From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751911AbdK3IYI (ORCPT ); Thu, 30 Nov 2017 03:24:08 -0500 Received: from mx2.suse.de ([195.135.220.15]:41646 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750830AbdK3IYH (ORCPT ); Thu, 30 Nov 2017 03:24:07 -0500 Date: Thu, 30 Nov 2017 09:24:05 +0100 From: Michal Hocko To: Michael Kerrisk Cc: linux-api@vger.kernel.org, Khalid Aziz , Michael Ellerman , Andrew Morton , Russell King - ARM Linux , Andrea Arcangeli , linux-mm@kvack.org, LKML , linux-arch@vger.kernel.org, Florian Weimer , John Hubbard Subject: [PATCH v2] mmap.2: document new MAP_FIXED_SAFE flag Message-ID: <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> References: <20171129144219.22867-1-mhocko@kernel.org> <20171129144524.23518-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171129144524.23518-1-mhocko@kernel.org> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Updated version based on feedback from John. --- >>From ade1eba229b558431581448e7d7838f0e1fe2c49 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 29 Nov 2017 15:32:08 +0100 Subject: [PATCH] mmap.2: document new MAP_FIXED_SAFE flag 4.16+ kernels offer a new MAP_FIXED_SAFE flag which allows the caller to atomicaly probe for a given address range. [wording heavily updated by John Hubbard ] Signed-off-by: Michal Hocko --- man2/mmap.2 | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/man2/mmap.2 b/man2/mmap.2 index 385f3bfd5393..923bbb290875 100644 --- a/man2/mmap.2 +++ b/man2/mmap.2 @@ -225,6 +225,22 @@ will fail. Because requiring a fixed address for a mapping is less portable, the use of this option is discouraged. .TP +.BR MAP_FIXED_SAFE " (since Linux 4.16)" +Similar to MAP_FIXED with respect to the +.I +addr +enforcement, but different in that MAP_FIXED_SAFE never clobbers a pre-existing +mapped range. If the requested range would collide with an existing +mapping, then this call fails with +.B EEXIST. +This flag can therefore be used as a way to atomically (with respect to other +threads) attempt to map an address range: one thread will succeed; all others +will report failure. Please note that older kernels which do not recognize this +flag will typically (upon detecting a collision with a pre-existing mapping) +fall back a "non-MAP_FIXED" type of behavior: they will return an address that +is different than the requested one. Therefore, backward-compatible software +should check the returned address against the requested address. +.TP .B MAP_GROWSDOWN This flag is used for stacks. It indicates to the kernel virtual memory system that the mapping @@ -449,6 +465,12 @@ is not a valid file descriptor (and .B MAP_ANONYMOUS was not set). .TP +.B EEXIST +range covered by +.IR addr , +.IR length +is clashing with an existing mapping. +.TP .B EINVAL We don't like .IR addr , -- 2.15.0 -- Michal Hocko SUSE Labs From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: [PATCH v2] mmap.2: document new MAP_FIXED_SAFE flag Date: Thu, 30 Nov 2017 09:24:05 +0100 Message-ID: <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> References: <20171129144219.22867-1-mhocko@kernel.org> <20171129144524.23518-1-mhocko@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20171129144524.23518-1-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org To: Michael Kerrisk Cc: linux-api@vger.kernel.org, Khalid Aziz , Michael Ellerman , Andrew Morton , Russell King - ARM Linux , Andrea Arcangeli , linux-mm@kvack.org, LKML , linux-arch@vger.kernel.org, Florian Weimer , John Hubbard List-Id: linux-api@vger.kernel.org Updated version based on feedback from John. --- >>From ade1eba229b558431581448e7d7838f0e1fe2c49 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 29 Nov 2017 15:32:08 +0100 Subject: [PATCH] mmap.2: document new MAP_FIXED_SAFE flag 4.16+ kernels offer a new MAP_FIXED_SAFE flag which allows the caller to atomicaly probe for a given address range. [wording heavily updated by John Hubbard ] Signed-off-by: Michal Hocko --- man2/mmap.2 | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/man2/mmap.2 b/man2/mmap.2 index 385f3bfd5393..923bbb290875 100644 --- a/man2/mmap.2 +++ b/man2/mmap.2 @@ -225,6 +225,22 @@ will fail. Because requiring a fixed address for a mapping is less portable, the use of this option is discouraged. .TP +.BR MAP_FIXED_SAFE " (since Linux 4.16)" +Similar to MAP_FIXED with respect to the +.I +addr +enforcement, but different in that MAP_FIXED_SAFE never clobbers a pre-existing +mapped range. If the requested range