[PATCH v7 03/12] fs: introduce i_mapdcount
From: Dan Williams <hidden>
Date: 2017-10-06 22:35:32
Also in:
linux-fsdevel, linux-mm, linux-rdma, linux-xfs, nvdimm
Subsystem:
filesystems (vfs and infrastructure), the rest, xfs filesystem · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds, Carlos Maiolino
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@suse.cz> Cc: Jeff Moyer <redacted> Cc: Christoph Hellwig <hch@lst.de> Cc: Dave Chinner <david@fromorbit.com> Cc: "Darrick J. Wong" <redacted> Cc: Ross Zwisler <redacted> Cc: Jeff Layton <redacted> Cc: "J. Bruce Fields" <redacted> Signed-off-by: Dan Williams <redacted> --- 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) \ --
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