Re: [uml-devel] btrfs failure and BUG_ON behaviour

[Sergei Trofimovich <slyich@gmail.com>]

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On Sat, 9 Apr 2011 23:33:14 +0200
richard -rw- weinberger <richard.weinberger@gmail.com> wrote:

> We have had some problems with the block layer in ~2.6.32 to 2.6.35.
> Commit 4752690 fixed the issues.
> 
> Can you please re-test it with 2.6.38?

Same crash with 2.6.38, so it's either very sneaky btrfs bug or
some discrepancy in ubd.

> Does you script work with other file systems?

Tested on ext4, xfs, jfs and reiserfs3. All survive
the load of creating and deleting 1000 files.

By on-disk load reiserfs3 should be quite similar to btrfs,
so I expected it to show problems, but it didn't.

[n00bish speculation] btrfs also plays games with mm. Maybe
the problem sits somewhere there where block layer/page
cache and on-disk layout gets out-of-sync.

[sf] ~/linux-2.6/fs/btrfs:fgrep -R PageDirty .
./extent_io.c:                          if (!PageDirty(pages[i]) ||
./extent_io.c:          if (!PageDirty(page))
./extent_io.c:          if (!PageDirty(page)) {
./disk-io.c:    if (PageDirty(page))
./disk-io.c:    if (PageWriteback(page) || PageDirty(page))
./disk-io.c:                    if (PageDirty(page)) {
./transaction.c:                                if (PageDirty(page))
./transaction.c:                        if (PageDirty(page)) {
./ioctl.c:              if (PageDirty(page)) {
./inode.c:      if (!page->mapping || !PageDirty(page) || !PageChecked(page)) {
./inode.c:      if (PageWriteback(page) || PageDirty(page))

I'll try to send bug report to linux-btrfs mailing list first
and return if I'll have more details.

-- 

  Sergei

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