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On Thu, Mar 27, 2008 at 08:25:31PM -0700, Andrew Morton wrote: > On Tue, 25 Mar 2008 15:44:00 +0100 Rodolfo Giometti <giometti@enneenne.com> wrote: > > > > > > As it stands, there might be deadlocks such as when a process which itself > > > holds a ref on the pps_device (with an open fd?) calls > > > pps_unregister_source. > > > > I can add a wait_event_interruptible in order to allow userland to > > continue by receiving a signal. It could be acceptable? > > There should be no need to "wait" for anything. When the final reference > to an object is released, that object is cleaned up. Just like we do for > inodes, dentries, pages, files, and 100 other kernel objects. > > The need to wait for something else to go away is a big red flag with > "busted refcounting" written on it. > > > > Also, we need to take care that all processes which were waiting in > > > pps_unregister_source() get to finish their cleanup before we permit rmmod > > > to proceed. Is that handled somewhere? > > > > I don't understand the problem... this code as been added in order to > > avoid the case where a pps_event() is called while a process executes > > the pps_unregister_source(). If more processes try to execute this > > code the first which enters will execute idr_remove() which prevents > > another process to reach the wait_event()... is that wrong? =:-o > > I was asking you! > > We should get the reference counting and object lifetimes sorted out first. > There should be no "wait for <object> to be released" code. Once that is > in place, things like rmmod will also sort themselves out: it just won't be > possible to remove the module while there are live references to objects. The problem is related to serial and parallel clients. The PPS source related to a serial port (or a parallel one) uses the serial (or parallel) IRQ to get PPS timestamps and it could be possible that a process tries to close the PPS source while another CPU is runnig the serial IRQ, so I cannot remove the PPS object until the IRQ handler is finished its job on the PPS object. For clients (currently none :) which define their own IRQ handler for PPS timestamps managing the problem doesn't arise at all. Ciao, Rodolfo -- GNU/Linux Solutions e-mail: giometti@enneenne.com Linux Device Driver giometti@gnudd.com Embedded Systems giometti@linux.it UNIX programming phone: +39 349 2432127 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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