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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Alistair Popple wrote: > On Wed, Jan 08, 2025 at 04:14:20PM -0800, Dan Williams wrote: > > Alistair Popple wrote: > > > Prior to freeing a block file systems supporting FS DAX must check > > > that the associated pages are both unmapped from user-space and not > > > undergoing DMA or other access from eg. get_user_pages(). This is > > > achieved by unmapping the file range and scanning the FS DAX > > > page-cache to see if any pages within the mapping have an elevated > > > refcount. > > > > > > This is done using two functions - dax_layout_busy_page_range() which > > > returns a page to wait for the refcount to become idle on. Rather than > > > open-code this introduce a common implementation to both unmap and > > > wait for the page to become idle. > > > > > > Signed-off-by: Alistair Popple > > > > > > --- > > > > > > Changes for v5: > > > > > > - Don't wait for idle pages on non-DAX mappings > > > > > > Changes for v4: > > > > > > - Fixed some build breakage due to missing symbol exports reported by > > > John Hubbard (thanks!). > > > --- > > > fs/dax.c | 33 +++++++++++++++++++++++++++++++++ > > > fs/ext4/inode.c | 10 +--------- > > > fs/fuse/dax.c | 29 +++++------------------------ > > > fs/xfs/xfs_inode.c | 23 +++++------------------ > > > fs/xfs/xfs_inode.h | 2 +- > > > include/linux/dax.h | 21 +++++++++++++++++++++ > > > mm/madvise.c | 8 ++++---- > > > 7 files changed, 70 insertions(+), 56 deletions(-) > > > > > > diff --git a/fs/dax.c b/fs/dax.c > > > index d010c10..9c3bd07 100644 > > > --- a/fs/dax.c > > > +++ b/fs/dax.c > > > @@ -845,6 +845,39 @@ int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index) > > > return ret; > > > } > > > > > > +static int wait_page_idle(struct page *page, > > > + void (cb)(struct inode *), > > > + struct inode *inode) > > > +{ > > > + return ___wait_var_event(page, page_ref_count(page) == 1, > > > + TASK_INTERRUPTIBLE, 0, 0, cb(inode)); > > > +} > > > + > > > +/* > > > + * Unmaps the inode and waits for any DMA to complete prior to deleting the > > > + * DAX mapping entries for the range. > > > + */ > > > +int dax_break_mapping(struct inode *inode, loff_t start, loff_t end, > > > + void (cb)(struct inode *)) > > > +{ > > > + struct page *page; > > > + int error; > > > + > > > + if (!dax_mapping(inode->i_mapping)) > > > + return 0; > > > + > > > + do { > > > + page = dax_layout_busy_page_range(inode->i_mapping, start, end); > > > + if (!page) > > > + break; > > > + > > > + error = wait_page_idle(page, cb, inode); > > > > This implementations removes logic around @retry found in the XFS and > > FUSE implementations, I think that is a mistake, and EXT4 has > > apparently been broken in this regard. > > I think both implementations are equivalent though, just that the XFS/FUSE ones are > spread across two functions with the retry happening in the outer function > whilst the EXT4 implementation is implemented in a single function with a do/ > while loop. > > Both exit early if dax_layout_busy_page() doesn't find a DMA-busy page, and > both call dax_layout_busy_page() a second time after waiting on a page to become > idle. So I don't think anything is broken here, unless I've missed something. Nope, you're right. I crossed my eyes flipping between FUSE/XFS and EXT4. > > > wait_page_idle() returns after @page is idle, but that does not mean > > @inode is DMA idle. After one found page from > > dax_layout_busy_page_range() is waited upon a new call to > > dax_break_mapping() needs to made to check if another DMA started, or if > > there were originally more pages active. > > > > > + } while (error == 0); > > > + > > > + return error; > > > > Surprised that the compiler does not warn about an uninitialized > > variable here? > > So am I. Turns out this is built with -Wno-maybe-uninitialized and it's not > certain error is used uninitialized because we may bail early if this is not a > dax_mapping. So it's only maybe used uninitialized which isn't warned about. Looks like smatch just caught it.