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Peter Anvin" , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Andy Lutomirski , Peter Zijlstra , "Paul E. McKenney" , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Josh Poimboeuf , Kees Cook , Sami Tolvanen , Ard Biesheuvel , Nicholas Piggin , Juerg Haefliger , Nicolas Saenz Julienne , "Kirill A. Shutemov" , Nadav Amit , Dan Carpenter , Chuang Wang , Yang Jihong , Petr Mladek , "Jason A. Donenfeld" , Song Liu , Julian Pidancet , Tom Lendacky , Dionna Glaze , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Juri Lelli , Daniel Bristot de Oliveira , Marcelo Tosatti , Yair Podemsky Subject: Re: [RFC PATCH 11/14] context-tracking: Introduce work deferral infrastructure Message-ID: References: <20230705181256.3539027-1-vschneid@redhat.com> <20230705181256.3539027-12-vschneid@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Queue-Id: 4230814000C X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: swnwfxwjienos4qs59n936zjydc8sofo X-HE-Tag: 1688644544-183125 X-HE-Meta: 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 9x2PbKdF 6clVim63mALtBnlnsfRMxIPHSIM0BGFosulYwukeTEro9fd3rZasWI0SuSqE3A12GgJi9w6ReCCzprRm95UTASSWgBRQ0PyQpReqxmyNBKixmbpLA27hgmXFlmFX46RkqTl5zPlQO6ElrnePXeCXagw6w4dYvTxJ7AVudbF4NJXeiViac7V2SkYfmqu+D43q1oZaYRugNkUV1hrPh9RxWgPbE6p8nJmEKsfYOX9Jdmvwd+OegU1pxQZ1C5p8+STjs7ggF97+bN0WVpekQzTFZ07SuoTS8hF3/sv62 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jul 06, 2023 at 12:23:57AM +0200, Frederic Weisbecker wrote: > Le Wed, Jul 05, 2023 at 07:12:53PM +0100, Valentin Schneider a écrit : > +bool ct_set_cpu_work(unsigned int cpu, unsigned int work) > +{ > + struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu); > + unsigned int old, new, state; > + bool ret = false; > + > + preempt_disable(); > + > + work <<= CONTEXT_WORK; > + state = atomic_read(&ct->state); > + /* > + * Try setting the work until either > + * - the target CPU is on the kernel > + * - the work has been set > + */ > + for (;;) { > + /* Only set if running in user/guest */ > + old = state; > + old &= ~CONTEXT_MASK; > + old |= CONTEXT_USER; > + > + new = old | work; > + > + state = atomic_cmpxchg(&ct->state, old, new); > + if (state & work) { And this should be "if (state == old)", otherwise there is a risk that someone else had set the work but atomic_cmpxchg() failed due to other modifications is the meantime. It's then dangerous in that case to defer the work because atomic_cmpxchg() failures don't imply full ordering. So there is a risk that the target executes the work but doesn't see the most recent data. Thanks.