From: Davide Libenzi <davidel@xmailserver.org>
To: David Schwartz <davids@webmaster.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] udev enhancements to use kernel event queue
Date: Fri, 13 Jun 2003 08:44:59 -0700 (PDT) [thread overview]
Message-ID: <Pine.LNX.4.55.0306130834590.4201@bigblue.dev.mcafeelabs.com> (raw)
In-Reply-To: <MDEHLPKNGKAHNMBLJOLKCEFJDKAA.davids@webmaster.com>
On Fri, 13 Jun 2003, David Schwartz wrote:
> You could also do (in pseudo-code):
>
> top:
> ret <- v->counter
> inc ret
> LOCK incl v->counter
> cmp v->counter, ret
> jz end
> LOCK decl v->counter
> jmp top:
> end:
> return ret
>
> This does not strictly guarantee in order return values, but that's
> meaningless without a lock anyway.
It is even worse since it can return same values. Suppose counter is 0 :
TASK0 TASK1
top:
ret <- v->counter ; ret = 0
inc ret ; ret -> 1
LOCK incl v->counter ; counter -> 1
top:
ret <- v->counter ; ret = 1
inc ret ; ret -> 2
LOCK incl v->counter ; counter -> 2
cmp v->counter, ret ; match !! got 2
jz end
...
cmp v->counter, ret ; ret == 1 , counter == 2 no-match
jz end
LOCK decl v->counter ; counter -> 1
jmp top
Then TASK0 starts again with no interruption and gets 2. You need
instrucions that does atomic mod/cmp to do this kind of tricks.
- Davide
next prev parent reply other threads:[~2003-06-13 15:33 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-06-12 19:10 [PATCH] udev enhancements to use kernel event queue Steven Dake
2003-06-12 21:47 ` Patrick Mochel
2003-06-13 16:31 ` Steven Dake
2003-06-13 17:06 ` Patrick Mochel
2003-06-12 21:47 ` Greg KH
2003-06-12 22:03 ` Andrew Morton
2003-06-12 22:50 ` Greg KH
2003-06-12 22:51 ` Andrew Morton
2003-06-12 23:02 ` Greg KH
2003-06-12 23:09 ` Greg KH
2003-06-12 23:14 ` Patrick Mochel
2003-06-12 23:16 ` Robert Love
2003-06-12 23:25 ` Greg KH
2003-06-13 20:01 ` Oliver Neukum
2003-06-18 22:59 ` Greg KH
2003-06-19 0:12 ` Kevin P. Fleming
2003-06-19 0:20 ` Greg KH
2003-06-19 0:42 ` Kevin P. Fleming
2003-06-19 0:51 ` Greg KH
2003-06-19 0:25 ` Andrew Morton
2003-06-19 6:27 ` Oliver Neukum
2003-06-12 23:25 ` Patrick Mochel
2003-06-12 23:29 ` Robert Love
2003-06-12 23:32 ` Greg KH
2003-06-12 23:34 ` Patrick Mochel
2003-06-12 23:40 ` Paul Mackerras
2003-06-12 23:50 ` Robert Love
2003-06-13 12:44 ` Richard B. Johnson
2003-06-13 12:54 ` Olivier Galibert
2003-06-12 23:52 ` Patrick Mochel
2003-06-13 8:41 ` Alan Cox
2003-06-13 11:00 ` Paul Mackerras
2003-06-13 11:07 ` Herbert Xu
2003-06-13 13:31 ` Alan Cox
2003-06-13 19:57 ` Joe Korty
2003-06-13 21:10 ` Alan Cox
2003-06-13 11:17 ` David Schwartz
2003-06-13 15:44 ` Davide Libenzi [this message]
2003-06-12 23:42 ` Robert Love
2003-06-12 23:45 ` Davide Libenzi
2003-06-12 23:05 ` Robert Love
2003-06-19 19:51 ` Werner Almesberger
2003-06-26 12:17 ` Tommi Virtanen
2003-06-26 14:35 ` Werner Almesberger
2003-06-13 8:40 ` Alan Cox
2003-06-13 9:14 ` Olivier Galibert
2003-06-19 20:53 ` Werner Almesberger
2003-06-13 16:05 ` Steven Dake
2003-06-13 16:32 ` Greg KH
2003-06-13 15:51 ` Steven Dake
2003-06-13 16:41 ` Patrick Mochel
2003-06-13 16:42 ` Greg KH
2003-06-13 17:17 ` Chris Friesen
2003-06-12 22:27 ` Oliver Neukum
2003-06-13 16:03 ` Steven Dake
2003-06-13 16:50 ` Patrick Mochel
2003-06-13 17:10 ` Steven Dake
2003-06-13 18:26 ` Greg KH
2003-06-13 19:02 ` Patrick Mansfield
2003-06-13 17:32 ` Oliver Neukum
2003-06-13 18:23 ` Greg KH
2003-06-13 18:24 ` Greg KH
2003-06-13 7:17 ` Christoph Hellwig
2003-06-13 18:06 ` Linus Torvalds
2003-06-19 23:32 ` Werner Almesberger
2003-06-19 23:42 ` Steven Dake
2003-06-20 0:05 ` Linus Torvalds
2003-06-20 0:10 ` Steven Dake
2003-06-20 0:43 ` Linus Torvalds
2003-06-20 2:26 ` Werner Almesberger
2003-06-20 17:03 ` Steven Dake
2003-06-20 17:18 ` Patrick Mochel
2003-06-14 6:36 John Bradford
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