lazytime causing inodes to remain dirty after sync?
Subsystems (2)
While testing my patch "fscrypt: don't evict dirty inodes after removing key"
(https://lkml.kernel.org/r/[email protected]), I've run into an issue where even after the filesystem is sync'ed and no files are in-use, inodes can remain dirty if the filesystem is mounted with -o lazytime. Thus, my patch causes some inodes to not be evicted when they should be.
(lazytime is the default on f2fs, but ext4 supports it too.)
This is caused by the following code in __writeback_single_inode() that redirties the inode if its access time is dirty:
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);
if (ret == 0)
ret = err;
}
trace_writeback_single_inode(inode, wbc, nr_to_write);
return ret;Here's a reproducer in the kvm-xfstests test appliance which demonstrates the problem using sync(), without fscrypt involved at all:
sysctl vm.dirty_expire_centisecs=500
umount /vdc
mkfs.ext4 -F /dev/vdc
mount /vdc -o lazytime
echo contents > /vdc/file
sync
ino=$(stat -c %i /vdc/file)
echo 1 | tee /sys/kernel/debug/tracing/events/writeback/writeback_{single_inode_start,mark_inode_dirty,lazytime}/enable echo "ino == $ino" | tee /sys/kernel/debug/tracing/events/writeback/writeback_{single_inode_start,mark_inode_dirty,lazytime}/filter echo > /sys/kernel/debug/tracing/trace
cat /vdc/file > /dev/null
sync
cat /sys/kernel/debug/tracing/trace_pipe
The tracing shows that the inode for /vdc/file is written during the sync at 7.28s. But then, still during the sync, it's immediately re-dirtied. It then gets written again later in the background, after the sync.
cat-286 [001] ...1 7.279433: writeback_mark_inode_dirty: bdi 254:32: ino=12 state= flags=I_DIRTY_TIME
kworker/u8:0-8 [003] ...1 7.282647: writeback_single_inode_start: bdi 254:32: ino=12 state=I_SYNC|I_DIRTY_TIME|I_DIRTY_TIME_EXPIRED dirtied_when=4294879420 age=0 index=1 to_write=9223372036854775807 wrote=0 cgroup_ino=1
kworker/u8:0-8 [003] ...2 7.282660: writeback_lazytime: dev 254,32 ino 12 dirtied 4294879420 state I_SYNC|I_DIRTY_TIME|I_DIRTY_TIME_EXPIRED mode 0100644
kworker/u8:0-8 [003] ...1 7.283204: writeback_mark_inode_dirty: bdi 254:32: ino=12 state=I_SYNC flags=I_DIRTY_SYNC
kworker/u8:0-8 [003] ...1 12.412079: writeback_single_inode_start: bdi 254:32: ino=12 state=I_DIRTY_SYNC|I_SYNC dirtied_when=4294879421 age=5 index=1 to_write=13312 wrote=0 cgroup_ino=1Is this behavior intentional at all? It seems like a bug; it seems the inode should be written just once, during the sync.
- Eric
PATCH 1/1 writeback: avoid double-writing the inode on a lazytime expiration
In the case that an inode has dirty timestamp for longer than the lazytime expiration timeout (or if all such inodes are being flushed out due to a sync or syncfs system call), we need to inform the file system 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 file system supports lazytime, it will have ignored the dirty_inode(inode, I_DIRTY_TIME) notification when the timestamp was modified in memory.q
Previously, this was accomplished by calling mark_inode_dirty_sync(), but that has the unfortunate side effect of also putting the inode the writeback list, and that's not necessary in this case, since we will immediately call write_inode() afterwards.
Eric Biggers noticed that this was causing problems for fscrypt after the key was removed[1].
