Re: [uml-devel] Re: tls: set_thread_area failed

[Blaisorblade <blaisorblade@yahoo.it>]

On Wednesday 14 December 2005 04:05, Sven Köhler wrote:
> > e2fsprogs-1.38/misc/fsck.c:check_all() repeatedly invokes fsck_device(),
> > which invokes execute(), which does a perfectly normal fork()/exec().
> > No threads here. Nor is there use of aio_*(), which might use threads
> > (well, POSIX allows it).
>
> Sorry, and what's the conclusion?
>
> fork() calles set_thread_area()?

Interesting... yep, it could.

Ok, picture down:

a) in NPTL, getpid() caches the result of the syscall in the TLS - so each new 
process at startup (i.e. after exec!) calls set_thread_area(). But that's 
normal.

b) I know that in clone()*, and I presume that in fork(), the pid cache must 
be invalidated / updated. So while fork() maybe doesn't use set_thread_area 
(and it could, seeing that no TLS setup has been done, and retrying) it wants 
to puzzle with the TLS content.

* We know that as glibc once didn't and UML was the one user of clone() + 
getpid(), and we discovered the hard way that glibc forgot that. Workarounded 
with a real getpid().

At bug report time we got an angry Ulrich saying "it's already fixed in latest 
version", luckily.
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

		
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