From 24f3478d664b1eaa6f8860d3aa521aebe51b2a62 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Thu, 21 Dec 2017 17:04:07 -0800 Subject: ext4: auto disable dax instead of failing mount Bring the ext4 filesystem in line with xfs that only warns and continues when the "-o dax" option is specified to mount and the backing device does not support dax. This is in preparation for removing dax support from devices that do not enable get_user_pages() operations on dax mappings. In other words 'gup' support is required and configurations that were using so called 'page-less' dax will be converted back to using the page cache. Removing the broken 'page-less' dax support is a pre-requisite for removing the "EXPERIMENTAL" warning when mounting a filesystem in dax mode. Reviewed-by: Jan Kara Signed-off-by: Dan Williams --- fs/ext4/super.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) (limited to 'fs') diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 7c46693a14d7..18873ea89e08 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -3710,11 +3710,14 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent) if (ext4_has_feature_inline_data(sb)) { ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem" " that may contain inline data"); - goto failed_mount; + sbi->s_mount_opt &= ~EXT4_MOUNT_DAX; } err = bdev_dax_supported(sb, blocksize); - if (err) - goto failed_mount; + if (err) { + ext4_msg(sb, KERN_ERR, + "DAX unsupported by block device. Turning off DAX."); + sbi->s_mount_opt &= ~EXT4_MOUNT_DAX; + } } if (ext4_has_feature_encrypt(sb) && es->s_encryption_level) { -- cgit From b4b5798cea8f40ab61f3a2c79a26314465dd83e3 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Thu, 21 Dec 2017 18:18:27 -0800 Subject: ext2: auto disable dax instead of failing mount Bring the ext2 filesystem in line with xfs that only warns and continues when the "-o dax" option is specified to mount and the backing device does not support dax. This is in preparation for removing dax support from devices that do not enable get_user_pages() operations on dax mappings. In other words 'gup' support is required and configurations that were using so called 'page-less' dax will be converted back to using the page cache. Removing the broken 'page-less' dax support is a pre-requisite for removing the "EXPERIMENTAL" warning when mounting a filesystem in dax mode. Reviewed-by: Jan Kara Signed-off-by: Dan Williams --- fs/ext2/super.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'fs') diff --git a/fs/ext2/super.c b/fs/ext2/super.c index 7646818ab266..38f9222606ee 100644 --- a/fs/ext2/super.c +++ b/fs/ext2/super.c @@ -959,8 +959,11 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent) if (sbi->s_mount_opt & EXT2_MOUNT_DAX) { err = bdev_dax_supported(sb, blocksize); - if (err) - goto failed_mount; + if (err) { + ext2_msg(sb, KERN_ERR, + "DAX unsupported by block device. Turning off DAX."); + sbi->s_mount_opt &= ~EXT2_MOUNT_DAX; + } } /* If the blocksize doesn't match, re-read the thing.. */ -- cgit From 569d0365f571fa6421a5c80bc30d1b2cdab857fe Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Sat, 14 Oct 2017 11:33:32 -0700 Subject: dax: require 'struct page' by default for filesystem dax If a dax buffer from a device that does not map pages is passed to read(2) or write(2) as a target for direct-I/O it triggers SIGBUS. If gdb attempts to examine the contents of a dax buffer from a device that does not map pages it triggers SIGBUS. If fork(2) is called on a process with a dax mapping from a device that does not map pages it triggers SIGBUS. 'struct page' is required otherwise several kernel code paths break in surprising ways. Disable filesystem-dax on devices that do not map pages. In addition to needing pfn_to_page() to be valid we also require devmap pages. We need this to detect dax pages in the get_user_pages_fast() path and so that we can stop managing the VM_MIXEDMAP flag. For DAX drivers that have not supported get_user_pages() to date we allow them to opt-in to supporting DAX with the CONFIG_FS_DAX_LIMITED configuration option which requires ->direct_access() to return pfn_t_special() pfns. This leaves DAX support in brd disabled and scheduled for removal. Note that when the initial dax support was being merged a few years back there was concern that struct page was unsuitable for use with next generation persistent memory devices. The theoretical concern was that struct page access, being such a hotly used data structure in the kernel, would lead to media wear out. While that was a reasonable conservative starting position it has not held true in practice. We have long since committed to using devm_memremap_pages() to support higher order kernel functionality that needs get_user_pages() and pfn_to_page(). Cc: Jeff Moyer Cc: Ross Zwisler Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Michael Ellerman Cc: Martin Schwidefsky Cc: Heiko Carstens Reviewed-by: Jan Kara Reviewed-by: Christoph Hellwig Reviewed-by: Gerald Schaefer Signed-off-by: Dan Williams --- fs/Kconfig | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'fs') diff --git a/fs/Kconfig b/fs/Kconfig index 7aee6d699fd6..b40128bf6d1a 100644 --- a/fs/Kconfig +++ b/fs/Kconfig @@ -58,6 +58,13 @@ config FS_DAX_PMD depends on ZONE_DEVICE depends on TRANSPARENT_HUGEPAGE +# Selected by DAX drivers that do not expect filesystem DAX to support +# get_user_pages() of DAX mappings. I.e. "limited" indicates no support +# for fork() of processes with MAP_SHARED mappings or support for +# direct-I/O to a DAX mapping. +config FS_DAX_LIMITED + bool + endif # BLOCK # Posix ACL utility routines -- cgit