[1] https://lore.kernel.org/r/[email protected]
--- fs/fs-writeback.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
fs/fs-writeback.c +3 -2
@@ -1504,8 +1504,9 @@ __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); +/* This was a lazytime expiration; we need to tell the file system */ +if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_TIME_EXPIRED );/* Don't write the inode if only I_DIRTY_PAGES was set */ if (dirty & ~I_DIRTY_PAGES ) {int err =write_inode (inode, wbc);
Signature · 1 line
2.24.1
Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration
Quoted 31 lines · Theodore Ts'o
In the case that an inode has dirty timestamp for longer than the lazytime expiration timeout (or if all such inodes are being flushed out due to a sync or syncfs system call), we need to inform the file system 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 file system supports lazytime, it will have ignored the
dirty_inode(inode, I_DIRTY_TIME)notification when the timestamp was modified in memory.qPreviously, this was accomplished by calling
mark_inode_dirty_sync(), but that has the unfortunate side effect of also putting the inode the writeback list, and that's not necessary in this case, since we will immediately callwrite_inode()afterwards.Eric Biggers noticed that this was causing problems for fscrypt after the key was removed[1].
[1] https://lore.kernel.org/r/[email protected]
Reported-by Eric Biggers <[email protected]>Signed-off-by Theodore Ts'o <[email protected]>--- fs/fs-writeback.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)fs/fs-writeback.c +0
-0@@ -1504,8 +1504,9 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
fs/fs-writeback.c __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) · line 1512
Quoted 10 lines
fs/fs-writeback.c +3
-2spin_unlock (&inode->i_lock); -if (dirty &I_DIRTY_TIME ) -mark_inode_dirty_sync (inode); +/* This was a lazytime expiration; we need to tell the file system */ +if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_TIME_EXPIRED );/* Don't write the inode if only I_DIRTY_PAGES was set */ if (dirty & ~I_DIRTY_PAGES ) {int err =write_inode (inode, wbc);
Thanks Ted! This fixes the fscrypt test failure.
However, are you sure this works correctly on all filesystems? I'm not sure about XFS. XFS only implements ->dirty_inode(), not ->write_inode(), and in its ->dirty_inode() it does:
static void
xfs_fs_dirty_inode(
struct inode *inode,
int flag)
{
struct xfs_inode *ip = XFS_I(inode);
struct xfs_mount *mp = ip->i_mount;
struct xfs_trans *tp;
if (!(inode->i_sb->s_flags & SB_LAZYTIME))
return;
if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME))
return;
if (xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp))
return;
xfs_ilock(ip, XFS_ILOCK_EXCL);
xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
xfs_trans_log_inode(tp, ip, XFS_ILOG_TIMESTAMP);
xfs_trans_commit(tp);
}So flag=I_DIRTY_TIME_EXPIRED will be a no-op.
Maybe you should be using I_DIRTY_SYNC instead? Or perhaps XFS should be checking for either I_DIRTY_TIME_EXPIRED or I_DIRTY_SYNC?
- Eric
Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration
Quoted 5 lines · Eric Biggers
Thanks Ted! This fixes the fscrypt test failure.
However, are you sure this works correctly on all filesystems? I'm not sure about XFS. XFS only implements ->dirty_inode(), not ->write_inode(), and in its ->dirty_inode() it does:
...
Quoted 2 lines
if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME)) return;
That's true, but when the timestamps were originally modified, dirty_inode() will be called with flag == I_DIRTY_TIME, which will *not* be a no-op; which is to say, XFS will force the timestamps to be updated on disk when the timestamps are first dirtied, because it doesn't support I_DIRTY_TIME.
So I think we're fine.
- Ted
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Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration
Quoted 7 lines · Theodore Y. Ts'o
Quoted 5 lines · Eric Biggers
Thanks Ted! This fixes the fscrypt test failure.
However, are you sure this works correctly on all filesystems? I'm not sure about XFS. XFS only implements ->dirty_inode(), not ->write_inode(), and in its ->dirty_inode() it does:
...
Quoted 8 lines
Quoted 2 lines
if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME)) return;That's true, but when the timestamps were originally modified,
dirty_inode()will be called with flag ==I_DIRTY_TIME, which will *not* be a no-op; which is to say, XFS will force the timestamps to be updated on disk when the timestamps are first dirtied, because it doesn't supportI_DIRTY_TIME.
We log the initial timestamp change, and then ignore timestamp updates until the dirty time expires and the inode is set I_DIRTY_SYNC via __mark_inode_dirty_sync(). IOWs, on expiry, we have time stamps that may be 24 hours out of date in memory, and they still need to be flushed to the journal.
However, your change does not mark the inode dirtying on expiry anymore, so...
Quoted 1 line
So I think we're fine.
