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From: Jiri Slaby <>
To: Cyrill Gorcunov <>
Cc: Paul Gortmaker <>,
	LKML <>, Andi Kleen <>,
	Alexey Dobriyan <>
Subject: Re: [PATCH] driver: ip27-rtc - convert ioctl to unlocked_ioctl
Date: Mon, 14 Jan 2008 16:59:22 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20080114153806.GA6639@cvg>

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).

  reply	other threads:[~2008-01-14 16:00 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-13 20:32 [PATCH] driver: ip27-rtc - convert ioctl to unlocked_ioctl Cyrill Gorcunov
2008-01-13 21:07 ` Alexey Dobriyan
2008-01-13 21:25   ` Cyrill Gorcunov
2008-01-13 21:22 ` Jiri Slaby
2008-01-13 21:29   ` Jiri Slaby
2008-01-13 21:32     ` Cyrill Gorcunov
2008-01-14  6:38       ` Cyrill Gorcunov
2008-01-14 15:14         ` Jiri Slaby
2008-01-14 15:38           ` Cyrill Gorcunov
2008-01-14 15:59             ` Jiri Slaby [this message]
2008-01-14 16:07               ` Cyrill Gorcunov
2008-01-14 16:27                 ` Jiri Slaby
2008-01-14 16:28                   ` Cyrill Gorcunov
2008-01-13 23:08 ` Andi Kleen

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