{"id":814406,"url":"http://patchwork.ozlabs.org/api/1.2/patches/814406/?format=json","web_url":"http://patchwork.ozlabs.org/project/ubuntu-kernel/patch/1505511880-19182-2-git-send-email-marcelo.cerri@canonical.com/","project":{"id":15,"url":"http://patchwork.ozlabs.org/api/1.2/projects/15/?format=json","name":"Ubuntu Kernel","link_name":"ubuntu-kernel","list_id":"kernel-team.lists.ubuntu.com","list_email":"kernel-team@lists.ubuntu.com","web_url":null,"scm_url":null,"webscm_url":null,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<1505511880-19182-2-git-send-email-marcelo.cerri@canonical.com>","list_archive_url":null,"date":"2017-09-15T21:44:38","name":"[azure,1/3] ext4: fix fault handling when mounted with -o dax, ro","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"17c01719e82ce8faf8a96561aaa02784625685bb","submitter":{"id":69981,"url":"http://patchwork.ozlabs.org/api/1.2/people/69981/?format=json","name":"Marcelo Henrique Cerri","email":"marcelo.cerri@canonical.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/ubuntu-kernel/patch/1505511880-19182-2-git-send-email-marcelo.cerri@canonical.com/mbox/","series":[{"id":3388,"url":"http://patchwork.ozlabs.org/api/1.2/series/3388/?format=json","web_url":"http://patchwork.ozlabs.org/project/ubuntu-kernel/list/?series=3388","date":"2017-09-15T21:44:37","name":"linux-azure: persistent memory is not working","version":1,"mbox":"http://patchwork.ozlabs.org/series/3388/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/814406/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/814406/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@bilbo.ozlabs.org","Authentication-Results":"ozlabs.org;\n\tspf=none (mailfrom) smtp.mailfrom=lists.ubuntu.com\n\t(client-ip=91.189.94.19; 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charset=\"utf-8\"","Content-Transfer-Encoding":"base64","Errors-To":"kernel-team-bounces@lists.ubuntu.com","Sender":"\"kernel-team\" "},"content":"From: Randy Dodgen \n\nBugLink: http://bugs.launchpad.net/bugs/1715755\n\nIf an ext4 filesystem is mounted with both the DAX and read-only\noptions, executables on that filesystem will fail to start (claiming\n'Segmentation fault') due to the fault handler returning\nVM_FAULT_SIGBUS.\n\nThis is due to the DAX fault handler (see ext4_dax_huge_fault)\nattempting to write to the journal when FAULT_FLAG_WRITE is set. This is\nthe wrong behavior for write faults which will lead to a COW page; in\nparticular, this fails for readonly mounts.\n\nThis change avoids journal writes for faults that are expected to COW.\n\nIt might be the case that this could be better handled in\next4_iomap_begin / ext4_iomap_end (called via iomap_ops inside\ndax_iomap_fault). These is some overlap already (e.g. grabbing journal\nhandles).\n\nSigned-off-by: Randy Dodgen \nSigned-off-by: Theodore Ts'o \nReviewed-by: Jan Kara \nReviewed-by: Ross Zwisler \n(cherry picked from commit fd96b8da68d32a9403726db09b229f4b5ac849c7)\nSigned-off-by: Marcelo Henrique Cerri \n---\n fs/ext4/file.c | 15 ++++++++++++++-\n 1 file changed, 14 insertions(+), 1 deletion(-)","diff":"diff --git a/fs/ext4/file.c b/fs/ext4/file.c\nindex bbea2dccd584..2ac020b3cbf8 100644\n--- a/fs/ext4/file.c\n+++ b/fs/ext4/file.c\n@@ -260,7 +260,20 @@ static int ext4_dax_huge_fault(struct vm_fault *vmf,\n \thandle_t *handle = NULL;\n \tstruct inode *inode = file_inode(vmf->vma->vm_file);\n \tstruct super_block *sb = inode->i_sb;\n-\tbool write = vmf->flags & FAULT_FLAG_WRITE;\n+\n+\t/*\n+\t * We have to distinguish real writes from writes which will result in a\n+\t * COW page; COW writes should *not* poke the journal (the file will not\n+\t * be changed). Doing so would cause unintended failures when mounted\n+\t * read-only.\n+\t *\n+\t * We check for VM_SHARED rather than vmf->cow_page since the latter is\n+\t * unset for pe_size != PE_SIZE_PTE (i.e. only in do_cow_fault); for\n+\t * other sizes, dax_iomap_fault will handle splitting / fallback so that\n+\t * we eventually come back with a COW page.\n+\t */\n+\tbool write = (vmf->flags & FAULT_FLAG_WRITE) &&\n+\t\t(vmf->vma->vm_flags & VM_SHARED);\n \n \tif (write) {\n \t\tsb_start_pagefault(sb);\n","prefixes":["azure","1/3"]}