在 2021/4/14 17:47, Miklos Szeredi 写道:
On Wed, Apr 14, 2021 at 11:22 AM Baolin Wang
<baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
在 2021/4/14 17:02, Miklos Szeredi 写道:
On Wed, Apr 14, 2021 at 10:42 AM Baolin Wang
<baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
Sorry I missed this patch before, and I've tested this patch, it seems
can solve the deadlock issue I met before.
Great, thanks for testing.
But look at this patch in detail, I think this patch only reduced the
deadlock window, but did not remove the possible deadlock scenario
completely like I explained in the commit log.
Since the fuse_fill_write_pages() can still lock the partitail page in
your patch, and will be wait for the partitail page waritehack is
completed if writeback is set in fuse_send_write_pages().
But at the same time, a writeback worker thread may be waiting for
trying to lock the partitail page to write a bunch of dirty pages by
fuse_writepages().
As you say, fuse_fill_write_pages() will lock a partial page. This
page cannot become dirty, only after being read completely, which
first requires the page lock. So dirtying this page can only happen
after the writeback of the fragment was completed.
What I mean is the writeback worker had looked up the dirty pages in
write_cache_pages() and stored them into a temporary pagevec, then try
to lock dirty page one by one and write them.
For example, suppose it looked up 2 dirty pages (named page 1 and page
2), and writed down page 1 by fuse_writepages_fill(), unlocked page 1.
Then try to lock page 2.
At the same time, suppose the fuse_fill_write_pages() will write the
same page 1 and partitail page 2, and it will lock partital page 2 and
wait for the page 1's writeback is completed. But page 1's writeback can
not be completed, since the writeback worker is waiting for locking page
2, which was already locked by fuse_fill_write_pages().
How would page2 become not uptodate, when it was already collected by
write_cache_pages()? I.e. page2 is a dirty page, hence it must be
uptodate, and fuse_writepages_fill() will not keep it locked.
Read your patch carefully again, now I realized you are right, and your
patch can solve the deadlock issue I met. Please feel free to add my
tested-by tag for your patch. Thanks.
Tested-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
