[uml-devel] FYI: Re bug report [ 745826 ] run cat /dev/urandom

[uml-devel] FYI: Re bug report [ 745826 ] run cat /dev/urandom

[Struan Bartlett]

Posted to SourceForge:

For the record, this is not entirely fixed. I'm running a Debian host
with 2.4.25 kernel and host-skas3-2.4.25.patch, and a Debian
guest with 2.4.27 kernel and uml-patch-2.4.26-3.

In one xterm I ran "while true; do ls -la /dev/*; done" (see
also bug report 617709). In the other, "cat /dev/urandom".
After 5-10 seconds, the 'linux' host process crashes
completely with:

Scheduling in interrupt
Kernel panic: kernel BUG at sched.c:564!

In interrupt handler - not syncing
 <6>SysRq : Show Regs

EIP: 0023:[<400e4b38>] CPU: 0 Not tainted ESP: 002b:bffffc68
EFLAGS: 00000246
    Not tainted
EAX: ffffffda EBX: 00000001 ECX: 0804cdf0 EDX: 00001000
ESI: 00001000 EDI: 0804cdf0 EBP: bffffc88 DS: 002b ES: 002b
Call Trace: [<a0010e5f>] [<a00cae60>] [<a018db51>]
[<a018dade>] [<a000dc93>] 
   [<a00cade9>] [<a00b526f>] [<a0010e5f>] [<a001d2ec>]
[<a012d637>] [<a017561e>] 
   [<a0010e5f>] [<a017561e>] [<a0010405>] [<a00103f1>]
[<a0010e5f>] [<a000d965>] 
   [<a017561e>] [<a0175616>] [<a00b26ec>] [<a00bd0d1>]
[<a0015e2f>] [<a00bd268>] 
   [<a00e1fc4>] [<a00b4caf>] [<a00e0057>] [<a00c32d5>]
[<a00b4caf>] [<a00c3a6a>] 
   [<a012f024>] [<a00c42e2>] [<a00b2816>] [<a00b2855>]
[<a00b277e>] [<a00c3035>] 
   [<a00c8bc0>] [<a001622f>] [<a001a8e3>] [<a0016153>]
[<a001607b>] [<a0016037>] 
   [<a00b26ec>] [<a0015de1>] [<a0015dcf>] [<a00ada41>]
[<a00ada52>] [<a00b3dfe>] 
   [<a00b4108>] [<a00bb278>] [<a00bb211>] [<a00bb211>]
[<a00bb278>] [<a00b4bed>] 
   [<a00b4ba8>] [<a012ef38>] [<a014639d>] [<a014639d>]
[<a012ef38>] [<a00c8db0>] 
   [<a00bb56e>] [<a00bb3e0>] [<a00bb7f0>] [<a00b0404>]
[<a00bb7f0>] [<a00bb304>] 
   [<a0053f2f>] [<a00bb64c>] [<a00ab920>] [<a00b0404>]
[<a00bb3d4>] [<a00c8c7b>] 
   [<a00bb304>] [<a00bb458>] [<a00bb59c>] [<a00bb64c>]
[<a012f024>] [<a00bb59c>] 
   [<a00bb3d4>] [<a00b0404>] [<a00bb64c>] [<a00bb458>]
[<a00bb59c>] [<a00bb59c>] 
   [<a00b597f>] [<a00b2855>] [<a00bb458>] [<a00be776>]
[<a00be776>] [<a00be81d>] 
   [<a0146380>] [<a00b0658>] [<a00be81d>] [<a00e031b>]
[<a00e05d6>] [<a00bb59c>] 
   [<a00e1458>] [<a00bb637>] [<a00e0057>] [<a00e0057>]
[<a00c3a29>] [<a00c32d5>] 
   [<a00c5f3d>] [<a00c5e11>] [<a00c0e91>] [<a00c5d50>]
[<a0033e1a>] [<a00bad8e>] 
   [<a00b35bb>] [<a00b36e3>] [<a00baddc>] [<a00badd3>]
[<a00b9fb5>] [<a00ba0bd>] 
   [<a00b01ba>] [<a00ba31a>] [<a00b26ec>] [<a00baa87>]
[<a00baa71>] [<a012ef38>] 
   [<a012efd1>] 



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[uml-devel] 2.4.27 guest bug reconfirmed Re bug report [ 745826 ] run cat /dev/urandom

[Struan Bartlett]

[-- Attachment #1: Type: text/plain, Size: 4203 bytes --]

I've now tested for this bug using a simplified methodology on the 
latest patched-versions of the host (2.4.27 and 2.6.8) and guest (2.4.27 
and 2.6.9).

