From: Boaz Harrosh <boaz@plexistor.com>
To: Dave Chinner <david@fromorbit.com>,
Matthew Wilcox <matthew.r.wilcox@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Jan Kara <jack@suse.cz>, Hugh Dickins <hughd@google.com>,
Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org, linux-nvdimm <linux-nvdimm@ml01.01.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Eryu Guan <eguan@redhat.com>
Subject: [PATCH 3/3] RFC: dax: dax_prepare_freeze
Date: Mon, 23 Mar 2015 14:54:40 +0200 [thread overview]
Message-ID: <55100D10.6090902@plexistor.com> (raw)
In-Reply-To: <55100B78.501@plexistor.com>
From: Boaz Harrosh <boaz@plexistor.com>
When freezing an FS, we must write protect all IS_DAX()
inodes that have an mmap mapping on an inode. Otherwise
application will be able to modify previously faulted-in
file pages.
I'm actually doing a full unmap_mapping_range because
there is no readily available "mapping_write_protect" like
functionality. I do not think it is worth it to define one
just for here and just for some extra read-faults after an
fs_freeze.
How hot-path is fs_freeze at all?
CC: Jan Kara <jack@suse.cz>
CC: Matthew Wilcox <matthew.r.wilcox@intel.com>
CC: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Boaz Harrosh <boaz@plexistor.com>
---
fs/dax.c | 30 ++++++++++++++++++++++++++++++
fs/super.c | 3 +++
include/linux/fs.h | 1 +
3 files changed, 34 insertions(+)
diff --git a/fs/dax.c b/fs/dax.c
index d0bd1f4..f3fc28b 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -549,3 +549,33 @@ int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
return dax_zero_page_range(inode, from, length, get_block);
}
EXPORT_SYMBOL_GPL(dax_truncate_page);
+
+/* This is meant to be called as part of freeze_super. otherwise we might
+ * Need some extra locking before calling here.
+ */
+void dax_prepare_freeze(struct super_block *sb)
+{
+ struct inode *inode;
+
+ /* TODO: each DAX fs has some private mount option to enable DAX. If
+ * We made that option a generic MS_DAX_ENABLE super_block flag we could
+ * Avoid the 95% extra unneeded loop-on-all-inodes every freeze.
+ * if (!(sb->s_flags & MS_DAX_ENABLE))
+ * return 0;
+ */
+
+ list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
+ /* TODO: For freezing we can actually do with write-protecting
+ * the page. But I cannot find a ready made function that does
+ * that for a giving mapping (with all the proper locking).
+ * How performance sensitive is the all sb_freeze API?
+ * For now we can just unmap the all mapping, and pay extra
+ * on read faults.
+ */
+ /* NOTE: Do not unmap private COW mapped pages it will not
+ * modify the FS.
+ */
+ if (IS_DAX(inode))
+ unmap_mapping_range(inode->i_mapping, 0, 0, 0);
+ }
+}
diff --git a/fs/super.c b/fs/super.c
index 2b7dc90..9ef490c 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1329,6 +1329,9 @@ int freeze_super(struct super_block *sb)
/* All writers are done so after syncing there won't be dirty data */
sync_filesystem(sb);
+ /* Need to take care of DAX mmaped inodes */
+ dax_prepare_freeze(sb);
+
/* Now wait for internal filesystem counter */
sb->s_writers.frozen = SB_FREEZE_FS;
smp_wmb();
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 24af817..3b943d4 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2599,6 +2599,7 @@ int dax_truncate_page(struct inode *, loff_t from, get_block_t);
int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
int dax_pfn_mkwrite(struct vm_area_struct *, struct vm_fault *);
#define dax_mkwrite(vma, vmf, gb) dax_fault(vma, vmf, gb)
+void dax_prepare_freeze(struct super_block *sb);
#ifdef CONFIG_BLOCK
typedef void (dio_submit_t)(int rw, struct bio *bio, struct inode *inode,
--
1.9.3
--
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next prev parent reply other threads:[~2015-03-23 12:54 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-23 12:47 [PATCH 0/3 v3] dax: Fix mmap-write not updating c/mtime Boaz Harrosh
2015-03-23 12:49 ` [PATCH 1/3] mm: New pfn_mkwrite same as page_mkwrite for VM_PFNMAP Boaz Harrosh
2015-03-23 22:49 ` Andrew Morton
2015-03-23 12:52 ` [PATCH 2/3] dax: use pfn_mkwrite to update c/mtime + freeze protection Boaz Harrosh
2015-03-23 12:54 ` Boaz Harrosh [this message]
2015-03-23 22:40 ` [PATCH 3/3] RFC: dax: dax_prepare_freeze Dave Chinner
2015-03-24 6:14 ` Boaz Harrosh
2015-03-25 2:22 ` Dave Chinner
2015-03-25 8:10 ` Boaz Harrosh
2015-03-25 9:29 ` Dave Chinner
2015-03-25 10:19 ` Boaz Harrosh
2015-03-25 20:00 ` Dave Chinner
2015-03-26 8:02 ` Boaz Harrosh
2015-03-26 20:58 ` Dave Chinner
2015-03-24 12:37 ` Boaz Harrosh
2015-03-25 2:26 ` Dave Chinner
2015-03-25 8:31 ` Boaz Harrosh
2015-03-25 9:41 ` Dave Chinner
2015-03-25 10:40 ` Boaz Harrosh
2015-03-25 20:05 ` Dave Chinner
2015-03-23 12:56 ` [PATCH v4] xfstest: generic/080 test that mmap-write updates c/mtime Boaz Harrosh
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