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 --- fs/fs-writeback.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)
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; }
base-commit: e71ba9452f0b5b2e8dc8aa5445198cd9214a6a62
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
On Thu, Jan 07, 2021 at 03:47:09PM +0100, Jan Kara wrote:
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?
I like this patch far more, fwiw.
On Thu, Jan 07, 2021 at 03:47:09PM +0100, Jan Kara wrote:
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-- Jan Kara jack@suse.com SUSE Labs, CR
From 80ccc6a78d1c0532f600b98884f7a64e58333485 Mon Sep 17 00:00:00 2001 From: Jan Kara jack@suse.cz 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@suse.cz
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);- }
- /*
*/ spin_lock(&inode->i_lock);
- Some filesystems may redirty the inode during the writeback
- due to delalloc, clear dirty metadata flags right before
- write_inode()
- 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);
It looks like that's going to work, and it fixes the XFS bug too.
Note that if __writeback_single_inode() is called from writeback_single_inode() (rather than writeback_sb_inodes()), then the inode might not be queued for sync, in which case mark_inode_dirty_sync() will move it to a writeback list.
That's okay because afterwards, writeback_single_inode() will delete the inode from any writeback list if it's been fully cleaned, right? So clean inodes won't get left on a writeback list.
It's confusing because there are comments in writeback_single_inode() and above __writeback_single_inode() that say that the inode must not be moved between writeback lists. I take it that those comments are outdated, as they predate I_SYNC_QUEUED being introduced by commit 5afced3bf281 ("writeback: Avoid skipping inode writeback")?
- Eric
On Thu, Jan 07, 2021 at 01:46:37PM -0800, Eric Biggers wrote:
It looks like that's going to work, and it fixes the XFS bug too.
Note that if __writeback_single_inode() is called from writeback_single_inode() (rather than writeback_sb_inodes()), then the inode might not be queued for sync, in which case mark_inode_dirty_sync() will move it to a writeback list.
That's okay because afterwards, writeback_single_inode() will delete the inode from any writeback list if it's been fully cleaned, right? So clean inodes won't get left on a writeback list.
It's confusing because there are comments in writeback_single_inode() and above __writeback_single_inode() that say that the inode must not be moved between writeback lists. I take it that those comments are outdated, as they predate I_SYNC_QUEUED being introduced by commit 5afced3bf281 ("writeback: Avoid skipping inode writeback")?
Yes. I think we need to update the comment as well.
- /*
* 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))) {
If we're touching this area, it would be nice to split this condition into a readable helper ala:
static inline bool inode_needs_timestamp_sync(struct writeback_control *wbc, struct inode *inode) { if (!(inode->i_state & I_DIRTY_TIME)) return false; if (wbc->for_sync || wbc->sync_mode == WB_SYNC_ALL) return true; return time_after(jiffies, inode->dirtied_time_when + dirtytime_expire_interval * HZ); }
On Fri, Jan 08, 2021 at 10:01:33AM +0100, Christoph Hellwig wrote:
- /*
* 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))) {If we're touching this area, it would be nice to split this condition into a readable helper ala:
static inline bool inode_needs_timestamp_sync(struct writeback_control *wbc, struct inode *inode) { if (!(inode->i_state & I_DIRTY_TIME)) return false; if (wbc->for_sync || wbc->sync_mode == WB_SYNC_ALL) return true; return time_after(jiffies, inode->dirtied_time_when + dirtytime_expire_interval * HZ); }
I didn't end up doing this since it would only be called once, and IMO it's more readable to keep it inlined next to the comment that explains what's going on. Especially considering the later patch that drops the check for wbc->for_sync.
- Eric
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