On Mon 04-01-21 16:54:40, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> 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@xxxxxxxxx
>
> 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@xxxxxxxxxxxxxxx
> Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
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);
> /* Don't write the inode if only I_DIRTY_PAGES was set */
> if (dirty & ~I_DIRTY_PAGES) {
> - 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);
> if (ret == 0)
> ret = err;
> }
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
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
>From 80ccc6a78d1c0532f600b98884f7a64e58333485 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@xxxxxxx>
Date: Thu, 7 Jan 2021 15:36:05 +0100
Subject: [PATCH] fs: Make sure inode is clean after __writeback_single_inode()
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/fs-writeback.c | 23 ++++++++++++-----------
1 file changed, 12 insertions(+), 11 deletions(-)
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index acfb55834af2..b9356f470fae 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1473,22 +1473,25 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
ret = err;
}
+ /*
+ * If inode has dirty timestamps and we need to write them, call
+ * mark_inode_dirty_sync() to notify filesystem about it.
+ */
+ if (inode->i_state & I_DIRTY_TIME &&
+ (wbc->for_sync || wbc->sync_mode == WB_SYNC_ALL ||
+ time_after(jiffies, inode->dirtied_time_when +
+ dirtytime_expire_interval * HZ))) {
+ trace_writeback_lazytime(inode);
+ mark_inode_dirty_sync(inode);
+ }
+
/*
* Some filesystems may redirty the inode during the writeback
* due to delalloc, clear dirty metadata flags right before
* write_inode()
*/
spin_lock(&inode->i_lock);
-
dirty = inode->i_state & I_DIRTY;
- if ((inode->i_state & I_DIRTY_TIME) &&
- ((dirty & I_DIRTY_INODE) ||
- wbc->sync_mode == WB_SYNC_ALL || wbc->for_sync ||
- time_after(jiffies, inode->dirtied_time_when +
- dirtytime_expire_interval * HZ))) {
- dirty |= I_DIRTY_TIME;
- trace_writeback_lazytime(inode);
- }
inode->i_state &= ~dirty;
/*
@@ -1509,8 +1512,6 @@ __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);
/* Don't write the inode if only I_DIRTY_PAGES was set */
if (dirty & ~I_DIRTY_PAGES) {
int err = write_inode(inode, wbc);
--
2.26.2
