At 02/20/2017 09:43 PM, Filipe Manana wrote:
On Mon, Feb 20, 2017 at 12:31 AM, Qu Wenruo <quwenruo@xxxxxxxxxxxxxx> wrote:
At 02/17/2017 11:25 PM, Filipe Manana wrote:
On Fri, Feb 17, 2017 at 12:37 AM, Qu Wenruo <quwenruo@xxxxxxxxxxxxxx>
wrote:
In case of an error the endio handler is called only for the first
page, and not for whole range for which one or more ordered extents
were created. So the ordered extents will be around forever.
That's the same thing I'm trying to fix.
While I'm asking the reason the cleanup previously created ordered extent,
which didn't encounter any error.
Any error in the loop requires cleaning up previously created ordered
extents, because if that function returns an error no bio is submitted
and therefore the ordered extents won't be removed, except for the
case where only one ordered extent is created and the delalloc range
is a single page.
Or is this a designed behavior for things like fsync?
Success for all or failure if any fails?
This is unrelated to fsync. It's about leaving ordered extents which
can make any task get them and hang on them forever.
However in the case of btrfs_reloc_clone_csum(), if it fails, there is only
one ordered extent really needs to clean.
The problem is more generic and you can forget about
btrfs_reloc_clone_csum(). It's about the delalloc callback returning
an error and one or more ordered extents were created by past
iterations of the loop before the error happened.
While the only possible problem we can hit after submitting an ordered
extent is btrfs_reloc_clone_csum().
Previously created ordered extent can finish without problem, so we only
need to clean the last created one, and no need to cleanup all ordered
extent that it created.
For a more specific example of this case:
We are relocating one data block group, whose size is 1G, containing 8 128M
file extents.
For run_delalloc_nocow(), it's called on root DATA_RELOC inode 257, range is
[0,1G),
And for first loop, it handles the first [0, 128M) without problem.
1st ordered extent is submitted and can finish even before submitting 2nd
ordered extent.
The ordered extent is submitted but not a bio for it. It's when the
bio completes (writeback finishes) that the endio callback is invoked,
which wakes up every task waiting on the ordered extent, sets IO
errors bit if needed, removes the ordered extent, etc.
Then when we are submitting 2nd ordered extent, ranged from [128M, 256M),
btrfs_reloc_clone_csum() fails. we must cleanup at least 2nd ordered extent
or it will hang forever.
If I understand your right, you mean we must cleanup all ordered extent in
the range [0, 1G).
Yes.
My point is, since 1st ordered extent can be submitted and finished before
2nd ordered extent submission without problem, I didn't see the point to
cleanup 1st ordered extent and non-exist 3rd~8th ordered extent.
As said before in this reply, if the delalloc callback
(cow_file_range, run_dellaloc_nocow) returns an error, no bios are
submitted for any ordered extents it might have created before an
error happened. Check __extent_writepage() - it calls
writepage_delalloc() which calls our delalloc callback, and if that
returns an error, it won't call __extent_writepage_io(), which is what
submits bios.
Or I missed or misunderstand something else?
You missed a lot of things I suppose, namely that bios aren't
submitted if the dealloc function returns an error.
That's the point. I misunderstand the bio submission timing, so in that
case you're right about cleanup the whole range.
I'll update the patch to address it.
Thanks,
Qu
Honestly I don't know how to explain things better to you, and was
hopping this was easier to understand using the direct IO write error
path as an example.
thanks
Thanks,
Qu
thanks
Thanks,
Qu
In that case, since we haven't unlock pages/extent, there will no race
nor
new ordered extent, and we are ensured to have only one ordered extent
need
cleanup.
Also, for any created ordered extent, you want to set the bit
BTRFS_ORDERED_IOERR on it before removing it, since there might be
concurrent tasks waiting for it that do error handling (like an fsync,
since when running delalloc the inode isn't locked).
Fsync is not affected IIRC, as btrfs_reloc_clone_csum() is only called
for
DATA_RELOC tree inode, which we don't call fsync on it.
Look at the direct IO write path error handling and
btrfs_endio_direct_write_update_ordered() for a very similar scenario.
And the same problem happens in the cow case
(inode.c:cow_file_range()).
BTW, I have already done it in cow_file_range(), check the beginning
lines
of inode.c of this patch.
Indeed. I missed it.
Thanks.
Thanks,
Qu
Thanks.
+ }
btrfs_free_path(path);
return ret;
}
diff --git a/fs/btrfs/ordered-data.c b/fs/btrfs/ordered-data.c
index 041c3326d109..dba1cf3464a7 100644
--- a/fs/btrfs/ordered-data.c
+++ b/fs/btrfs/ordered-data.c
@@ -650,6 +650,31 @@ void btrfs_remove_ordered_extent(struct inode
*inode,
wake_up(&entry->wait);
}
+void btrfs_clean_ordered_extent(struct inode *inode, u64
file_offset,
+ u64 ram_len)
+{
+ struct btrfs_ordered_extent *entry;
+ struct btrfs_root *root = BTRFS_I(inode)->root;
+
+ entry = btrfs_lookup_ordered_range(inode, file_offset,
ram_len);
+ if (!entry || entry->file_offset != file_offset ||
+ entry->len != ram_len)
+ goto not_found;
+
+ /* Same as btrfs_finish_ordered_io() */
+ btrfs_remove_ordered_extent(inode, entry);
+ btrfs_put_ordered_extent(entry);
+ btrfs_put_ordered_extent(entry);
+ return;
+
+not_found:
+ WARN_ON(1);
+ btrfs_err(root->fs_info,
+ "failed to find and clean ordered extent: root %llu ino %llu
file_offset %llu len %llu",
+ root->objectid, btrfs_ino(inode), file_offset,
ram_len);
+ return;
+}
+
static void btrfs_run_ordered_extent_work(struct btrfs_work *work)
{
struct btrfs_ordered_extent *ordered;
diff --git a/fs/btrfs/ordered-data.h b/fs/btrfs/ordered-data.h
index 5f2b0ca28705..7a989778aa89 100644
--- a/fs/btrfs/ordered-data.h
+++ b/fs/btrfs/ordered-data.h
@@ -163,6 +163,16 @@ btrfs_ordered_inode_tree_init(struct
btrfs_ordered_inode_tree *t)
void btrfs_put_ordered_extent(struct btrfs_ordered_extent *entry);
void btrfs_remove_ordered_extent(struct inode *inode,
struct btrfs_ordered_extent *entry);
+
+/*
+ * Function to cleanup an allocated ordered extent in error routine.
+ *
+ * As error handler in run_delalloc_range() will clear all related
pages
+ * and skip their IO, we have no method to finish inserted ordered
extent.
+ * So we must use this function to clean it up.
+ */
+void btrfs_clean_ordered_extent(struct inode *inode, u64
file_offset,
+ u64 ram_len);
int btrfs_dec_test_ordered_pending(struct inode *inode,
struct btrfs_ordered_extent
**cached,
u64 file_offset, u64 io_size, int
uptodate);
--
2.11.1
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