lkml.org 
[lkml]   [2002]   [May]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: Segfault hidden in list.h
Date
I'm not hitting it, but I came across it while writing an application server
based on TUX 2.1.0. I noticed that Ingo didn't lock a list during reads. As
long as his code traverses forward (which it does) all is well. If, however,
some module writer out there fails to lock a list for reads and traverses
said list in reverse, a failure could result.

By logic design this assignment ordering eliminates the need for a read
lock, hence improving performance, not just data integrity.

Billy Rose
wrose@loislaw.com

> -----Original Message-----
> From: Jeff Garzik [mailto:jgarzik@mandrakesoft.com]
> Sent: Sunday, May 12, 2002 7:45 PM
> To: Rose, Billy
> Subject: Re: Segfault hidden in list.h
>
>
> Rose, Billy wrote:
>
> >The code inside of __list_add:
> >
> >next->prev = new;
> >new->next = next;
> >new->prev = prev;
> >pre-next = new;
> >
> >needs to be altered to:
> >
> >new->prev = prev;
> >new->next = next;
> >next->prev = new;
> >prev->next = new;
> >
> >If something is accessing the list in reverse at the time of
> insertion and
> >"next->prev = new;" has been executed, there exists a moment
> when new->prev
> >may contain garbage if the element had been used in another
> list and is
> >being transposed into a new one. Even if garbage is not
> present, and the
> >element had just been initialized (i.e. new->prev = new), a
> false list head
> >will appear briefly (from the executing thread's point of view).
> >
>
> It sounds like you need better locking, if you are hitting this...
>
>
-
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: 2005-03-22 13:26    [W:0.129 / U:0.200 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site