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cv=none; b=CC2qjGIFb5b95EKj1cbePf7gLub0liyW/oqW43Aoet09Gffc07PmAmaAz5fUjT3pqittgu I+axlQ4tHBIz7VU+Ea0dfhIDxdmEEsqjXkqQ8neR0WNz+7fMD1yfkZUlz98nT/TizdCoKy hCxuU75X3Z1lmFoHoS1EiIx90mXp6X0= Received: from omf03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 2DBF31AE85; Mon, 5 Jan 2026 21:40:17 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf03.hostedemail.com (Postfix) with ESMTPA id E27946000B; Mon, 5 Jan 2026 21:40:13 +0000 (UTC) Date: Mon, 5 Jan 2026 16:40:36 -0500 From: Steven Rostedt To: Vlastimil Babka Cc: Andrew Morton , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Sebastian Andrzej Siewior , Clark Williams , Mel Gorman , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, stable@vger.kernel.org, kernel test robot , Matthew Wilcox Subject: Re: [PATCH mm-hotfixes] mm/page_alloc: prevent pcp corruption with SMP=n Message-ID: <20260105164036.32a22c2e@gandalf.local.home> In-Reply-To: <20260105-fix-pcp-up-v1-1-5579662d2071@suse.cz> References: <20260105-fix-pcp-up-v1-1-5579662d2071@suse.cz> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX18uqG90fClQgYqM+gD7rF9u4JBB5PDylXs= X-HE-Meta: U2FsdGVkX18D8vhglud99GU7CXmQ3Vimslye/1+TjZjBXISc1kIieVs/XQKSr4g6+QlVr7/o2HccNhzJQETTMl/B3o7ZZ56IUoHf+eDzwZQpMU3U7Kxey0/E/eyNuopzOc9dYfGhezalTsrvwlIiLoSX4GAONhfUChSXPxSdcw1SQnIxlwxuhU2ylSOQB12csT3H+njuA4KavBrP7AnFflX+0Wzx3ckM6TQLMNk/Hg8irAcqYims6mxoijVg+8zN6RVMSh0T96rx17VrqsQCPD8gXu9HHDiVQaVi4wdFyYT8UtwbpxS2cd+aIawIEQ8o X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: DE26820005 X-Stat-Signature: 7nuqsgdj3h9hzx7tpa8ej48rkpshrfas X-HE-Tag-Orig: 1767649213-413291 X-HE-Tag: 1767649218-157167 X-HE-Meta: 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 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: List-Subscribe: List-Unsubscribe: On Mon, 05 Jan 2026 16:08:56 +0100 Vlastimil Babka wrote: > +++ b/mm/page_alloc.c > @@ -167,6 +167,31 @@ static inline void __pcp_trylock_noop(unsigned long *flags) { } > pcp_trylock_finish(UP_flags); \ > }) > > +/* > + * With the UP spinlock implementation, when we spin_lock(&pcp->lock) (for i.e. > + * a potentially remote cpu drain) and get interrupted by an operation that > + * attempts pcp_spin_trylock(), we can't rely on the trylock failure due to UP > + * spinlock assumptions making the trylock a no-op. So we have to turn that > + * spin_lock() to a spin_lock_irqsave(). This works because on UP there are no > + * remote cpu's so we can only be locking the only existing local one. > + */ > +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT) > +static inline void __flags_noop(unsigned long *flags) { } > +#define spin_lock_maybe_irqsave(lock, flags) \ > +({ \ > + __flags_noop(&(flags)); \ > + spin_lock(lock); \ > +}) > +#define spin_unlock_maybe_irqrestore(lock, flags) \ > +({ \ > + spin_unlock(lock); \ > + __flags_noop(&(flags)); \ > +}) > +#else > +#define spin_lock_maybe_irqsave(lock, flags) spin_lock_irqsave(lock, flags) > +#define spin_unlock_maybe_irqrestore(lock, flags) spin_unlock_irqrestore(lock, flags) > +#endif > + These are very generic looking names for something specific for page_alloc.c. Could you add a prefix of some kind to make it easy to see that these are specific to the mm code? mm_spin_lock_maybe_irqsave() ? Thanks, -- Steve