From: Davide Libenzi <davidel@xmailserver.org>
To: "Peter T. Breuer" <ptb@it.uc3m.es>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: recursive spinlocks. Shoot.
Date: Sun, 18 May 2003 16:26:26 -0700 (PDT) [thread overview]
Message-ID: <Pine.LNX.4.55.0305181623320.3568@bigblue.dev.mcafeelabs.com> (raw)
In-Reply-To: <200305182315.h4INFG428386@oboe.it.uc3m.es>
On Mon, 19 May 2003, Peter T. Breuer wrote:
> No. This is not true. Imagine two threads, timed as follows ...
>
> .
> .
> .
> .
> if ((snl)->uniq == current) {
> atomic_inc(&(snl)->count); .
> } else { .
> spin_lock(&(snl)->lock); .
> atomic_inc(&(snl)->count); .
> (snl)->uniq = current; <-> if ((snl)->uniq == current) {
> atomic_inc(&(snl)->count);
> } else {
> spin_lock(&(snl)->lock);
> atomic_inc(&(snl)->count);
> (snl)->uniq = current;
>
>
> There you are. One hits the read exactly at the time the other does a
> write. Bang.
So, what's bang for you ? The second task (the one that reads "uniq")
will either see "uniq" as NULL or as (task1)->current. And it'll go
acquiring the lock, as expected. Check it again ...
- Davide
next prev parent reply other threads:[~2003-05-18 23:14 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20030518202013$5297@gated-at.bofh.it>
2003-05-18 23:15 ` Peter T. Breuer
2003-05-18 23:26 ` Davide Libenzi [this message]
2003-05-19 12:48 ` Peter T. Breuer
2003-05-19 17:15 ` Davide Libenzi
2003-05-19 17:27 ` Peter T. Breuer
2003-05-19 17:57 ` Alan Cox
2003-05-19 19:51 ` Peter T. Breuer
2003-05-19 20:22 ` Robert White
[not found] <20030520231013$3d77@gated-at.bofh.it>
2003-05-21 14:16 ` Peter T. Breuer
[not found] <20030518182010$0541@gated-at.bofh.it>
2003-05-18 19:09 ` Peter T. Breuer
2003-05-18 19:31 ` Davide Libenzi
2003-05-18 19:49 ` Peter T. Breuer
2003-05-18 20:13 ` Davide Libenzi
2003-05-19 20:47 ` Jan Hudec
2003-05-18 9:21 Peter T. Breuer
2003-05-18 16:30 ` Martin J. Bligh
2003-05-18 16:35 ` William Lee Irwin III
2003-05-18 16:49 ` Arjan van de Ven
2003-05-18 16:54 ` William Lee Irwin III
2003-05-18 17:14 ` Martin J. Bligh
2003-05-18 17:24 ` Peter T. Breuer
2003-05-18 22:34 ` David Woodhouse
2003-05-19 13:37 ` Peter T. Breuer
2003-05-19 13:45 ` Jens Axboe
2003-05-19 13:47 ` Arjan van de Ven
[not found] ` <mailman.1053352200.24653.linux-kernel2news@redhat.com>
2003-05-19 23:54 ` Pete Zaitcev
2003-05-20 0:03 ` viro
2003-05-20 0:03 ` Johannes Erdfelt
2003-05-20 3:12 ` Robert White
2003-05-20 11:59 ` Helge Hafting
2003-05-20 12:23 ` Richard B. Johnson
2003-05-20 21:05 ` Robert White
2003-05-20 21:42 ` Richard B. Johnson
2003-05-20 23:06 ` Robert White
2003-05-21 14:01 ` Richard B. Johnson
2003-05-21 21:56 ` Robert White
2003-05-22 0:13 ` viro
2003-05-22 0:32 ` Robert White
2003-05-22 0:46 ` Carl-Daniel Hailfinger
2003-05-21 5:48 ` Nikita Danilov
2003-05-22 1:00 ` Rik van Riel
2003-05-22 3:11 ` Robert White
2003-05-22 4:04 ` Nick Piggin
2003-05-22 4:42 ` Peter T. Breuer
2003-05-22 5:09 ` Nick Piggin
2003-05-23 0:19 ` Robert White
2003-05-23 7:22 ` Nikita Danilov
2003-05-23 9:07 ` Helge Hafting
2003-05-23 12:18 ` William Lee Irwin III
2003-05-24 2:39 ` Robert White
2003-05-28 16:50 ` Timothy Miller
2003-05-19 2:05 ` Kevin O'Connor
2003-05-19 6:19 ` Jan Hudec
2003-05-19 10:29 ` Helge Hafting
2003-05-19 11:37 ` Nikita Danilov
2003-05-22 1:21 ` Daniel Phillips
2003-05-19 14:28 ` Martin J. Bligh
2003-05-18 18:13 ` Davide Libenzi
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