would collide with an existing +mapping, then this call fails with +.B EEXIST. +This flag can therefore be used as a way to atomically (with respect to other +threads) attempt to map an address range: one thread will succeed; all others +will report failure. Please note that older kernels which do not recognize this +flag will typically (upon detecting a collision with a pre-existing mapping) +fall back a "non-MAP_FIXED" type of behavior: they will return an address that +is different than the requested one. Therefore, backward-compatible software +should check the returned address against the requested address. +.TP .B MAP_GROWSDOWN This flag is used for stacks. It indicates to the kernel virtual memory system that the mapping @@ -449,6 +465,12 @@ is not a valid file descriptor (and .B MAP_ANONYMOUS was not set). .TP +.B EEXIST +range covered by +.IR addr , +.IR length +is clashing with an existing mapping. +.TP .B EINVAL We don't like .IR addr , -- 2.15.0 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: [PATCH v2] mmap.2: document new MAP_FIXED_SAFE flag Date: Thu, 30 Nov 2017 09:24:05 +0100 Message-ID: <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> References: <20171129144219.22867-1-mhocko@kernel.org> <20171129144524.23518-1-mhocko@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20171129144524.23518-1-mhocko@kernel.org> Sender: owner-linux-mm@kvack.org To: Michael Kerrisk Cc: linux-api@vger.kernel.org, Khalid Aziz , Michael Ellerman , Andrew Morton , Russell King - ARM Linux , Andrea Arcangeli , linux-mm@kvack.org, LKML , linux-arch@vger.kernel.org, Florian Weimer , John Hubbard List-Id: linux-arch.vger.kernel.org Updated version based on feedback from John. --- >From ade1eba229b558431581448e7d7838f0e1fe2c49 Mon Sep 17 00:00:00 2001 From: Michal Hocko Date: Wed, 29 Nov 2017 15:32:08 +0100 Subject: [PATCH] mmap.2: document new MAP_FIXED_SAFE flag 4.16+ kernels offer a new MAP_FIXED_SAFE flag which allows the caller to atomicaly probe for a given address range. [wording heavily updated by John Hubbard ] Signed-off-by: Michal Hocko --- man2/mmap.2 | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/man2/mmap.2 b/man2/mmap.2 index 385f3bfd5393..923bbb290875 100644 --- a/man2/mmap.2 +++ b/man2/mmap.2 @@ -225,6 +225,22 @@ will fail. Because requiring a fixed address for a mapping is less portable, the use of this option is discouraged. .TP +.BR MAP_FIXED_SAFE " (since Linux 4.16)" +Similar to MAP_FIXED with respect to the +.I +addr +enforcement, but different in that MAP_FIXED_SAFE never clobbers a pre-existing +mapped range. If the requested range would collide with an existing +mapping, then this call fails with +.B EEXIST. +This flag can therefore be used as a way to atomically (with respect to other +threads) attempt to map an address range: one thread will succeed; all others +will report failure. Please note that older kernels which do not recognize this +flag will typically (upon detecting a collision with a pre-existing mapping) +fall back a "non-MAP_FIXED" type of behavior: they will return an address that +is different than the requested one. Therefore, backward-compatible software +should check the returned address against the requested address. +.TP .B MAP_GROWSDOWN This flag is used for stacks. It indicates to the kernel virtual memory system that the mapping @@ -449,6 +465,12 @@ is not a valid file descriptor (and .B MAP_ANONYMOUS was not set). .TP +.B EEXIST +range covered by +.IR addr , +.IR length +is clashing with an existing mapping. +.TP .B EINVAL We don't like .IR addr , -- 2.15.0 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:41646 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750830AbdK3IYH (ORCPT ); Thu, 30 Nov 2017 03:24:07 -0500 Date: Thu, 30 Nov 2017 09:24:05 +0100 From: Michal Hocko Subject: [PATCH v2] mmap.2: document new MAP_FIXED_SAFE flag Message-ID: <20171130082405.b77eknaiblgmpa4s@dhcp22.suse.cz> References: <20171129144219.22867-1-mhocko@kernel.org> <20171129144524.23518-1-mhocko@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171129144524.23518-1-mhocko@kernel.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Michael Kerrisk Cc: linux-api@vger.kernel.org, Khalid Aziz , Michael Ellerman , Andrew Morton , Russell King - ARM Linux , Andrea Arcangeli , linux-mm@kvack.org, LKML , linux-arch@vger.kernel.org, Florian Weimer , John Hubbard Message-ID: <20171130082405.-4PJlPq3dv0NHq8cVwRY9CPvV_RF50iLk0Mz3ckRKyc@z> Updated version based on feedback from John. ---