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authorDave Chinner <dchinner@redhat.com>2018-11-19 13:31:10 -0800
committerDarrick J. Wong <darrick.wong@oracle.com>2018-11-21 10:10:53 -0800
commit0929d8580071c6a1cec1a7916a8f674c243ceee1 (patch)
tree665fe3dd2d8f33b072b2a1d62bd73517a7160b4e
parent9230a0b65b47fe6856c4468ec0175c4987e5bede (diff)
downloadlinux-0929d8580071c6a1cec1a7916a8f674c243ceee1.tar.bz2
iomap: FUA is wrong for DIO O_DSYNC writes into unwritten extents
When we write into an unwritten extent via direct IO, we dirty metadata on IO completion to convert the unwritten extent to written. However, when we do the FUA optimisation checks, the inode may be clean and so we issue a FUA write into the unwritten extent. This means we then bypass the generic_write_sync() call after unwritten extent conversion has ben done and we don't force the modified metadata to stable storage. This violates O_DSYNC semantics. The window of exposure is a single IO, as the next DIO write will see the inode has dirty metadata and hence will not use the FUA optimisation. Calling generic_write_sync() after completion of the second IO will also sync the first write and it's metadata. Fix this by avoiding the FUA optimisation when writing to unwritten extents. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
-rw-r--r--fs/iomap.c11
1 files changed, 6 insertions, 5 deletions
diff --git a/fs/iomap.c b/fs/iomap.c
index 64ce240217a1..72f3864a2e6b 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1596,12 +1596,13 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
if (iomap->flags & IOMAP_F_NEW) {
need_zeroout = true;
- } else {
+ } else if (iomap->type == IOMAP_MAPPED) {
/*
- * Use a FUA write if we need datasync semantics, this
- * is a pure data IO that doesn't require any metadata
- * updates and the underlying device supports FUA. This
- * allows us to avoid cache flushes on IO completion.
+ * Use a FUA write if we need datasync semantics, this is a pure
+ * data IO that doesn't require any metadata updates (including
+ * after IO completion such as unwritten extent conversion) and
+ * the underlying device supports FUA. This allows us to avoid
+ * cache flushes on IO completion.
*/
if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) &&
(dio->flags & IOMAP_DIO_WRITE_FUA) &&