[PATCH AUTOSEL 6.1 10/20] Revert "gfs2: stop using generic_writepages in gfs2_ail1_start_one"

Sasha Levin
2023-01-31T15:00:41Z

From: Andreas Gruenbacher <agruenba@redhat.com>

[ Upstream commit 95ecbd0f162fc06ef4c4045a66f653f47b62a2d3 ]

Commit b2b0a5e97855 switched from generic_writepages() to
filemap_fdatawrite_wbc() in gfs2_ail1_start_one() on the path to
replacing ->writepage() with ->writepages() and eventually eliminating
the former. Function gfs2_ail1_start_one() is called from
gfs2_log_flush(), our main function for flushing the filesystem log.

Unfortunately, at least as implemented today, ->writepage() and
->writepages() are entirely different operations for journaled data
inodes: while the former creates and submits transactions covering the
data to be written, the latter flushes dirty buffers out to disk.

With gfs2_ail1_start_one() now calling ->writepages(), we end up
creating filesystem transactions while we are in the course of a log
flush, which immediately deadlocks on the sdp->sd_log_flush_lock
semaphore.

Work around that by going back to how things used to work before commit
b2b0a5e97855 for now; figuring out a superior solution will take time we
don't have available right now. However ...

Since the removal of generic_writepages() is imminent, open-code it
here. We're already inside a blk_start_plug() ... blk_finish_plug()
section here, so skip that part of the original generic_writepages().

This reverts commit b2b0a5e978552e348f85ad9c7568b630a5ede659.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/gfs2/log.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 723639376ae2..61323deb80bc 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -80,6 +80,15 @@ void gfs2_remove_from_ail(struct gfs2_bufdata *bd)
brelse(bd->bd_bh);
}

+static int __gfs2_writepage(struct page *page, struct writeback_control *wbc,
+ void *data)
+{
+ struct address_space *mapping = data;
+ int ret = mapping->a_ops->writepage(page, wbc);
+ mapping_set_error(mapping, ret);
+ return ret;
+}
+
/**
* gfs2_ail1_start_one - Start I/O on a transaction
* @sdp: The superblock
@@ -131,7 +140,7 @@ __acquires(&sdp->sd_ail_lock)
if (!mapping)
continue;
spin_unlock(&sdp->sd_ail_lock);
- ret = filemap_fdatawrite_wbc(mapping, wbc);
+ ret = write_cache_pages(mapping, wbc, __gfs2_writepage, mapping);
if (need_resched()) {
blk_finish_plug(plug);
cond_resched();
--
2.39.0