From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0714BC433F5 for ; Wed, 8 Sep 2021 02:56:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E4FCA60555 for ; Wed, 8 Sep 2021 02:56:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347404AbhIHC51 (ORCPT ); Tue, 7 Sep 2021 22:57:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:54150 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345895AbhIHC5R (ORCPT ); Tue, 7 Sep 2021 22:57:17 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2DAD261102; Wed, 8 Sep 2021 02:56:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1631069770; bh=JTuuKuBB4TF3mceLklzO/aQuRqCoA7/73JGLwJCc8PM=; h=Date:From:To:Subject:In-Reply-To:From; b=CbXFv+KqMrNxYBKK09e9xUNCHj0cxglAEasb/VAlxvvj/FkIx5VhrJhgvLBixprvm LR4upxhfUf9Maix7bO+aSoRs8OtN2j1Mmp9J7LYE8wltXTb5JtSDtMyj3lcBPrTOBU iwvP2r/HEiFGD5ezomaeyozLtXnI2O06wC90iwnc= Date: Tue, 07 Sep 2021 19:56:09 -0700 From: Andrew Morton To: akpm@linux-foundation.org, bigeasy@linutronix.de, linux-mm@kvack.org, mm-commits@vger.kernel.org, peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org, vbabka@suse.cz Subject: [patch 057/147] highmem: don't disable preemption on RT in kmap_atomic() Message-ID: <20210908025609.wt-dh5J3r%akpm@linux-foundation.org> In-Reply-To: <20210907195226.14b1d22a07c085b22968b933@linux-foundation.org> User-Agent: s-nail v14.8.16 Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org From: Sebastian Andrzej Siewior Subject: highmem: don't disable preemption on RT in kmap_atomic() kmap_atomic() disables preemption and pagefaults for historical reasons. The conversion to kmap_local(), which only disables migration, cannot be done wholesale because quite some call sites need to be updated to accommodate with the changed semantics. On PREEMPT_RT enabled kernels the kmap_atomic() semantics are problematic due to the implicit disabling of preemption which makes it impossible to acquire 'sleeping' spinlocks within the kmap atomic sections. PREEMPT_RT replaces the preempt_disable() with a migrate_disable() for more than a decade. It could be argued that this is a justification to do this unconditionally, but PREEMPT_RT covers only a limited number of architectures and it disables some functionality which limits the coverage further. Limit the replacement to PREEMPT_RT for now. Link: https://lkml.kernel.org/r/20210810091116.pocdmaatdcogvdso@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Acked-by: Vlastimil Babka Cc: Thomas Gleixner Cc: Peter Zijlstra Signed-off-by: Andrew Morton --- include/linux/highmem-internal.h | 27 ++++++++++++++++++++++----- 1 file changed, 22 insertions(+), 5 deletions(-) --- a/include/linux/highmem-internal.h~highmem-dont-disable-preemption-on-rt-in-kmap_atomic +++ a/include/linux/highmem-internal.h @@ -90,7 +90,11 @@ static inline void __kunmap_local(void * static inline void *kmap_atomic_prot(struct page *page, pgprot_t prot) { - preempt_disable(); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + migrate_disable(); + else + preempt_disable(); + pagefault_disable(); return __kmap_local_page_prot(page, prot); } @@ -102,7 +106,11 @@ static inline void *kmap_atomic(struct p static inline void *kmap_atomic_pfn(unsigned long pfn) { - preempt_disable(); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + migrate_disable(); + else + preempt_disable(); + pagefault_disable(); return __kmap_local_pfn_prot(pfn, kmap_prot); } @@ -111,7 +119,10 @@ static inline void __kunmap_atomic(void { kunmap_local_indexed(addr); pagefault_enable(); - preempt_enable(); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + migrate_enable(); + else + preempt_enable(); } unsigned int __nr_free_highpages(void); @@ -179,7 +190,10 @@ static inline void __kunmap_local(void * static inline void *kmap_atomic(struct page *page) { - preempt_disable(); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + migrate_disable(); + else + preempt_disable(); pagefault_disable(); return page_address(page); } @@ -200,7 +214,10 @@ static inline void __kunmap_atomic(void kunmap_flush_on_unmap(addr); #endif pagefault_enable(); - preempt_enable(); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + migrate_enable(); + else + preempt_enable(); } static inline unsigned int nr_free_highpages(void) { return 0; } _