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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Qian Cai <cai@lca.pw>, Peter Zijlstra <peterz@infradead.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        X86 ML <x86@kernel.org>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Wei Liu <wei.liu@kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        Jason Chen CJ <jason.cj.chen@intel.com>,
        Zhao Yakui <yakui.zhao@intel.com>,
        Alexander Potapenko <glider@google.com>
Subject: Re: [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack
In-Reply-To: <20200605175200.GA5393@lca.pw>
References: <20200521200513.656533920@linutronix.de> <20200521202117.763775313@linutronix.de> <20200605171816.GA4259@lca.pw> <20200605173622.GL3976@hirez.programming.kicks-ass.net> <20200605175200.GA5393@lca.pw>
Date:   Sun, 07 Jun 2020 13:59:53 +0200
Message-ID: <87v9k3jdc6.fsf@nanos.tec.linutronix.de>
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CC:+ Alexander

Qian Cai <cai@lca.pw> writes:
> On Fri, Jun 05, 2020 at 07:36:22PM +0200, Peter Zijlstra wrote:
>> > [ 9371.959858]  asm_call_on_stack+0x12/0x20
>> > asm_call_on_stack at arch/x86/entry/entry_64.S:710
>
> This is one piece of call from the warning call traces that introduced
> by the patch which leads me to revert the commit in the first place. It
> may or may not be the real culprit, but just wanted to highlight it in
> case.

Oh well. The warning is a storage check in the stack depot code,
i.e. stack depot ran out of storage space.

Even if that commit causes stack traces to be larger that revert does
not make any sense at all and handwaving about recursions does not help
either. If that commit introduced a recursion then that would have worse
effects than triggering this warning.

The difference between the interrupt stack switching introduced by this
commit is that it generates another entry in the stack trace compared to
the state before it, which obviously has an effect on the storage
requirements in the stack depot.

Thanks,

        tglx