Re: [Regression] 2.6.24-git9: RT sched mishandles artswrapper (bisected)

On Friday, 1 of February 2008, Peter Zijlstra wrote:

On Fri, 2008-02-01 at 12:50 +0100, Rafael J. Wysocki wrote:
On Friday, 1 of February 2008, Peter Zijlstra wrote:

It arts run as root, or does it use RLIMIT_RTPRIO to allow users to
execute realtime tasks?

artswrapper is setuid root and RLIMIT_RTPRIO is apparently not used.
Still, artswrapper is running as a regular user, so it most probably drops
privileges early.

BTW, it fails while running the artsmessage utility used for displaying arts
error messages, so I guess there's an error in arts that this thing tries to
display and deadlocks (or something like that).

Should I test the patch nevertheless?

Don't think that would help any in this situation. The thing to look out
for are RT tasks running with a different uid than 0.

This patch would only stop a task from obtaining RT class scheduling
when already in a (misconfigured) group. If the task is RT and then
switches group another - similar - thing is needed.

Does this artsmessage thing also run with RT priority?

Well, it's in a strange state (after it's broken). From top:

PR = -51
NI = 0
S = R
%CPU = 0.0
%MEM = 0.0

Here's the corresponding trace from sysrq+t:

artswrapper R running task 5128 5776 1
ffff81007a8dbd88 0000000000000046 000000015c4321b0 ffff81006aa6e5c8
ffffffff806daa00 ffffffff806daa00 ffffffff806daa00 ffffffff806daa00
ffffffff806daa00 ffffffff806daa00 ffffffff806d7a60 ffffffff806daa00
Call Trace:
[<ffffffff8022fdb7>] ? try_to_wake_up+0x77/0x200
[<ffffffff8023573d>] __cond_resched+0x2d/0x60
[<ffffffff804ddce1>] _cond_resched+0x31/0x40
[<ffffffff804ddd24>] wait_for_common+0x34/0x170
[<ffffffff8022fdb7>] ? try_to_wake_up+0x77/0x200
[<ffffffff804ddec8>] wait_for_completion+0x18/0x20
[<ffffffff80235aba>] sched_exec+0xba/0xf0
[<ffffffff802b5a64>] do_execve+0x64/0x220
[<ffffffff802097c6>] sys_execve+0x46/0x70
[<ffffffff8020bab7>] stub_execve+0x67/0xb0
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