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

[Struan Bartlett <struan@praguespringpeople.org>]

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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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