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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:796a404964("netfs: In readahead, put the folio refs as soon extracted") Reported-by: Max Kellermann <max.kellermann@ionos.com> Closes: https://lore.kernel.org/r/CAKPOu+_4m80thNy5_fvROoxBm689YtA0dZ-=gcmkzwYSY4syqw@mail.gmail.com/ Signed-off-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/20241213135013.2964079-10-dhowells@redhat.com Fixes:ee4cdf7ba8("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: Christian Brauner <brauner@kernel.org>