Date: Thu, 14 Aug 1997 21:05:26 +0200 From: Poul-Henning Kamp <phk@critter.dk.tfs.com> To: Steve Passe <smp@csn.net> Cc: Poul-Henning Kamp <phk@dk.tfs.com>, smp@freebsd.org Subject: Re: bug ? Message-ID: <3668.871585526@critter.dk.tfs.com> In-Reply-To: Your message of "Thu, 14 Aug 1997 12:05:09 MDT." <199708141805.MAA02086@Ilsa.StevesCafe.com>
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In message <199708141805.MAA02086@Ilsa.StevesCafe.com>, Steve Passe writes:
>Hi,
>
>>
>> this is from sys/kern/kern_lock.c, isn't line 76 & 77 bogus ?
>>
>> 64 | */
>> 65 | int lock_wait_time = 100;
>> 66 | #define PAUSE(lkp, wanted)
> \
>> 67 | if (lock_wait_time > 0) {
> \
>> 68 | int i;
> \
>> 69 |
> \
>> 70 | simple_unlock(&lkp->lk_interlock);
> \
>> 71 | for (i = lock_wait_time; i > 0; i--)
> \
>> 72 | if (!(wanted))
> \
>> 73 | break;
> \
>> 74 | simple_lock(&lkp->lk_interlock);
> \
>> 75 | }
> \
>> 76 | if (!(wanted))
> \
>> 77 | break;
>> 78 |
>> 79 | #else /* NCPUS == 1 */
>
>I think it's necessary. In a multiprocessor system there is a chance
>another CPU could grab the lock between lines 73 & 74. So line 76 is a
>test to guarantee that its still "!(wanted)" after re-acquiring the
>simple_lock. There is also the possibility that you timeout without getting
>"wanted", line 76 deals with this.
Ok, but what does the "break" break out of ?
That's where it looks bogus to me...
I also don't understand why you don't check at the top, but always
take a simple_unlock/simple_lock pair, even in the best case situation..
--
Poul-Henning Kamp | phk@FreeBSD.ORG FreeBSD Core-team.
http://www.freebsd.org/~phk | phk@login.dknet.dk Private mailbox.
whois: [PHK] | phk@tfs.com TRW Financial Systems, Inc.
Power and ignorance is a disgusting cocktail.
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