Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757795AbaLJOZD (ORCPT ); Wed, 10 Dec 2014 09:25:03 -0500 Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:38080 "EHLO e06smtp14.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757533AbaLJOXo (ORCPT ); Wed, 10 Dec 2014 09:23:44 -0500 From: David Hildenbrand To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org Cc: benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, heiko.carstens@de.ibm.com, dahi@linux.vnet.ibm.com, schwidefsky@de.ibm.com, borntraeger@de.ibm.com, mst@redhat.com, tglx@linutronix.de, David.Laight@ACULAB.COM, peterz@infradead.org, hughd@google.com, hocko@suse.cz Subject: [PATCH v2 2/5] uaccess: count pagefault_disable() levels in pagefault_count Date: Wed, 10 Dec 2014 15:23:31 +0100 Message-Id: <1418221414-60110-3-git-send-email-dahi@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.5.5 In-Reply-To: <1418221414-60110-1-git-send-email-dahi@linux.vnet.ibm.com> References: <1418221414-60110-1-git-send-email-dahi@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14121014-0017-0000-0000-0000022862FF Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org pagefault_disable() and pagefault_enable() have to increment/decrement the pagefault_count. We keep manipulating the preempt count to retain compability to existing pagefault handlers. This has to be demangled in separate patches. It is now possible to verify whether in a pagefault_disable() envionment by calling pagefault_disabled(). Signed-off-by: David Hildenbrand --- include/linux/uaccess.h | 45 ++++++++++++++++++++++++++++++++++++++------- 1 file changed, 38 insertions(+), 7 deletions(-) diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index ecd3319..1dfc678 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -2,20 +2,45 @@ #define __LINUX_UACCESS_H__ #include +#include #include +static __always_inline int pagefault_count(void) +{ + return current_thread_info()->pagefault_count; +} + +static __always_inline int *pagefault_count_ptr(void) +{ + return ¤t_thread_info()->pagefault_count; +} + +static __always_inline void pagefault_count_inc(void) +{ + (*pagefault_count_ptr())++; +} + +static __always_inline void pagefault_count_dec(void) +{ + (*pagefault_count_ptr())--; +} + /* - * These routines enable/disable the pagefault handler in that - * it will not take any locks and go straight to the fixup table. + * These routines enable/disable the pagefault handler. If disabled, it will + * not take any locks and go straight to the fixup table. + * + * We increase the preempt and the pagefault count, to be able to distinguish + * whether we run in simple atomic context or in a real pagefault_disable() + * context. + * + * For now, after pagefault_disabled() has been called, we run in atomic + * context. User access methods will not sleep. * - * They have great resemblance to the preempt_disable/enable calls - * and in fact they are identical; this is because currently there is - * no other way to make the pagefault handlers do this. So we do - * disable preemption but we don't necessarily care about that. */ static inline void pagefault_disable(void) { preempt_count_inc(); + pagefault_count_inc(); /* * make sure to have issued the store before a pagefault * can hit. @@ -25,18 +50,24 @@ static inline void pagefault_disable(void) static inline void pagefault_enable(void) { -#ifndef CONFIG_PREEMPT /* * make sure to issue those last loads/stores before enabling * the pagefault handler again. */ barrier(); + pagefault_count_dec(); +#ifndef CONFIG_PREEMPT preempt_count_dec(); #else preempt_enable(); #endif } +/* + * Is the pagefault handler disabled? If so, user access methods will not sleep. + */ +#define pagefault_disabled() (pagefault_count() != 0) + #ifndef ARCH_HAS_NOCACHE_UACCESS static inline unsigned long __copy_from_user_inatomic_nocache(void *to, -- 1.8.5.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/