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From: Doug Ambrisko <ambrisko@ambrisko.com>
Message-Id: <200404042021.i34KLcVT039830@ambrisko.com>
In-Reply-To: <1839.1081109842@critter.freebsd.dk>
To: Poul-Henning Kamp <phk@phk.freebsd.dk>
Date: Sun, 4 Apr 2004 13:21:38 -0700 (PDT)
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cc: =?ISO-8859-1?Q?S=F8ren_Schmidt?= <sos@DeepCore.dk>
Subject: Re: Intel SATA ICH5/5R 6300ESB support patches
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Poul-Henning Kamp writes:
| In message <200404042002.i34K2nop038808@ambrisko.com>, Doug Ambrisko writes:
| >Søren Schmidt writes:
| 
| >| > I put in a patch for geom for bio_taskqueue_remove.  Since ata code
| >| > schedules bio_task it need to be cancelled when we abort and call
| >| > biodone.  If we don't cancel this task then when the task is 
| >| > run later we get a double free in UMA since we have cleaned up
| >| > twice and called biodone twice for the same request.
| 
| Sos@ forwarded that patch and it won't fly, it has no chance of
| working reliably on multi-cpu machines:
| 
| There is no guarantee that the task is still on the queue by the
| time you try to remove it, and if is not, it is likely to be because
| another CPU is already waiting for a lock in the ata driver in the
| bio_taskqueue handler function, so we have no way to cancel that
| other CPU's activity.
| 
| The correct solution is to not do the biodone when you cancel, but
| let the already scheduled bio_taskqueue event to do so.

Okay, I'll look at the ata code so that it only does it once.

Thanks,

Doug A.