linux-kernel - Re: X86_64 BUG: missing FS/GS LDT reload on fork()

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Message-ID: <20100423230121.GA4563@const.famille.thibault.fr>
Date:	Sat, 24 Apr 2010 01:01:21 +0200
From:	Samuel Thibault <samuel.thibault@...ia.fr>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	olivier.aumage@...ia.fr, yannick.martin@...ia.fr
Subject: Re: X86_64 BUG: missing FS/GS LDT reload on fork()

Hello,

H. Peter Anvin, le Fri 23 Apr 2010 11:01:05 -0700, a écrit :
> On 04/23/2010 10:04 AM, Samuel Thibault wrote:
> > I have an issue with FS/GS LDT reload in the child of fork(). The
> > attached testcase fails quite often.  It sets an LDT entry up, uses
> > prctl to set gs's base to a 64bit value, then loads gs with the LDT
> > entry. The LDT entry is now in effect. After a fork call, the LDT entry
> > is not in effect any more, the 64bit base is back!
> 
> Okay... I have to say that I'm more than a bit confused why you're doing
> this,

:D

I'm fixing a user-level thread library with TLS support.

> The following patch looks like it should address that.

Indeed, it fixes the issue here.

Samuel
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