On Mon, Aug 08, 2022 at 09:08:10AM +1000, Dave Chinner wrote: > On Wed, Aug 03, 2022 at 12:53:39PM +0200, Lukas Czerner wrote: > > Currently the I_DIRTY_TIME will never get set if the inode already has > > I_DIRTY_INODE with assumption that it supersedes I_DIRTY_TIME. That's > > true, however ext4 will only update the on-disk inode in > > ->dirty_inode(), not on actual writeback. As a result if the inode > > already has I_DIRTY_INODE state by the time we get to > > __mark_inode_dirty() only with I_DIRTY_TIME, the time was already filled > > into on-disk inode and will not get updated until the next I_DIRTY_INODE > > update, which might never come if we crash or get a power failure. > > > > The problem can be reproduced on ext4 by running xfstest generic/622 > > with -o iversion mount option. > > > > Fix it by allowing I_DIRTY_TIME to be set even if the inode already has > > I_DIRTY_INODE. Also make sure that the case is properly handled in > > writeback_single_inode() as well. Additionally changes in > > xfs_fs_dirty_inode() was made to accommodate for I_DIRTY_TIME in flag. > > > > Thanks Jan Kara for suggestions on how to make this work properly. > > > > Cc: Dave Chinner <david@xxxxxxxxxxxxx> > > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx> > > Signed-off-by: Lukas Czerner <lczerner@xxxxxxxxxx> > > Suggested-by: Jan Kara <jack@xxxxxxx> > > --- > > v2: Reworked according to suggestions from Jan > > .... > > > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c > > index aa977c7ea370..cff05a4771b5 100644 > > --- a/fs/xfs/xfs_super.c > > +++ b/fs/xfs/xfs_super.c > > @@ -658,7 +658,8 @@ xfs_fs_dirty_inode( > > > > if (!(inode->i_sb->s_flags & SB_LAZYTIME)) > > return; > > - if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME)) > > + if ((flag & ~I_DIRTY_TIME) != I_DIRTY_SYNC || > > + !((inode->i_state | flag) & I_DIRTY_TIME)) > > return; > > My eyes, they bleed. The dirty time code was already a horrid > abomination, and this makes it worse. > > From looking at the code, I cannot work out what the new semantics > for I_DIRTY_TIME and I_DIRTY_SYNC are supposed to be, nor can I work Hi Dave, please see the other thready for this patch with Eric Biggers, where I try to explain and give some suggestion to change the doc. Does it make sense to you, or am I missing something? https://marc.info/?l=linux-ext4&m=165970194205621&w=2 > out what the condition this is new code is supposed to be doing. I > *can't verify it is correct* by reading the code. The ->dirty_inode() needed to be changed to clear I_DIRTY_TIME from i_state *before* we call ->dirty_inode() to avoid race where we would lose timestamp update that comes just a little later, after -dirty_inode() call with I_DRITY_INODE. But that would break xfs, so I decided to keep the condition and loosen the requirement so that I_DIRTY_TIME can also be se in 'flag', not just the i_state. Hence the abomination. > > Can you please add a comment here explaining the conditions where we > don't have to log a new timestamp update? How about something like this? Only do the timestamp update if the inode is dirty (I_DIRTY_SYNC) and has dirty timestamp (I_DIRTY_TIME). I_DIRTY_TIME can be either already set in i_state, or passed in flags possibly together with I_DIRTY_SYNC. > > Also, if "flag" now contains multiple flags, can you rename it > "flags"? Sure, I can do that. Thanks! -Lukas > > Cheers, > > Dave. > > -- > Dave Chinner > david@xxxxxxxxxxxxx >
