6.10-stable review patch. If anyone has any objections, please let me know.
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From: David Howells dhowells@redhat.com
[ Upstream commit 212be98aa19303cbf376d61faf9de3ec9997c1cd ]
When netfslib is performing writeback (ie. ->writepages), it maintains two parallel streams of writes, one to the server and one to the cache, but it doesn't mark either stream of writes as active until it gets some data that needs to be written to that stream.
This is done because some folios will only be written to the cache (e.g. copying to the cache on read is done by marking the folios and letting writeback do the actual work) and sometimes we'll only be writing to the server (e.g. if there's no cache).
Now, since we don't actually dispatch uploads and cache writes in parallel, but rather flip between the streams, depending on which has the lowest so-far-issued offset, and don't wait for the subreqs to finish before flipping, we can end up in a situation where, say, we issue a write to the server and this completes before we start the write to the cache.
But because we only activate a stream when we first add a subreq to it, the result collection code may run before we manage to activate the stream - resulting in the folio being cleaned and having the writeback-in-progress mark removed. At this point, the folio no longer belongs to us.
This is only really a problem for folios that need to be written to both streams - and in that case, the upload to the server is started first, followed by the write to the cache - and the cache write may see a bad folio.
Fix this by activating the cache stream up front if there's a cache available. If there's a cache, then all data is going to be written to it.
Fixes: 288ace2f57c9 ("netfs: New writeback implementation") Signed-off-by: David Howells dhowells@redhat.com Link: https://lore.kernel.org/r/1599053.1721398818@warthog.procyon.org.uk cc: Jeff Layton jlayton@kernel.org cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- fs/netfs/write_issue.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/fs/netfs/write_issue.c b/fs/netfs/write_issue.c index d7c971df88660..32bc88bee5d18 100644 --- a/fs/netfs/write_issue.c +++ b/fs/netfs/write_issue.c @@ -122,6 +122,7 @@ struct netfs_io_request *netfs_create_write_req(struct address_space *mapping, wreq->io_streams[1].transferred = LONG_MAX; if (fscache_resources_valid(&wreq->cache_resources)) { wreq->io_streams[1].avail = true; + wreq->io_streams[1].active = true; wreq->io_streams[1].prepare_write = wreq->cache_resources.ops->prepare_write_subreq; wreq->io_streams[1].issue_write = wreq->cache_resources.ops->issue_write; }