On Wed, Sep 18, 2024 at 07:15:23AM +0200, Christoph Hellwig wrote: > On Tue, Sep 17, 2024 at 02:29:35PM -0700, Darrick J. Wong wrote: > > On Tue, Sep 10, 2024 at 07:39:10AM +0300, Christoph Hellwig wrote: > > > All callers of iomap_zero_range already hold invalidate_lock, so we can't > > > take it again in iomap_file_buffered_write_punch_delalloc. > > > > > > Use the passed in flags argument to detect if we're called from a zeroing > > > operation and don't take the lock again in this case. > > > > > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > > > --- > > > fs/iomap/buffered-io.c | 10 ++++++++-- > > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > > > diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c > > > index 52f285ae4bddcb..3d7e69a542518a 100644 > > > --- a/fs/iomap/buffered-io.c > > > +++ b/fs/iomap/buffered-io.c > > > @@ -1188,8 +1188,13 @@ static void iomap_write_delalloc_release(struct inode *inode, loff_t start_byte, > > > * folios and dirtying them via ->page_mkwrite whilst we walk the > > > * cache and perform delalloc extent removal. Failing to do this can > > > * leave dirty pages with no space reservation in the cache. > > > + * > > > + * For zeroing operations the callers already hold invalidate_lock. > > > */ > > > - filemap_invalidate_lock(inode->i_mapping); > > > + if (flags & IOMAP_ZERO) > > > + rwsem_assert_held_write(&inode->i_mapping->invalidate_lock); > > > > Does the other iomap_zero_range user (gfs2) take the invalidate lock? > > AFAICT it doesn't. Shouldn't we annotate iomap_zero_range to say that > > callers have to hold i_rwsem and the invalidate_lock? > > gfs2 does not hold invalidate_lock over iomap_zero_range. But > it also does not use iomap_file_buffered_write_punch_delalloc at > all, which is what requires the lock (and asserts that it is held). Not a fan of this dichotomy. It means that filesystems that don't support IOMAP_DELALLOC don't need to hold the invalidate lock to zero, but filesystems that do support IOMAP_DELALLOC do need to hold it. I'd kinda prefer there be one locking rule for all callers; it makes it much easy to determine if the callers are doing the right thing without needing to know if the filesystem is IOMAP_DELALLOC capable or not. At minimum, it needs to be clearly documented. -Dave. -- Dave Chinner david@xxxxxxxxxxxxx