... we're not fine. This breaks XFS and any other filesystem that relies on a I_DIRTY_SYNC notification to handle dirty time expiry correctly.
Cheers,
Dave.
Signature · 2 lines
Dave Chinner [email protected]
Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration
Quoted 12 lines · Dave Chinner
Quoted 5 lines
That's true, but when the timestamps were originally modified,
dirty_inode()will be called with flag ==I_DIRTY_TIME, which will *not* be a no-op; which is to say, XFS will force the timestamps to be updated on disk when the timestamps are first dirtied, because it doesn't supportI_DIRTY_TIME.We log the initial timestamp change, and then ignore timestamp updates until the dirty time expires and the inode is set
I_DIRTY_SYNCvia__mark_inode_dirty_sync(). IOWs, on expiry, we have time stamps that may be 24 hours out of date in memory, and they still need to be flushed to the journal.
Quoted 8 lines
However, your change does not mark the inode dirtying on expiry anymore, so...
Quoted 1 line
So I think we're fine.
... we're not fine. This breaks XFS and any other filesystem that relies on a
I_DIRTY_SYNCnotification to handle dirty time expiry correctly.
I haven't seen the original mail this replies to, but if we could get the lazytime expirty by some other means (e.g. an explicit callback), XFS could opt out of all the VFS inode tracking again, which would simplify a few things.
Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration
Quoted 16 lines · Christoph Hellwig
Quoted 15 lines · Dave Chinner
Quoted 5 lines
That's true, but when the timestamps were originally modified,
dirty_inode()will be called with flag ==I_DIRTY_TIME, which will *not* be a no-op; which is to say, XFS will force the timestamps to be updated on disk when the timestamps are first dirtied, because it doesn't supportI_DIRTY_TIME.We log the initial timestamp change, and then ignore timestamp updates until the dirty time expires and the inode is set
I_DIRTY_SYNCvia__mark_inode_dirty_sync(). IOWs, on expiry, we have time stamps that may be 24 hours out of date in memory, and they still need to be flushed to the journal.However, your change does not mark the inode dirtying on expiry anymore, so...
Quoted 7 lines
Quoted 5 lines
Quoted 1 line
So I think we're fine.
... we're not fine. This breaks XFS and any other filesystem that relies on a
I_DIRTY_SYNCnotification to handle dirty time expiry correctly.I haven't seen the original mail this replies to,
The original problem was calling mark_inode_dirty_sync() on expiry during inode writeback was causing the inode to be put back on the dirty inode list and so ext4 was flushing it twice - once on expiry and once 5 seconds later on the next background writeback pass.
This is a problem that XFS does not have because it does not implement ->write_inode...
Quoted 4 lines
but if we could
get the lazytime expirty by some other means (e.g. an explicit callback), XFS could opt out of all the VFS inode tracking again, which would simplify a few things.
Yes, that would definitely make things simpler for XFS, and it would also solve the problem that the generic lazytime expiry code has....
Cheers,
Dave.
Signature · 2 lines
Dave Chinner [email protected]
Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration
In reply to Christoph HellwigQuoted 4 lines · Christoph Hellwig
I haven't seen the original mail this replies to, but if we could get the lazytime expirty by some other means (e.g. an explicit callback), XFS could opt out of all the VFS inode tracking again, which would simplify a few things.
Part of my thinking of calling
inode->i_sb->s_op->dirty_inode(inode, I_DIRTY_TIME_EXPIRED);
So that it would be an explicit callback to XFS. So why don't I break this as two patches --- one which uses I_DIRTY_SYNC, as before, and a second one which changes calls dirty_inode() with I_DIRTY_TIME_EXPIRED, and with a change to XFS so that it recognizes I_DIRTY_TIME_EXPIRED as if it were I_DIRTY_SYNC. If this would then allow XFS to simplify how it handles VFS tracking, you could do that in a separate patch.
Does that work? I'll send out the two patches, and if you can review/ack the second patch, that would be great.
