From patchwork Thu Dec 5 06:46:23 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ritesh Harjani X-Patchwork-Id: 11274263 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id EEE45138D for ; Thu, 5 Dec 2019 06:46:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B98A022525 for ; Thu, 5 Dec 2019 06:46:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726201AbfLEGqm (ORCPT ); Thu, 5 Dec 2019 01:46:42 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:23890 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725974AbfLEGql (ORCPT ); Thu, 5 Dec 2019 01:46:41 -0500 Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id xB56gM5F081040 for ; Thu, 5 Dec 2019 01:46:39 -0500 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0b-001b2d01.pphosted.com with ESMTP id 2wpuwn1m71-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 05 Dec 2019 01:46:39 -0500 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 5 Dec 2019 06:46:33 -0000 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps3075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id xB56kWYx57213062 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 5 Dec 2019 06:46:33 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DD470A4059; Thu, 5 Dec 2019 06:46:32 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 02421A4040; Thu, 5 Dec 2019 06:46:31 +0000 (GMT) Received: from dhcp-9-199-159-163.in.ibm.com (unknown [9.199.159.163]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 5 Dec 2019 06:46:30 +0000 (GMT) From: Ritesh Harjani To: jack@suse.cz, tytso@mit.edu, linux-ext4@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, mbobrowski@mbobrowski.org, riteshh@linux.ibm.com, joseph.qi@linux.alibaba.com Subject: [PATCHv4 2/3] ext4: Start with shared i_rwsem in case of DIO instead of exclusive Date: Thu, 5 Dec 2019 12:16:23 +0530 X-Mailer: git-send-email 2.21.0 In-Reply-To: <20191205064624.13419-1-riteshh@linux.ibm.com> References: <20191205064624.13419-1-riteshh@linux.ibm.com> MIME-Version: 1.0 X-TM-AS-GCONF: 00 x-cbid: 19120506-0028-0000-0000-000003C52B08 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19120506-0029-0000-0000-000024884BEA Message-Id: <20191205064624.13419-3-riteshh@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-12-05_01:2019-12-04,2019-12-05 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 mlxscore=0 bulkscore=0 malwarescore=0 spamscore=0 mlxlogscore=495 clxscore=1015 impostorscore=0 suspectscore=3 lowpriorityscore=0 adultscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1912050052 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Earlier there was no shared lock in DIO read path. But this patch (16c54688592ce: ext4: Allow parallel DIO reads) simplified some of the locking mechanism while still allowing for parallel DIO reads by adding shared lock in inode DIO read path. But this created problem with mixed read/write workload. It is due to the fact that in DIO path, we first start with exclusive lock and only when we determine that it is a ovewrite IO, we downgrade the lock. This causes the problem, since we still have shared locking in DIO reads. So, this patch tries to fix this issue by starting with shared lock and then switching to exclusive lock only when required based on ext4_dio_write_checks(). Other than that, it also simplifies below cases:- 1. Simplified ext4_unaligned_aio API to ext4_unaligned_io. Previous API was abused in the sense that it was not really checking for AIO anywhere also it used to check for extending writes. So this API was renamed and simplified to ext4_unaligned_io() which actully only checks if the IO is really unaligned. Now, in case of unaligned direct IO, iomap_dio_rw needs to do zeroing of partial block and that will require serialization against other direct IOs in the same block. So we take a exclusive inode lock for any unaligned DIO. In case of AIO we also need to wait for any outstanding IOs to complete so that conversion from unwritten to written is completed before anyone try to map the overlapping block. Hence we take exclusive inode lock and also wait for inode_dio_wait() for unaligned DIO case. Please