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Date:   Mon, 16 Oct 2023 18:55:41 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc:     Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Dario Faggioli <dfaggioli@suse.com>,
        Mike Rapoport <rppt@kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        marcelo.cerri@canonical.com, tim.gardner@canonical.com,
        philip.cox@canonical.com, aarcange@redhat.com, peterx@redhat.com,
        x86@kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        stable@kernel.org, Nikolay Borisov <nik.borisov@suse.com>
Subject: Re: [PATCHv2] efi/unaccepted: Fix soft lockups caused by parallel
 memory acceptance
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References: <20231016163122.12855-1-kirill.shutemov@linux.intel.com>
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On Mon, Oct 16, 2023 at 07:31:22PM +0300, Kirill A. Shutemov wrote:
>   v2:
>    - Fix deadlock (Vlastimil);
>    - Fix comments (Vlastimil);
>    - s/cond_resched()/cpu_relax()/ -- cond_resched() cannot be called
>      from atomic context;

Isn't there an implicit cpu_relax() while we're spinning?  Does this
really accomplish anything?

> +retry:
>  	spin_lock_irqsave(&unaccepted_memory_lock, flags);
[...]
> +		spin_unlock_irqrestore(&unaccepted_memory_lock, flags);
> +
> +		/*
> +		 * The code is reachable from atomic context.
> +		 * cond_resched() cannot be used.
> +		 */
> +		cpu_relax();
> +
> +		goto retry;