[LITMUS^RT] Modifying Page Table Entry in gsnedf_schedule()

[Namhoon Kim]

Hi All,

I'd like to modify page permissions to invoke a page fault. So, I used
set_pte() with modified pte access bits in gsnedf_schedule() . According to
kernel documentation (https://www.kernel.org/doc/Documentation/cachetlb.txt),
I should call flush_cache_page() before set_pte() and call flush_tlb_page()
after set_pte(). But, when I run several rtspin tasks, the following
warning messages are shown.

3194 P0 [vprintk_emit at kernel/printk.c:1564]: 4------------[ cut here
]------------
3195 P0 [vprintk_emit at kernel/printk.c:1564]: 4WARNING: at kernel/smp.c:244
smp_call_function_single+0x12f/0x190()
3196 P0 [vprintk_emit at kernel/printk.c:1564]: dModules linked in:3197 P0
[vprintk_emit at kernel/printk.c:1564]:
3198 P0 [vprintk_emit at kernel/printk.c:1564]: dCPU: 0 PID: 0 Comm: swapper/0
Tainted: G        W    3.10.5-kvm-test-pagefault #223
3199 P0 [vprintk_emit at kernel/printk.c:1564]: dHardware name:  , BIOS QEMU
01/01/2007
~~~(stack traces)

The codes at kernel/smp.c:244: (
https://github.com/LITMUS-RT/litmus-rt/blob/master/kernel/smp.c#L243)

*/*** * Can deadlock when called with interrupts disabled.** * We
allow cpu's that are not yet online though, as no one else can** *
send smp call function interrupt to this cpu and as such deadlocks** *
can't happen.** */*
 WARN_ON_ONCE <http://lxr.free-electrons.com/ident?v=3.10;i=WARN_ON_ONCE>(cpu_online
<http://lxr.free-electrons.com/ident?v=3.10;i=cpu_online>(this_cpu) &&
irqs_disabled <http://lxr.free-electrons.com/ident?v=3.10;i=irqs_disabled>()
                && !oops_in_progress
<http://lxr.free-electrons.com/ident?v=3.10;i=oops_in_progress>);

Are interrupts disabled when we enter gsnedf_schedule()? Does anyone know
how to modify page access bits in schedule() properly?

Thanks,

Namhoon Kim
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