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List: freebsd-security
Subject: Re: signal handling in urandom can cause lockup
From: Bruce Evans <bde () zeta ! org ! au>
Date: 1999-01-28 2:22:06
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> This is very interesting. For some time (I use FreeBSD on my
>desktop as well as for 50 odd servers) my desktop machine has been
>exhibiting a freeze that seems to coinside with intense swapping or
>writing to the disk. This 'freeze' survived the upgrade from 2.2.7 to
>3.0.
> Now... my take on the situation had been that IDE is just
>evil. I have burned out 3 drives (of different brands) in as many
>months (they ranged from 1 month to 1 year old). I have on order a 9G
>SCSI drive to become the main system and swap drive under the
>assumption that scsi drives are going to be more dependable and will
>not freeze the system.
I have no problems with IDE, and this problem has very little to do with
IDE. It is a general problem with devices that can transfer large amounts
of data without blocking (not just with slow devices like I said before,
except faster devices tend to limit the denial of service to a second
or two). E.g., a modern IDE drive can transfer at a rate of 12-15MB/sec.
The default interface is 16-bit PIO mode 1-4 (where the BIOS decides the
mode number). At best, this transfers data at 8.3MB/sec and takes 100%
of the CPU to do so. Don't connect a modern IDE drive to this interface.
> However, it does strike me as bogus that this kind of blocking
>happens. Maybe this type of patch should be applied to devices in
>general.
It already applies to everything that calls uiomove(), including many
cases involving filesystem i/o. It doesn't apply to paging or certain
optimised filesystem i/o.
Bruce
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