linux-kernel - Re: [PATCH 5.15 000/923] 5.15.3-rc3 review

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Message-ID: <20211118080627.GH174703@worktop.programming.kicks-ass.net>
Date:   Thu, 18 Nov 2021 09:06:27 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Holger Hoffstätte 
        <holger@...lied-asynchrony.com>,
        Qi Zheng <zhengqi.arch@...edance.com>,
        Kees Cook <keescook@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Justin Forbes <jmforbes@...uxtx.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Shuah Khan <shuah@...nel.org>, patches@...nelci.org,
        lkft-triage@...ts.linaro.org, Pavel Machek <pavel@...x.de>,
        Jon Hunter <jonathanh@...dia.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        stable <stable@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 5.15 000/923] 5.15.3-rc3 review

On Wed, Nov 17, 2021 at 03:50:17PM -0800, Linus Torvalds wrote:

> I really don't think the WCHAN code should use unwinders at all. It's
> too damn fragile, and it's too easily triggered from user space.

On x86, esp. with ORC, it pretty much has to. The thing is, the ORC
unwinder has been very stable so far. I'm guessing there's some really
stupid thing going on, like for example trying to unwind a freed stack.

I *just* managed to reproduce, so let me go have a poke.

> So I think we need to revert all the wchan changes. Not just in
> stable, but in mainline too.

Sure, we can do that. Want a pull request for that or will you just kill
them outright?