to happen when running UML on a real console, but quite 
frequently from inside xterm, konsole or gnome-terminal.

  - Matt


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