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Message-ID: <ZS15HZqK4hu5NjSh@casper.infradead.org>
Date: Mon, 16 Oct 2023 18:55:41 +0100
From: Matthew Wilcox <willy@...radead.org>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
Dave Hansen <dave.hansen@...el.com>,
Sean Christopherson <seanjc@...gle.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Joerg Roedel <jroedel@...e.de>,
Ard Biesheuvel <ardb@...nel.org>,
Andi Kleen <ak@...ux.intel.com>,
Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com>,
David Rientjes <rientjes@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Tom Lendacky <thomas.lendacky@....com>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Ingo Molnar <mingo@...hat.com>,
Dario Faggioli <dfaggioli@...e.com>,
Mike Rapoport <rppt@...nel.org>,
David Hildenbrand <david@...hat.com>,
Mel Gorman <mgorman@...hsingularity.net>,
marcelo.cerri@...onical.com, tim.gardner@...onical.com,
philip.cox@...onical.com, aarcange@...hat.com, peterx@...hat.com,
x86@...nel.org, linux-mm@...ck.org, linux-coco@...ts.linux.dev,
linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
stable@...nel.org, Nikolay Borisov <nik.borisov@...e.com>
Subject: Re: [PATCHv2] efi/unaccepted: Fix soft lockups caused by parallel
memory acceptance
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;
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