Messages in this thread | | | Date | Mon, 14 Jan 2008 16:59:22 +0100 | From | Jiri Slaby <> | Subject | Re: [PATCH] driver: ip27-rtc - convert ioctl to unlocked_ioctl |
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On 01/14/2008 04:38 PM, Cyrill Gorcunov wrote: > Jiri, I mean rtc_open() is protected by spinlock+status from being > opened simultaneously by a few processes. *But* lets imagine the > following situation - this fd (file descriptor) is opened by one > multithreaded application so all threads have an access to this > fd. Then one thread reads rtc periodically thru unlocked_ioctl > and another thread set new time from time to time. So the question > I have - is it possible to get second thread stopped at attemption to > get rtc spinlock while another thread is setting the new time? Or > this situation never-ever could be? i'm not really familiar with > process management in Linux and as result could be wrong.
Access to global variable 'rtc' (the rtc itself) is serialized through the spinlock, I see no problem there. If you call read-read-write-read from 4 tasks in userspace, it might be _still_ (no change) reordered to e.g. write-read-read-read by the scheduler.
In fact, the reading process is stopped while the another one is writing the time (due to spinlock).
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