When ->iomap_begin() sees this count being non-zero and determines that
the block map of the file needs to be modified to satisfy the I/O
request it will instead return an error. This is needed for MAP_DIRECT
where, due to locking constraints, we can't rely on xfs_break_layouts()
to protect against allocating write-faults either from the process that
setup the MAP_DIRECT mapping nor other processes that have the file
mapped. xfs_break_layouts() requires XFS_IOLOCK which is problematic to
mix with the XFS_MMAPLOCK in the fault path.
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: "Darrick J. Wong" <darrick.wong@xxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxxxxxxx>
Cc: "J. Bruce Fields" <bfields@xxxxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
fs/xfs/xfs_iomap.c | 9 +++++++++
include/linux/fs.h | 31 +++++++++++++++++++++++++++++++
2 files changed, 40 insertions(+)
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index a1909bc064e9..6816f8ebbdcf 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1053,6 +1053,15 @@ xfs_file_iomap_begin(
goto out_unlock;
}
/*
+ * If a file has MAP_DIRECT mappings disable block map
+ * updates. This should only effect mmap write faults as
+ * other paths are protected by an FL_LAYOUT lease.
+ */
+ if (i_mapdcount_read(inode)) {
+ error = -ETXTBSY;
+ goto out_unlock;
+ }
+ /*
* We cap the maximum length we map here to MAX_WRITEBACK_PAGES
* pages to keep the chunks of work done where somewhat symmetric
* with the work writeback does. This is a completely arbitrary
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c2b9bf3dc4e9..f83871b188ff 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -642,6 +642,9 @@ struct inode {
atomic_t i_count;
atomic_t i_dio_count;
atomic_t i_writecount;
+#ifdef CONFIG_FS_DAX
+ atomic_t i_mapdcount; /* count of MAP_DIRECT vmas */
+#endif
#ifdef CONFIG_IMA
atomic_t i_readcount; /* struct files open RO */
#endif
@@ -2784,6 +2787,34 @@ static inline void i_readcount_inc(struct inode *inode)
return;
}
#endif
+
+#ifdef CONFIG_FS_DAX
+static inline void i_mapdcount_dec(struct inode *inode)
+{
+ BUG_ON(!atomic_read(&inode->i_mapdcount));
+ atomic_dec(&inode->i_mapdcount);
+}
+static inline void i_mapdcount_inc(struct inode *inode)
+{
+ atomic_inc(&inode->i_mapdcount);
+}
+static inline int i_mapdcount_read(struct inode *inode)
+{
+ return atomic_read(&inode->i_mapdcount);
+}
+#else
+static inline void i_mapdcount_dec(struct inode *inode)
+{
+}
+static inline void i_mapdcount_inc(struct inode *inode)
+{
+}
+static inline int i_mapdcount_read(struct inode *inode)
+{
+ return 0;
+}
+#endif
+
extern int do_pipe_flags(int *, int);
#define __kernel_read_file_id(id) \
