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Date: Wed, 26 Sep 2001 22:08:13 -0700 (PDT)
From: Marcel Moolenaar <marcel@FreeBSD.org>
To: freebsd-gnats-submit@FreeBSD.org
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Subject: kern/30861: Linuxulator: stackgap does not handle recursion from interrupted syscalls.
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>Number:         30861
>Category:       kern
>Synopsis:       Linuxulator: stackgap does not handle recursion from interrupted syscalls.
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Sep 26 22:10:00 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator:     Marcel Moolenaar
>Release:        -current & -stable
>Organization:
FreeBSD
>Environment:
>Description:
Peter says:

Ever wonder why things crash for no apparent reason?  I think I know why.
 
Check out the stackgap_alloc() stuff.  Then think about linuxthreads
where multiple processes are using the same stack gap.  Think what happens
when one process does a translated syscall, blocks, and another one does
a syscall and reuses the same gap space. :-(

Solutions are ugly. :-(

Possible solution 1:
  make the stackgap_*() functions reentrant and alloc/free the space.
  downside: we presently have a small gap space and dont "free" the
  gap space.  We could run out of space easily.

Possible solution 2:
  Use space below the user stack.  We may have to do this.  This is nasty
  too, because we will have to assume that there is nothing below the
  user stack %esp.

Possible solution 3:
  Put a lock around stackgap functions so that translated syscalls are
  not reentrant.  This is really nasty as it single threads linuxthreads
  syscalls.

>How-To-Repeat:

>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:

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