[uml-devel] Re: 2.4.27 + 2.4.26-3um - Kernel panic: handle_trap - failed to wait at end of syscall, errno = 4, status = 4479

[uml-devel] Re: 2.4.27 + 2.4.26-3um - Kernel panic: handle_trap - failed to wait at end of syscall, errno = 4, status = 4479

[Christopher S. Aker]

> Filesystem is Slackware 9 (no /lib/tls), will try to test some under gdb...

Forgot to mention, this is 2.4.26-3um with all the incrementals.  Host is 2.6.4, without sysemu.

-Chris


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Re: [uml-devel] Re: 2.4.27 + 2.4.26-3um - Kernel panic: handle_trap - failed to wait at end of syscall, errno = 4, status = 4479

[Christopher S. Aker]

Another tidbit of information...

A user of mind has two UMLs on two different hosts.  Both the UMLs are running Debian unstable.
This kernel on the 2.6.4 host doesn't work, while the other on a 2.6.7+sysemu box does.

-Chris



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RE: [uml-devel] Re: 2.4.27 + 2.4.26-3um - Kernel panic: handle_trap - failed to wait at end of syscall, errno = 4, status = 4479

[Stroesser, Bodo]

[-- Attachment #1: Type: text/plain, Size: 976 bytes --]

Christopher S. Aker said:
>Another tidbit of information...
>
>A user of mind has two UMLs on two different hosts.  Both the UMLs are
running Debian unstable.
>This kernel on the 2.6.4 host doesn't work, while the other on a
2.6.7+sysemu box does.
>
>-Chris

Yes. That's exactly what happened with my uml 2.6.8.1 with the
sysemu-patch. And I can see the same problem in the 2.4.26 sysemu-patch,
that is used in your UML kernel (As the console prinout tells).
If sysemu isn't used, but the patch is applied, the correct sequence of
first nullifying a systemcall on the host and than calling
handle_syscall() in handle_trap() is inverted, what causes the problem.
In 2.6.9 sysemu is implemented correctly.
The attached patch (sorry, can't inline it, due to my silly mailer ...)
will correct the sequence and should let your kernel work with or
without sysemu support.
Please note, this is a patch against 2.6.8.1, you might need to adapt it
a bit.

Bodo

[-- Attachment #2: patch-sysemu-panic --]
[-- Type: application/octet-stream, Size: 1555 bytes --]

--- uml.orig/arch/um/kernel/skas/process.c	2004-09-17 19:20:15.000000000 +0200
+++ uml/arch/um/kernel/skas/process.c	2004-09-21 14:32:22.129327631 +0200
@@ -68,25 +68,25 @@
 		return;
 	}
 
-	handle_syscall(regs);
-	if(use_sysemu)
-		return;
+	if(!use_sysemu) {
+		err = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET, __NR_getpid);
+		if(err < 0)
+			panic("handle_trap - nullifying syscall failed, errno = %d\n",
+			      errno);
 
-	err = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET, __NR_getpid);
-	if(err < 0)
-		panic("handle_trap - nullifying syscall failed, errno = %d\n",
-		      errno);
+		err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
+		if(err < 0)
+			panic("handle_trap - continuing to end of syscall failed, "
+			      "errno = %d\n", errno);
 
-	err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
-	if(err < 0)
-		panic("handle_trap - continuing to end of syscall failed, "
-		      "errno = %d\n", errno);
-
-	CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED));
-	if((err < 0) || !WIFSTOPPED(status) || 
-	   (WSTOPSIG(status) != SIGTRAP))
-		panic("handle_trap - failed to wait at end of syscall, "
-		      "errno = %d, status = %d\n", errno, status);
+		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED));
+		if((err < 0) || !WIFSTOPPED(status) || 
+		   (WSTOPSIG(status) != SIGTRAP))
+			panic("handle_trap - failed to wait at end of syscall, "
+			      "err = %d, errno = %d, status = %x\n", err, errno, status);
+	}
+
+	handle_syscall(regs);
 }
 
 static int userspace_tramp(void *arg)