lkml.org 
[lkml]   [2005]   [Dec]   [16]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
/
DateFri, 16 Dec 2005 17:00:09 -0800 (PST)
FromLinus Torvalds <>
SubjectRe: [PATCH 1/19] MUTEX: Introduce simple mutex implementation

On Fri, 16 Dec 2005, Joe Korty wrote:
> 
> The Mars Pathfinder incident is sufficient proof that some solution to
> the priority inversion problem is required in real systems.

Ehh. 

The Mars Pathfinder is just about the worst case "real system", and if I 
recall correctly, the reason it was able to continue was _not_ because it 
handled priority inversion, but because it reset itself every 24 hours or 
something like that, and had debugging facilities..

The _real_ lesson you should take away from it is not that priority 
inheritance is a good solution to priority inversion, but that having a 
failsafe switch when everthing goes wrong is critical. You don't know 
_what_ bug you'll encounter.

The bug itself could have been solved without priority inheritance, 
although I think in this case enabling that in VxWorks was the particular 
solution to the problem as being the least invasive.

Personally, I don't care what user space does. If some app wants to use 
priority inheritance to solve its bugs, that's fine. But it's like 
recursive locks: it's generally a _bandaid_ for bad locking. I definitely 
don't want the kernel depending on either.

So put a watchdog on your critical systems, and make sure you can debug 
them. Especially if they're on Mars.

			Linus
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-12-17 02:03    [from the cache]
©2003-2008