- Ted
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PATCH 1/2 writeback: avoid double-writing the inode on a lazytime expiration
In the case that an inode has dirty timestamp for longer than the lazytime expiration timeout (or if all such inodes are being flushed out due to a sync or syncfs system call), we need to inform the file system 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 file system supports lazytime, it will have ignored the dirty_inode(inode, I_DIRTY_TIME) notification when the timestamp was modified in memory.q
Previously, this was accomplished by calling mark_inode_dirty_sync(), but that has the unfortunate side effect of also putting the inode the writeback list, and that's not necessary in this case, since we will immediately call write_inode() afterwards.
Eric Biggers noticed that this was causing problems for fscrypt after the key was removed[1].
[1] https://lore.kernel.org/r/[email protected]
--- fs/fs-writeback.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
fs/fs-writeback.c +3 -2
@@ -1504,8 +1504,9 @@ __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); +/* This was a lazytime expiration; we need to tell the file system */ +if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_SYNC );/* Don't write the inode if only I_DIRTY_PAGES was set */ if (dirty & ~I_DIRTY_PAGES ) {int err =write_inode (inode, wbc);
Signature · 8 lines
2.24.1 _______________________________________________ Linux-f2fs-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
PATCH 2/2 writeback, xfs: call dirty_inode() with I_DIRTY_TIME_EXPIRED when appropriate
Use the flag I_DIRTY_TIME_EXPIRED passed to dirty_inode() to signal to the file system that it is time to flush the inode's timestamps to stable storage.
--- fs/fs-writeback.c | 2 +- fs/xfs/xfs_super.c | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-)
fs/fs-writeback.c +1 -1
@@ -1506,7 +1506,7 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)/* This was a lazytime expiration; we need to tell the file system */ if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) - inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_SYNC ); + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_TIME_EXPIRED );/* Don't write the inode if only I_DIRTY_PAGES was set */ if (dirty & ~I_DIRTY_PAGES ) {int err =write_inode (inode, wbc);
fs/xfs/xfs_super.c +2 -1
@@ -622,7 +622,8 @@ 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_SYNC && flag !=I_DIRTY_TIME_EXPIRED ) || + !(inode->i_state &I_DIRTY_TIME ))return ;if (xfs_trans_alloc (mp, &M_RES (mp)->tr_fsyncts,0 ,0 ,0 , &tp))
Signature · 8 lines
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Re: [PATCH 2/2] writeback, xfs: call dirty_inode() with I_DIRTY_TIME_EXPIRED when appropriate
Christoph, Dave --- does this give you the notification that you were looking such that XFS could get the notification desired that it was the timestamps need to be written back?
- Ted
Quoted 40 lines · Theodore Ts'o
Use the flag
I_DIRTY_TIME_EXPIREDpassed todirty_inode()to signal to the file system that it is time to flush the inode's timestamps to stable storage.Signed-off-by Theodore Ts'o <[email protected]>--- fs/fs-writeback.c | 2 +- fs/xfs/xfs_super.c | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-)fs/fs-writeback.c +1
-1@@ -1506,7 +1506,7 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)/* This was a lazytime expiration; we need to tell the file system */ if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) - inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_SYNC ); + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_TIME_EXPIRED );/* Don't write the inode if only I_DIRTY_PAGES was set */ if (dirty & ~I_DIRTY_PAGES ) {int err =write_inode (inode, wbc);fs/xfs/xfs_super.c +2
-1@@ -622,7 +622,8 @@ 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_SYNC && flag !=I_DIRTY_TIME_EXPIRED ) || + !(inode->i_state &I_DIRTY_TIME ))return ;if (xfs_trans_alloc (mp, &M_RES (mp)->tr_fsyncts,0 ,0 ,0 , &tp))Signature · 1 line
2.24.1
Re: [PATCH 2/2] writeback, xfs: call dirty_inode() with I_DIRTY_TIME_EXPIRED when appropriate
Quoted 3 lines · Theodore Y. Ts'o
Christoph, Dave --- does this give you the notification that you were looking such that XFS could get the notification desired that it was the timestamps need to be written back?
I need to look at it in more detail as it seems convoluted. Also the order seems like you regress XFS in patch 1 and then fix it in patch 2?
Re: [PATCH 2/2] writeback, xfs: call dirty_inode() with I_DIRTY_TIME_EXPIRED when appropriate
Quoted 7 lines · Christoph Hellwig
Quoted 3 lines · Theodore Y. Ts'o
Christoph, Dave --- does this give you the notification that you were looking such that XFS could get the notification desired that it was the timestamps need to be written back?
