Unverified Commit 38cf8e94 authored by David Howells's avatar David Howells Committed by Christian Brauner
Browse files

netfs: Fix ceph copy to cache on write-begin 



At the end of netfs_unlock_read_folio() in which folios are marked
appropriately for copying to the cache (either with by being marked dirty
and having their private data set or by having PG_private_2 set) and then
unlocked, the folio_queue struct has the entry pointing to the folio
cleared.  This presents a problem for netfs_pgpriv2_write_to_the_cache(),
which is used to write folios marked with PG_private_2 to the cache as it
expects to be able to trawl the folio_queue list thereafter to find the
relevant folios, leading to a hang.

Fix this by not clearing the folio_queue entry if we're going to do the
deprecated copy-to-cache.  The clearance will be done instead as the folios
are written to the cache.

This can be reproduced by starting cachefiles, mounting a ceph filesystem
with "-o fsc" and writing to it.

Fixes: 796a4049 ("netfs: In readahead, put the folio refs as soon extracted")
Reported-by: default avatarMax Kellermann <max.kellermann@ionos.com>
Closes: https://lore.kernel.org/r/CAKPOu+_4m80thNy5_fvROoxBm689YtA0dZ-=gcmkzwYSY4syqw@mail.gmail.com/


Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241213135013.2964079-10-dhowells@redhat.com


Fixes: ee4cdf7b ("netfs: Speed up buffered reading")
cc: Jeff Layton <jlayton@kernel.org>
cc: Ilya Dryomov <idryomov@gmail.com>
cc: Xiubo Li <xiubli@redhat.com>
cc: netfs@lists.linux.dev
cc: ceph-devel@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent 4acb665c

fs/netfs/read_collect.c

+4 −2
Original line number Diff line number Diff line
@@ -62,10 +62,14 @@ static void netfs_unlock_read_folio(struct netfs_io_subrequest *subreq, 
		} else {

			trace_netfs_folio(folio, netfs_folio_trace_read_done);

		}



		folioq_clear(folioq, slot);

	} else {

		// TODO: Use of PG_private_2 is deprecated.

		if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))

			netfs_pgpriv2_mark_copy_to_cache(subreq, rreq, folioq, slot);

		else

			folioq_clear(folioq, slot);

	}



	if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
@@ -77,8 +81,6 @@ static void netfs_unlock_read_folio(struct netfs_io_subrequest *subreq, 
			folio_unlock(folio);

		}

	}



	folioq_clear(folioq, slot);

}



/*