Re: [PATCH 01/13] fs: avoid double-writing inodes on lazytime expiration
From: Eric Biggers <ebiggers@kernel.org>
Date: 2021-01-07 21:47:32
Also in:
linux-ext4, linux-f2fs-devel, linux-fsdevel, stable
On Thu, Jan 07, 2021 at 03:47:09PM +0100, Jan Kara wrote:
quoted
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 [off-list ref] SUSE Labs, CR
quoted hunk ↗ jump to hunk
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);
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