I need to look at it in more detail as it seems convoluted. Also the order seems like you regress XFS in patch 1 and then fix it in patch 2?
In patch one we send I_DIRTY_SYNC as we had been doing as before. So I don't believe that patch #1 would regress XFS; can you confirm?
My thinking was to move ahead with patch 1 so that it fixed the bug which Eric Biffers had reported for f2fs, but only to move forward with patch #2 if it would be useful for XFS.
Cheers,
- Ted
Re: [PATCH 1/2] writeback: avoid double-writing the inode on a lazytime expiration
In reply to Theodore Ts'ofs/fs-writeback.c __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) · line 1509
Quoted 7 lines
fs/fs-writeback.c +3
-2spin_unlock (&inode->i_lock); -if (dirty &I_DIRTY_TIME ) -mark_inode_dirty_sync (inode); +/* This was a lazytime expiration; we need to tell the file system */ +if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_SYNC );
I think this needs a very clear comment explaining why we don't go through __mark_inode_dirty.
But as said before I'd rather have a new lazytime_expired operation that makes it very clear what is happening. We currenly have 4 file systems (ext4, f2fs, ubifs and xfs) that support lazytime, so this won't really be a major churn.
Re: [PATCH 1/2] writeback: avoid double-writing the inode on a lazytime expiration
Quoted 10 lines · Christoph Hellwig
fs/fs-writeback.c __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) · line 1509
Quoted 7 lines
fs/fs-writeback.c +3
-2spin_unlock (&inode->i_lock); -if (dirty &I_DIRTY_TIME ) -mark_inode_dirty_sync (inode); +/* This was a lazytime expiration; we need to tell the file system */ +if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_SYNC );I think this needs a very clear comment explaining why we don't go through
__mark_inode_dirty.
I can take the explanation which is in the git commit description and move it into the comment.
Quoted 4 lines
But as said before I'd rather have a new
lazytime_expiredoperation that makes it very clear what is happening. We currenly have 4 file systems (ext4, f2fs, ubifs and xfs) that support lazytime, so this won't really be a major churn.
Again, I believe patch #2 does what you want; if it doesn't can you explain why passing I_DIRTY_TIME_EXPIRED to s_op->dirty_inode() isn't "a new lazytime expired operation that makes very clear what is happening"?
I separated out patch #1 and patch #2 because patch #1 preserves current behavior, and patch #2 modifies XFS code, which I don't want to push Linus without an XFS reviewed-by.
N.b. None of the other file systems required a change for patch #2, so if you want, we can have the XFS tree carry patch #2, and/or combine that with whatever other simplifying changes that you want. Or I can combine patch #1 and patch #2, with an XFS Reviewed-by, and send it through the ext4 tree.
What's your pleasure?
- Ted
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Re: [PATCH 1/2] writeback: avoid double-writing the inode on a lazytime expiration
Quoted 29 lines · Theodore Y. Ts'o
Quoted 10 lines · Christoph Hellwig
fs/fs-writeback.c __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) · line 1509
Quoted 7 lines
fs/fs-writeback.c +3
-2spin_unlock (&inode->i_lock); -if (dirty &I_DIRTY_TIME ) -mark_inode_dirty_sync (inode); +/* This was a lazytime expiration; we need to tell the file system */ +if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_SYNC );I think this needs a very clear comment explaining why we don't go through
__mark_inode_dirty.I can take the explanation which is in the git commit description and move it into the comment.
Quoted 4 lines
But as said before I'd rather have a new
lazytime_expiredoperation that makes it very clear what is happening. We currenly have 4 file systems (ext4, f2fs, ubifs and xfs) that support lazytime, so this won't really be a major churn.Again, I believe patch #2 does what you want; if it doesn't can you explain why passing
I_DIRTY_TIME_EXPIREDtos_op->dirty_inode()isn't "a new lazytime expired operation that makes very clear what is happening"?I separated out patch #1 and patch #2 because patch #1 preserves current behavior, and patch #2 modifies XFS code, which I don't want to push Linus without an XFS reviewed-by.
