From: Dave Chinner dchinner@redhat.com
[ Upstream commit 0929d8580071c6a1cec1a7916a8f674c243ceee1 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- fs/iomap.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/fs/iomap.c b/fs/iomap.c index fac45206418a2..914c07c9e0d6f 100644 --- a/fs/iomap.c +++ b/fs/iomap.c @@ -1619,12 +1619,13 @@ 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) &&