_New methodology_

My Debian guest system raises two xterms at startup. On each I log in as 
root. On one, I enter:

while true; do echo >/dev/null; done

On the second, I enter:

cat /dev/urandom

The devastating symptom: within 5 seconds the guest kernel has paniced 
and exited with the message (below) "kernel BUG at sched.c:564!".

_Findings_

guest 2.6.9: patched with uml-2.6.9-bb2.patch.bz2 - I am pleased to say 
I have not so far been able to reproduce this bug on this configuration.

guest 2.4.27: patched with uml-2.4.27-bs1.patch and 
uml-patch-2.4.24-1base.patch - no change; this bug is readily 
reproducible and so IS NOT FIXED, regardless of whether the guest is run 
on host 2.4.27 or 2.6.8

_Conclusion_

If such a simple pair of commands as this causes such devastating 
consequences, it seems the 2.4.27 kernel sched.c line 564 needs to be 
taken a look at - unless, that is, Jeff Dike's recent post about 
uml-patch-2.4.27-1 "a nasty scheduler race fixed" addresses this bug.

Jeff: where can I get your uml-patch-2.4.27-1 ?

Struan

Struan Bartlett wrote:

> Posted to SourceForge:
>
> For the record, this is not entirely fixed. I'm running a Debian host
> with 2.4.25 kernel and host-skas3-2.4.25.patch, and a Debian
> guest with 2.4.27 kernel and uml-patch-2.4.26-3.
>
> In one xterm I ran "while true; do ls -la /dev/*; done" (see
> also bug report 617709). In the other, "cat /dev/urandom".
> After 5-10 seconds, the 'linux' host process crashes
> completely with:
>
> Scheduling in interrupt
> Kernel panic: kernel BUG at sched.c:564!
>
> In interrupt handler - not syncing
> <6>SysRq : Show Regs
>
> EIP: 0023:[<400e4b38>] CPU: 0 Not tainted ESP: 002b:bffffc68
> EFLAGS: 00000246
>    Not tainted
> EAX: ffffffda EBX: 00000001 ECX: 0804cdf0 EDX: 00001000
> ESI: 00001000 EDI: 0804cdf0 EBP: bffffc88 DS: 002b ES: 002b
> Call Trace: [<a0010e5f>] [<a00cae60>] [<a018db51>]
> [<a018dade>] [<a000dc93>]   [<a00cade9>] [<a00b526f>] [<a0010e5f>] 
> [<a001d2ec>]
> [<a012d637>] [<a017561e>]   [<a0010e5f>] [<a017561e>] [<a0010405>] 
> [<a00103f1>]
> [<a0010e5f>] [<a000d965>]   [<a017561e>] [<a0175616>] [<a00b26ec>] 
> [<a00bd0d1>]
> [<a0015e2f>] [<a00bd268>]   [<a00e1fc4>] [<a00b4caf>] [<a00e0057>] 
> [<a00c32d5>]
> [<a00b4caf>] [<a00c3a6a>]   [<a012f024>] [<a00c42e2>] [<a00b2816>] 
> [<a00b2855>]
> [<a00b277e>] [<a00c3035>]   [<a00c8bc0>] [<a001622f>] [<a001a8e3>] 
> [<a0016153>]
> [<a001607b>] [<a0016037>]   [<a00b26ec>] [<a0015de1>] [<a0015dcf>] 
> [<a00ada41>]
> [<a00ada52>] [<a00b3dfe>]   [<a00b4108>] [<a00bb278>] [<a00bb211>] 
> [<a00bb211>]
> [<a00bb278>] [<a00b4bed>]   [<a00b4ba8>] [<a012ef38>] [<a014639d>] 
> [<a014639d>]
> [<a012ef38>] [<a00c8db0>]   [<a00bb56e>] [<a00bb3e0>] [<a00bb7f0>] 
> [<a00b0404>]
> [<a00bb7f0>] [<a00bb304>]   [<a0053f2f>] [<a00bb64c>] [<a00ab920>] 
> [<a00b0404>]
> [<a00bb3d4>] [<a00c8c7b>]   [<a00bb304>] [<a00bb458>] [<a00bb59c>] 
> [<a00bb64c>]
> [<a012f024>] [<a00bb59c>]   [<a00bb3d4>] [<a00b0404>] [<a00bb64c>] 
> [<a00bb458>]
> [<a00bb59c>] [<a00bb59c>]   [<a00b597f>] [<a00b2855>] [<a00bb458>] 
> [<a00be776>]
> [<a00be776>] [<a00be81d>]   [<a0146380>] [<a00b0658>] [<a00be81d>] 
> [<a00e031b>]
> [<a00e05d6>] [<a00bb59c>]   [<a00e1458>] [<a00bb637>] [<a00e0057>] 
> [<a00e0057>]
> [<a00c3a29>] [<a00c32d5>]   [<a00c5f3d>] [<a00c5e11>] [<a00c0e91>] 
> [<a00c5d50>]
> [<a0033e1a>] [<a00bad8e>]   [<a00b35bb>] [<a00b36e3>] [<a00baddc>] 
> [<a00badd3>]
> [<a00b9fb5>] [<a00ba0bd>]   [<a00b01ba>] [<a00ba31a>] [<a00b26ec>] 
> [<a00baa87>]
> [<a00baa71>] [<a012ef38>]   [<a012efd1>]
>
>
> -------------------------------------------------------
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[-- Attachment #2: Type: text/html, Size: 6028 bytes --]

