From: Jan Kara <jack@suse.cz>
To: Eric Biggers <ebiggers@kernel.org>
Cc: linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net,
linux-xfs@vger.kernel.org, Theodore Ts'o <tytso@mit.edu>,
Christoph Hellwig <hch@lst.de>,
stable@vger.kernel.org
Subject: Re: [PATCH 01/13] fs: avoid double-writing inodes on lazytime expiration
Date: Thu, 7 Jan 2021 15:47:09 +0100 [thread overview]
Message-ID: <20210107144709.GG12990@quack2.suse.cz> (raw)
In-Reply-To: <20210105005452.92521-2-ebiggers@kernel.org>
[-- Attachment #1: Type: text/plain, Size: 4396 bytes --]
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);
> /* 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@suse.com>
SUSE Labs, CR
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[-- Type: text/x-patch, Size: 1913 bytes --]
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);
+ }
+
/*
* 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
next prev parent reply other threads:[~2021-01-07 14:47 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-05 0:54 [PATCH 00/13] lazytime fixes and cleanups Eric Biggers
2021-01-05 0:54 ` [PATCH 01/13] fs: avoid double-writing inodes on lazytime expiration Eric Biggers
2021-01-07 14:47 ` Jan Kara [this message]
2021-01-07 14:58 ` Matthew Wilcox
2021-01-07 21:46 ` Eric Biggers
2021-01-08 8:54 ` Christoph Hellwig
2021-01-08 9:01 ` Christoph Hellwig
2021-01-09 17:11 ` Eric Biggers
2021-01-05 0:54 ` [PATCH 02/13] gfs2: don't worry about I_DIRTY_TIME in gfs2_fsync() Eric Biggers
2021-01-08 8:54 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 03/13] fs: only specify I_DIRTY_TIME when needed in generic_update_time() Eric Biggers
2021-01-08 8:57 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 04/13] fat: only specify I_DIRTY_TIME when needed in fat_update_time() Eric Biggers
2021-01-07 13:13 ` Jan Kara
2021-01-07 19:10 ` Eric Biggers
2021-01-05 0:54 ` [PATCH 05/13] fs: don't call ->dirty_inode for lazytime timestamp updates Eric Biggers
2021-01-07 13:17 ` Jan Kara
2021-01-07 13:18 ` Jan Kara
2021-01-08 9:02 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 06/13] fs: pass only I_DIRTY_INODE flags to ->dirty_inode Eric Biggers
2021-01-08 9:02 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 07/13] fs: correctly document the inode dirty flags Eric Biggers
2021-01-08 9:03 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 08/13] ext4: simplify i_state checks in __ext4_update_other_inode_time() Eric Biggers
2021-01-07 13:24 ` Jan Kara
2021-01-07 19:06 ` Eric Biggers
2021-01-05 0:54 ` [PATCH 09/13] fs: drop redundant checks from __writeback_single_inode() Eric Biggers
2021-01-08 9:12 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 10/13] fs: clean up __mark_inode_dirty() a bit Eric Biggers
2021-01-08 9:10 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 11/13] fs: add a lazytime_expired method Eric Biggers
2021-01-07 14:02 ` Jan Kara
2021-01-07 22:05 ` Eric Biggers
2021-01-08 9:14 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 12/13] xfs: remove a stale comment from xfs_file_aio_write_checks() Eric Biggers
2021-01-08 9:15 ` Christoph Hellwig
2021-01-05 0:54 ` [PATCH 13/13] xfs: implement lazytime_expired Eric Biggers
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