From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760831Ab3K0CEK (ORCPT ); Tue, 26 Nov 2013 21:04:10 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:38842 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756950Ab3K0A4v (ORCPT ); Tue, 26 Nov 2013 19:56:51 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Fan Du , Andrew Morton , Linus Torvalds , Zhao Hongjiang Subject: [PATCH 3.4 18/39] include/linux/fs.h: disable preempt when acquire i_size_seqcount write lock Date: Tue, 26 Nov 2013 16:56:42 -0800 Message-Id: <20131127005620.303584957@linuxfoundation.org> X-Mailer: git-send-email 1.8.5.rc3 In-Reply-To: <20131127005619.011763867@linuxfoundation.org> References: <20131127005619.011763867@linuxfoundation.org> User-Agent: quilt/0.60-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Fan Du commit 74e3d1e17b2e11d175970b85acd44f5927000ba2 upstream. Two rt tasks bind to one CPU core. The higher priority rt task A preempts a lower priority rt task B which has already taken the write seq lock, and then the higher priority rt task A try to acquire read seq lock, it's doomed to lockup. rt task A with lower priority: call write i_size_write rt task B with higher priority: call sync, and preempt task A write_seqcount_begin(&inode->i_size_seqcount); i_size_read inode->i_size = i_size; read_seqcount_begin <-- lockup here... So disable preempt when acquiring every i_size_seqcount *write* lock will cure the problem. Signed-off-by: Fan Du Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Cc: Zhao Hongjiang Signed-off-by: Greg Kroah-Hartman --- include/linux/fs.h | 2 ++ 1 file changed, 2 insertions(+) --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -915,9 +915,11 @@ static inline loff_t i_size_read(const s static inline void i_size_write(struct inode *inode, loff_t i_size) { #if BITS_PER_LONG==32 && defined(CONFIG_SMP) + preempt_disable(); write_seqcount_begin(&inode->i_size_seqcount); inode->i_size = i_size; write_seqcount_end(&inode->i_size_seqcount); + preempt_enable(); #elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPT) preempt_disable(); inode->i_size = i_size;