note since we are anyway taking an exclusive lock in unaligned IO, inode_dio_wait() becomes a no-op in case of non-AIO DIO. 2. Added ext4_extending_io(). This checks if the IO is extending the file. 3. Added ext4_dio_write_checks(). In this we start with shared inode lock and only switch to exclusive lock if required. So in most cases with aligned, non-extending, dioread_nolock & overwrites, it tries to write with a shared lock. If not, then we restart the operation in ext4_dio_write_checks(), after acquiring exclusive lock. Signed-off-by: Ritesh Harjani Reviewed-by: Jan Kara --- fs/ext4/file.c | 189 ++++++++++++++++++++++++++++++++++++------------- 1 file changed, 141 insertions(+), 48 deletions(-) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index 977ac58dc718..cbafaec9e4fc 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -166,19 +166,25 @@ static int ext4_release_file(struct inode *inode, struct file *filp) * threads are at work on the same unwritten block, they must be synchronized * or one thread will zero the other's data, causing corruption. */ -static int -ext4_unaligned_aio(struct inode *inode, struct iov_iter *from, loff_t pos) +static bool +ext4_unaligned_io(struct inode *inode, struct iov_iter *from, loff_t pos) { struct super_block *sb = inode->i_sb; - int blockmask = sb->s_blocksize - 1; - - if (pos >= ALIGN(i_size_read(inode), sb->s_blocksize)) - return 0; + unsigned long blockmask = sb->s_blocksize - 1; if ((pos | iov_iter_alignment(from)) & blockmask) - return 1; + return true; - return 0; + return false; +} + +static bool +ext4_extending_io(struct inode *inode, loff_t offset, size_t len) +{ + if (offset + len > i_size_read(inode) || + offset + len > EXT4_I(inode)->i_disksize) + return true; + return false; } /* Is IO overwriting allocated and initialized blocks? */ @@ -204,7 +210,8 @@ static bool ext4_overwrite_io(struct inode *inode, loff_t pos, loff_t len) return err == blklen && (map.m_flags & EXT4_MAP_MAPPED); } -static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from) +static ssize_t ext4_generic_write_checks(struct kiocb *iocb, + struct iov_iter *from) { struct inode *inode = file_inode(iocb->ki_filp); ssize_t ret; @@ -228,11 +235,21 @@ static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from) iov_iter_truncate(from, sbi->s_bitmap_maxbytes - iocb->ki_pos); } + return iov_iter_count(from); +} + +static ssize_t ext4_write_checks(struct kiocb *iocb, struct iov_iter *from) +{ + ssize_t ret, count; + + count = ext4_generic_write_checks(iocb, from); + if (count <= 0) + return count; + ret = file_modified(iocb->ki_filp); if (ret) return ret; - - return iov_iter_count(from); + return count; } static ssize_t ext4_buffered_write_iter(struct kiocb *iocb, @@ -364,62 +381,139 @@ static const struct iomap_dio_ops ext4_dio_write_ops = { .end_io = ext4_dio_write_end_io, }; +/* + * The intention here is to start with shared lock acquired then see if any + * condition requires an exclusive inode lock. If yes, then we restart the + * whole operation by releasing the shared lock and acquiring exclusive lock. + * + * - For unaligned_io we never take shared lock as it may cause data corruption + * when two unaligned IO tries to modify the same block e.g. while zeroing. + * + * - For extending writes case we don't take the shared lock, since it requires + * updating inode i_disksize and/or orphan handling with exclusive lock. + * + * - shared locking will only be true mostly with overwrites in dioread_nolock + * mode. Otherwise we will switch to exclusive i_rwsem lock. + */ +static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from, + bool *ilock_shared, bool *extend) +{ + struct file *file = iocb->ki_filp; + struct inode *inode = file_inode(file); + loff_t offset; + size_t count; + ssize_t ret; + +restart: + ret = ext4_generic_write_checks(iocb, from); + if (ret <= 0) + goto out; + + offset = iocb->ki_pos; + count = iov_iter_count(from); + if (ext4_extending_io(inode, offset, count)) + *extend = true; + /* + * Determine whether the IO operation will overwrite allocated + * and initialized blocks. If so, check to see