Re: [uml-devel] 2.4.27 guest bug reconfirmed Re bug report [ 745826 ] run cat /dev/urandom

[Blaisorblade]

On Sunday 14 November 2004 11:47, Struan Bartlett wrote:
> I've now tested for this bug using a simplified methodology on the
> latest patched-versions of the host (2.4.27 and 2.6.8) and guest (2.4.27
> and 2.6.9).

> _New methodology_

> My Debian guest system raises two xterms at startup. On each I log in as
> root. On one, I enter:

> while true; do echo >/dev/null; done

> On the second, I enter:

> cat /dev/urandom

> The devastating symptom: within 5 seconds the guest kernel has paniced
> and exited with the message (below) "kernel BUG at sched.c:564!".
>
> _Findings_

> guest 2.6.9: patched with uml-2.6.9-bb2.patch.bz2 - I am pleased to say
> I have not so far been able to reproduce this bug on this configuration.

> guest 2.4.27: patched with uml-2.4.27-bs1.patch and
> uml-patch-2.4.24-1base.patch - no change; this bug is readily
> reproducible and so IS NOT FIXED, regardless of whether the guest is run
> on host 2.4.27 or 2.6.8

> _Conclusion_
>
> If such a simple pair of commands as this causes such devastating
> consequences, it seems the 2.4.27 kernel sched.c line 564 needs to be
> taken a look at - unless, that is, Jeff Dike's recent post about
> uml-patch-2.4.27-1 "a nasty scheduler race fixed" addresses this bug.
I may be wrong, but I think I should have picked that patch into 2.4.27-bs1.

> Jeff: where can I get your uml-patch-2.4.27-1 ?
It's at http://user-mode-linux.sourceforge.net/dl-ists.html

I'll take a look at your report - there is one patch applied on 2.6 that 
seemed unneeded on 2.4 until now - this may be reconsidered...
> Struan

-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729



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uml-patch-2.4.27-1 not fixed Re: [uml-devel] 2.4.27 guest bug reconfirmed Re bug report [ 745826 ] run cat /dev/urandom

[Struan Bartlett]

[-- Attachment #1: Type: text/plain, Size: 1718 bytes --]

I've compiled and ran the test (below) on a virgin 2.4.27 kernel patched 
with uml-patch-2.4.27-1.bz2.