Quoted 7 lines
N.b. None of the other file systems required a change for patch #2, so if you want, we can have the XFS tree carry patch #2, and/or combine that with whatever other simplifying changes that you want. Or I can combine patch #1 and patch #2, with an XFS Reviewed-by, and send it through the ext4 tree.
What's your pleasure?
TBH while I'm pretty sure this does actually maintain more or less the same behavior on xfs, I prefer Christoph's explicit ->lazytime_expired approach[1] over squinting at bitflag manipulations.
(It also took me a while to realize that this patch duo even existed, as it was kinda buried in its parent thread...)
--D
[1] https://lore.kernel.org/linux-fsdevel/[email protected]/T/#t
Quoted 3 lines
- Ted
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Re: [PATCH] writeback: avoid double-writing the inode on a lazytime expiration
In reply to Eric BiggersQuoted 72 lines · Eric Biggers
Quoted 31 lines · Theodore Ts'o
In the case that an inode has dirty timestamp for longer than the lazytime expiration timeout (or if all such inodes are being flushed out due to a sync or syncfs system call), we need to inform the file system 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 file system supports lazytime, it will have ignored the
dirty_inode(inode, I_DIRTY_TIME)notification when the timestamp was modified in memory.qPreviously, this was accomplished by calling
mark_inode_dirty_sync(), but that has the unfortunate side effect of also putting the inode the writeback list, and that's not necessary in this case, since we will immediately callwrite_inode()afterwards.Eric Biggers noticed that this was causing problems for fscrypt after the key was removed[1].
[1] https://lore.kernel.org/r/[email protected]
Reported-by Eric Biggers <[email protected]>Signed-off-by Theodore Ts'o <[email protected]>--- fs/fs-writeback.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)fs/fs-writeback.c +0
-0@@ -1504,8 +1504,9 @@ __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)fs/fs-writeback.c __writeback_single_inode(struct inode *inode, struct writeback_control *wbc) · line 1512
Quoted 10 lines
fs/fs-writeback.c +3
-2spin_unlock (&inode->i_lock); -if (dirty &I_DIRTY_TIME ) -mark_inode_dirty_sync (inode); +/* This was a lazytime expiration; we need to tell the file system */ +if (dirty &I_DIRTY_TIME_EXPIRED && inode->i_sb->s_op->dirty_inode) + inode->i_sb->s_op->dirty_inode (inode,I_DIRTY_TIME_EXPIRED );/* Don't write the inode if only I_DIRTY_PAGES was set */ if (dirty & ~I_DIRTY_PAGES ) {int err =write_inode (inode, wbc);Thanks Ted! This fixes the fscrypt test failure.
However, are you sure this works correctly on all filesystems? I'm not sure about XFS. XFS only implements ->dirty_inode(), not ->write_inode(), and in its ->dirty_inode() it does:
static void xfs_fs_dirty_inode( struct inode *inode, int flag) { struct xfs_inode *ip = XFS_I(inode); struct xfs_mount *mp = ip->i_mount; struct xfs_trans *tp; if (!(inode->i_sb->s_flags & SB_LAZYTIME)) return; if (flag != I_DIRTY_SYNC || !(inode->i_state & I_DIRTY_TIME)) return; if (xfs_trans_alloc(mp, &M_RES(mp)->tr_fsyncts, 0, 0, 0, &tp)) return; xfs_ilock(ip, XFS_ILOCK_EXCL); xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL); xfs_trans_log_inode(tp, ip, XFS_ILOG_TIMESTAMP); xfs_trans_commit(tp); }
Quoted 4 lines
So flag=I_DIRTY_TIME_EXPIRED will be a no-op.
Maybe you should be using
I_DIRTY_SYNCinstead? Or perhaps XFS should be checking for eitherI_DIRTY_TIME_EXPIREDorI_DIRTY_SYNC?
Right, XFS does not use the VFS inode writeback code at all - we track all metadata changes internally via journalling. The VFS uses I_DIRTY_SYNC to indicate and inode is metadata dirty and a writeback candidate. Hence if we need to mark an inode dirty for integrity purposes for _any reason_, then I_DIRTY_SYNC is the correct flag to be passing to ->dirty_inode.
Cheers,
Dave.
Signature · 2 lines
Dave Chinner [email protected]