whether it is + * possible to take the dioread_nolock path. + * + * We need exclusive i_rwsem for changing security info + * in file_modified(). + */ + if (*ilock_shared && (!IS_NOSEC(inode) || *extend || + !ext4_should_dioread_nolock(inode) || + !ext4_overwrite_io(inode, offset, count))) { + inode_unlock_shared(inode); + *ilock_shared = false; + inode_lock(inode); + goto restart; + } + + ret = file_modified(file); + if (ret < 0) + goto out; + + return count; +out: + if (*ilock_shared) + inode_unlock_shared(inode); + else + inode_unlock(inode); + return ret; +} + static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from) { ssize_t ret; - size_t count; - loff_t offset; handle_t *handle; struct inode *inode = file_inode(iocb->ki_filp); - bool extend = false, overwrite = false, unaligned_aio = false; + loff_t offset = iocb->ki_pos; + size_t count = iov_iter_count(from); + bool extend = false, unaligned_io = false; + bool ilock_shared = true; + + /* + * We initially start with shared inode lock unless it is + * unaligned IO which needs exclusive lock anyways. + */ + if (ext4_unaligned_io(inode, from, offset)) { + unaligned_io = true; + ilock_shared = false; + } + /* + * Quick check here without any i_rwsem lock to see if it is extending + * IO. A more reliable check is done in ext4_dio_write_checks() with + * proper locking in place. + */ + if (offset + count > i_size_read(inode)) + ilock_shared = false; if (iocb->ki_flags & IOCB_NOWAIT) { - if (!inode_trylock(inode)) - return -EAGAIN; + if (ilock_shared) { + if (!inode_trylock_shared(inode)) + return -EAGAIN; + } else { + if (!inode_trylock(inode)) + return -EAGAIN; + } } else { - inode_lock(inode); + if (ilock_shared) + inode_lock_shared(inode); + else + inode_lock(inode); } + /* Fallback to buffered I/O if the inode does not support direct I/O. */ if (!ext4_dio_supported(inode)) { - inode_unlock(inode); - /* - * Fallback to buffered I/O if the inode does not support - * direct I/O. - */ + if (ilock_shared) + inode_unlock_shared(inode); + else + inode_unlock(inode); return ext4_buffered_write_iter(iocb, from); } - ret = ext4_write_checks(iocb, from); - if (ret <= 0) { - inode_unlock(inode); + ret = ext4_dio_write_checks(iocb, from, &ilock_shared, &extend); + if (ret <= 0) return ret; - } - /* - * Unaligned asynchronous direct I/O must be serialized among each - * other as the zeroing of partial blocks of two competing unaligned - * asynchronous direct I/O writes can result in data corruption. - */ offset = iocb->ki_pos; count = iov_iter_count(from); - if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) && - !is_sync_kiocb(iocb) && ext4_unaligned_aio(inode, from, offset)) { - unaligned_aio = true; - inode_dio_wait(inode); - } /* - * Determine whether the I/O will overwrite allocated and initialized - * blocks. If so, check to see whether it is possible to take the - * dioread_nolock path. + * Unaligned direct IO must be serialized among each other as zeroing + * of partial blocks of two competing unaligned IOs can result in data + * corruption. + * + * So we make sure we don't allow any unaligned IO in flight. + * For IOs where we need not wait (like unaligned non-AIO DIO), + * below inode_dio_wait() may anyway become a no-op, since we start + * with exclusive lock. */ - if (!unaligned_aio && ext4_overwrite_io(inode, offset, count) && - ext4_should_dioread_nolock(inode)) { - overwrite = true; - downgrade_write(&inode->i_rwsem); - } + if (unaligned_io) + inode_dio_wait(inode); - if (offset + count > EXT4_I(inode)->i_disksize) { + if (extend) { handle = ext4_journal_start(inode, EXT4_HT_INODE, 2); if (IS_ERR(handle)) { ret = PTR_ERR(handle); @@ -432,18 +526,17 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from) goto out; } - extend = true; ext4_journal_stop(handle); } ret = iomap_dio_rw(iocb, from, &ext4_iomap_ops, &ext4_dio_write_ops, - is_sync_kiocb(iocb) || unaligned_aio || extend); + is_sync_kiocb(iocb) || unaligned_io || extend); if (extend) ret = ext4_handle_inode_extension(inode, offset, ret, count); out: - if (overwrite) + if (ilock_shared) inode_unlock_shared(inode); else inode_unlock(inode);