linux-kernel - Re: [PATCH] x86 tls prevent_tail

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Date:	Tue, 26 Feb 2008 23:38:21 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Tomasz Grobelny <tomasz@...belny.oswiecenia.net>
Subject: Re: [PATCH] x86 tls prevent_tail_call

> i'm wondering, have you seen this happen in practice? We use 
> sys_set_thread_area() for every new task started up. I guess we havent 
> seen problems in the field yet because this early during startup tasks 
> do not normally receive signals? (or if they do they are fatal and no 
> user signal context is used.)

Tomasz saw it.  I don't know what compiler or exact options to it he used.

> btw., this whole thing of us having to notice such tail-optimization 
> incidents is totally fragile and unreliable. Shouldnt there be a "dont 
> tail-optimize me" attribute which we could stick into asmlinkage? 

I agree.  It's come up before.  I'll talk to compiler folks about it again.

> Perhaps sparse could detect asmlinkage functions that do not do 
> prevent_tail_call()s?

That sounds like a good idea to me.


Thanks,
Roland

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