On 02/02/2012 01:53 AM, Mitchell Tasman wrote:
Xenomai documents rtdm_nrtsig_pend() as follows:
The signal handler will run in soft-IRQ context of the non-real-time
subsystem. Note the implications of this context, e.g. no invocation
of blocking operations.
As a result, I would have anticipated that when invoked from within the
signal handler, in_irq() would return 0, while in_softirq() would return
non-zero.
Actually, nrt_sig runs on behalf of a virtual interrupt, which is a hard
IRQ context from Linux's standpoint.
Instead, I've found that in_irq() returns the value 0x10000, which
(digging around in include/linux/hardirq.h) indicates that the hardirq
count is 1.
A partial Linux kernel stack backtrace, leading up to execution of the
signal handler, is as follows:
[ 217.844177] [<bf031838>] (my_signalClient+0x24/0x48
[my_rtdm_driver]) from [<c00df42c>] (__ipipe_sync_stage+0x164/0x198)
[ 217.844207] [<c00df42c>] (__ipipe_sync_stage+0x164/0x198) from
[<c0058960>] (ipipe_trigger_irq+0x14/0x20)
[ 217.844238] [<c0058960>] (ipipe_trigger_irq+0x14/0x20) from
[<c011ca78>] (gatekeeper_thread+0x1ac/0x398)
It seems that there are at least several possibilities:
1. I've misunderstood the documentation, and the signal handler is
intended to run in Linux hardirq context. If so, and I need softirq
context, I'd need to schedule a tasklet from within the signal handler.
2. There's something broken about my specific environment. I am
presently using a Beagleboard xM Rev C, running a TI 2.6.37-derived OMAP
kernel from the staging tree on Arago, with a tailored (by me) version
of the ARM I-pipe patchset for 2.6.37.6 that ships with Xenomai-2.6.0.
The Xenomai version is also the as-released 2.6.0.
3. I've discovered a bug (or feature) in the rtdm_nrtsig_pend()
implementation and/or in the underlying plumbing.
Perhaps someone from the Xenomai community can comment.
Thanks much.
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--
Philippe.
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