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Wong" Date: Tue, 3 Aug 2021 21:18:13 +0200 Message-Id: <20210803191818.993968-8-agruenba@redhat.com> In-Reply-To: <20210803191818.993968-1-agruenba@redhat.com> References: <20210803191818.993968-1-agruenba@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Proofpoint-SPF-Result: pass X-Proofpoint-SPF-Record: v=spf1 ip4:103.23.64.2 ip4:103.23.65.2 ip4:103.23.66.26 ip4:103.23.67.26 ip4:107.21.15.141 ip4:108.177.8.0/21 ip4:128.17.0.0/20 ip4:128.17.128.0/20 ip4:128.17.192.0/20 ip4:128.17.64.0/20 ip4:128.245.0.0/20 ip4:128.245.64.0/20 ip4:13.110.208.0/21 ip4:13.111.0.0/16 ip4:136.147.128.0/20 ip4:136.147.176.0/20 ip4:148.105.8.0/21 ip4:148.139.0.2 include:spf1.redhat.com -all X-Proofpoint-SPF-VenPass: Allowed X-Source-IP: 170.10.133.124 X-ServerName: us-smtp-delivery-124.mimecast.com X-Proofpoint-SPF-Result: pass X-Proofpoint-SPF-Record: v=spf1 ip4:103.23.64.2 ip4:103.23.65.2 ip4:103.23.66.26 ip4:103.23.67.26 ip4:107.21.15.141 ip4:108.177.8.0/21 ip4:128.17.0.0/20 ip4:128.17.128.0/20 ip4:128.17.192.0/20 ip4:128.17.64.0/20 ip4:128.245.0.0/20 ip4:128.245.64.0/20 ip4:13.110.208.0/21 ip4:13.111.0.0/16 ip4:136.147.128.0/20 ip4:136.147.176.0/20 ip4:148.105.8.0/21 ip4:148.139.0.2 include:spf1.redhat.com -all X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10065 signatures=668682 X-Proofpoint-Spam-Reason: safe X-Spam: OrgSafeList X-SpamRule: orgsafelist X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10065 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 mlxscore=0 adultscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108030123 Cc: Jan Kara , Andreas Gruenbacher , linux-kernel@vger.kernel.org, cluster-devel@redhat.com, linux-fsdevel@vger.kernel.org, ocfs2-devel@oss.oracle.com Subject: [Ocfs2-devel] [PATCH v5 07/12] gfs2: Fix mmap + page fault deadlocks for buffered I/O X-BeenThere: ocfs2-devel@oss.oracle.com X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: ocfs2-devel-bounces@oss.oracle.com Errors-To: ocfs2-devel-bounces@oss.oracle.com X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10065 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 phishscore=0 malwarescore=0 suspectscore=0 mlxscore=0 adultscore=0 mlxlogscore=999 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2107140000 definitions=main-2108030123 X-Proofpoint-GUID: t1q2D0O6jyUOrG4-pUVn7FpyQ01YV3U4 X-Proofpoint-ORIG-GUID: t1q2D0O6jyUOrG4-pUVn7FpyQ01YV3U4 In the .read_iter and .write_iter file operations, we're accessing user-space memory while holding the inodes glock. There's a possibility that the memory is mapped to the same file, in which case we'd recurse on the same glock. More complex scenarios can involve multiple glocks, processes, and even cluster nodes. Avoids these kinds of problems by disabling page faults while holding a glock. If a page fault occurs, we either end up with a partial read or write, or with -EFAULT if nothing could be read or written. In that case, we drop the glock, fault in the requested pages manually, and repeat the operation. This locking problem in gfs2 was originally reported by Jan Kara. Linus came up with the proposal to disable page faults. Many thanks to Al Viro and Matthew Wilcox for their feedback as well. Signed-off-by: Andreas Gruenbacher --- fs/gfs2/file.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c index 55ec1cadc9e6..c0f86a28f1bf 100644 --- a/fs/gfs2/file.c +++ b/fs/gfs2/file.c @@ -843,6 +843,12 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to) size_t written = 0; ssize_t ret; + /* + * In this function, we disable page faults when we're holding the + * inode glock while doing I/O. If a page fault occurs, we drop the + * inode glock, fault in the pages manually, and retry. + */ + if (iocb->ki_flags & IOCB_DIRECT) { ret = gfs2_file_direct_read(iocb, to, &gh); if (likely(ret != -ENOTBLK)) @@ -864,13 +870,20 @@ static ssize_t gfs2_file_read_iter(struct kiocb *iocb, struct iov_iter *to) } ip = GFS2_I(iocb->ki_filp->f_mapping->host); gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh); +retry: ret = gfs2_glock_nq(&gh); if (ret) goto out_uninit; + pagefault_disable(); ret = generic_file_read_iter(iocb, to); + pagefault_enable(); if (ret > 0) written += ret; gfs2_glock_dq(&gh); + if (unlikely(iov_iter_count(to) && (ret > 0 || ret == -EFAULT)) && + iter_is_iovec(to) && + fault_in_iov_iter_writeable(to, SIZE_MAX) != 0) + goto retry; out_uninit: gfs2_holder_uninit(&gh); return written ? written : ret; @@ -882,9 +895,22 @@ static ssize_t gfs2_file_buffered_write(struct kiocb *iocb, struct iov_iter *fro struct inode *inode = file_inode(file); ssize_t ret; + /* + * In this function, we disable page faults when we're holding the + * inode glock while doing I/O. If a page fault occurs, we drop the + * inode glock, fault in the pages manually, and retry. + */ + +retry: current->backing_dev_info = inode_to_bdi(inode); + pagefault_disable(); ret = iomap_file_buffered_write(iocb, from, &gfs2_iomap_ops); + pagefault_enable(); current->backing_dev_info = NULL; + if (unlikely(ret == -EFAULT) && + iter_is_iovec(from) && + fault_in_iov_iter_readable(from, SIZE_MAX) != 0) + goto retry; return ret; } -- 2.26.3 _______________________________________________ Ocfs2-devel mailing list Ocfs2-devel@oss.oracle.com https://oss.oracle.com/mailman/listinfo/ocfs2-devel