Result: the bug is still readily reproducible and _is not fixed_ in this 
patch.

P.S. Jeff Dike: if CONFIG_NETFILTER=y is set in .config, the patched 
kernel fails to compile.

Blaisorblade wrote:

>On Sunday 14 November 2004 11:47, Struan Bartlett wrote:
>  
>
>>I've now tested for this bug using a simplified methodology on the
>>latest patched-versions of the host (2.4.27 and 2.6.8) and guest (2.4.27
>>and 2.6.9).
>>    
>>
>>_New methodology_
>>    
>>
>>My Debian guest system raises two xterms at startup. On each I log in as
>>root. On one, I enter:
>>    
>>
>>while true; do echo >/dev/null; done
>>    
>>
>>On the second, I enter:
>>    
>>
>>cat /dev/urandom
>>    
>>
>>The devastating symptom: within 5 seconds the guest kernel has paniced
>>and exited with the message (below) "kernel BUG at sched.c:564!".
>>
>>_Findings_
>>    
>>
>>guest 2.4.27: patched with uml-2.4.27-bs1.patch and
>>uml-patch-2.4.24-1base.patch - no change; this bug is readily
>>reproducible and so IS NOT FIXED, regardless of whether the guest is run
>>on host 2.4.27 or 2.6.8
>>    
>>
>>_Conclusion_
>>
>>If such a simple pair of commands as this causes such devastating
>>consequences, it seems the 2.4.27 kernel sched.c line 564 needs to be
>>taken a look at - unless, that is, Jeff Dike's recent post about
>>uml-patch-2.4.27-1 "a nasty scheduler race fixed" addresses this bug.
>>    
>>
>I may be wrong, but I think I should have picked that patch into 2.4.27-bs1.
>
>I'll take a look at your report - there is one patch applied on 2.6 that 
>seemed unneeded on 2.4 until now - this may be reconsidered...
>  
>


[-- Attachment #2: Type: text/html, Size: 2643 bytes --]

Re: uml-patch-2.4.27-1 not fixed Re: [uml-devel] 2.4.27 guest bug reconfirmed Re bug report [ 745826 ] run cat /dev/urandom

[Blaisorblade]

On Tuesday 16 November 2004 16:44, Struan Bartlett wrote:
> I've compiled and ran the test (below) on a virgin 2.4.27 kernel patched
> with uml-patch-2.4.27-1.bz2.
>
> Result: the bug is still readily reproducible and _is not fixed_ in this
> patch.

> P.S. Jeff Dike: if CONFIG_NETFILTER=y is set in .config, the patched
> kernel fails to compile.
This one was probably just a "clean-to-fix" bug.

Ok, I have just one more clue now (not the solution yet). The first problem 
was that I went searching for "scheduler fixes" from 2.6: well, I merged some 
more, but without success. So, I've looked again at the infamous line 564, 
and what I realized (don't ask me why I missed this last time) is that this 
BUG line:

        if (unlikely(in_interrupt())) {
                printk("Scheduling in interrupt\n");
                BUG();
        }
is triggered because of a bug in the urandom driver - which you use in both 
your reproducing methods. So, we are down to some bug related to code in 
urandom.c; since it works in mainline, I think the problem probably lies in 
code managing interrupts and / or timing (since they are related to random 
numbers generation).

Btw, I just got the same panic by simply running "cat /dev/urandom"!

> >>cat /dev/urandom

> >>The devastating symptom: within 5 seconds the guest kernel has paniced
> >>and exited with the message (below) "kernel BUG at sched.c:564!".

> >>_Conclusion_
> >>
> >>If such a simple pair of commands as this causes such devastating
> >>consequences, it seems the 2.4.27 kernel sched.c line 564 needs to be
> >>taken a look at - unless, that is, Jeff Dike's recent post about
> >>uml-patch-2.4.27-1 "a nasty scheduler race fixed" addresses this bug.

-- 
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729
http://www.user-mode-linux.org/~blaisorblade




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