On Mon 04-01-21 16:54:40, Eric Biggers wrote:
From: Eric Biggers ebiggers@google.com
When lazytime is enabled and an inode with dirty timestamps is being expired, either due to dirtytime_expire_interval being exceeded or due to a sync or syncfs system call, we need to inform the filesystem that the inode is dirty so that the inode's timestamps can be copied out to the on-disk data structures. That's because if the filesystem supports lazytime, it will have ignored the ->dirty_inode(inode, I_DIRTY_TIME) notification when the timestamp was modified in memory.
Currently this is accomplished by calling mark_inode_dirty_sync() from __writeback_single_inode(). However, this has the unfortunate side effect of also putting the inode the writeback list. That's not appropriate in this case, since the inode is already being written.
That causes the inode to remain dirty after a sync. Normally that's just wasteful, as it causes the inode to be written twice. But when fscrypt is used this bug also partially breaks the FS_IOC_REMOVE_ENCRYPTION_KEY ioctl, as the ioctl reports that files are still in-use when they aren't. For more details, see the original report at https://lore.kernel.org/r/20200306004555.GB225345@gmail.com
Fix this by calling ->dirty_inode(inode, I_DIRTY_SYNC) directly instead of mark_inode_dirty_sync().
This fixes xfstest generic/580 when lazytime is enabled.
A later patch will introduce a ->lazytime_expired method to cleanly separate out the lazytime expiration case, in particular for XFS which uses the VFS-level dirtiness tracking only for lazytime. But that's separate from fixing this bug. Also, note that XFS will incorrectly ignore the I_DIRTY_SYNC notification from __writeback_single_inode() both before and after this patch, as I_DIRTY_TIME was already cleared in i_state. Later patches will fix this separate bug.
Fixes: 0ae45f63d4ef ("vfs: add support for a lazytime mount option") Cc: stable@vger.kernel.org Signed-off-by: Eric Biggers ebiggers@google.com
Good catch! It could also cause issues with filesystem freezing which kind of assumes that the filesystem will be clean after sync_filesystem() (otherwise writeback threads can get stalled on frozen filesystem while holding some locks and generally the system behavior becomes kind of awkward).
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index acfb55834af23..081e335cdee47 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -1509,11 +1509,22 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) spin_unlock(&inode->i_lock);
- if (dirty & I_DIRTY_TIME)
mark_inode_dirty_sync(inode);int err = write_inode(inode, wbc);
int err;/** If the inode is being written due to a lazytime timestamp* expiration, then the filesystem needs to be notified about it* so that e.g. the filesystem can update on-disk fields and* journal the timestamp update. Just calling write_inode()* isn't enough. Don't call mark_inode_dirty_sync(), as that* would put the inode back on the dirty list.*/if ((dirty & I_DIRTY_TIME) && inode->i_sb->s_op->dirty_inode)inode->i_sb->s_op->dirty_inode(inode, I_DIRTY_SYNC);err = write_inode(inode, wbc);
I have to say I dislike this special call of ->dirty_inode(). It works but it makes me wonder, didn't we forget about something or won't we forget in the future? Because it's very easy to miss this special case...
I think attached patch (compile-tested only) should actually fix the problem as well without this special ->dirty_inode() call. It basically only moves the mark_inode_dirty_sync() before inode->i_state clearing. Because conceptually mark_inode_dirty_sync() is IMO the right function to call. It will take care of clearing I_DIRTY_TIME flag (because we are setting I_DIRTY_SYNC), it will also not touch inode->i_io_list if the inode is queued for sync (I_SYNC_QUEUED is set in that case). The only problem with calling it was that it was called *after* clearing dirty bits from i_state... What do you think?
Honza